Fertility treatment with clomiphene citrate and childhood epilepsy: a nationwide cohort study.

STUDY QUESTION: Is fertility treatment with clomiphene citrate associated with an increased risk of childhood epilepsy, including specific subtypes of epilepsy? SUMMARY ANSWER: Fertility treatment with clomiphene citrate may be associated with a small increased risk of idiopathic generalized epilepsy and focal epilepsy in childhood. WHAT IS KNOWN ALREADY: Clomiphene citrate is among the most commonly prescribed drugs for fertility treatment. However, concerns have been raised as to whether the treatment may harm the developing fetus. STUDY DESIGN, SIZE, DURATION: This nationwide cohort study included all pregnancies in Denmark from 1 July 1995 resulting in a live-born singleton child before 31 December 2013. The children were followed until 31 December 2016. PARTICIPANTS/MATERIALS, SETTING, METHODS: Children conceived after fertility treatment with clomiphene citrate were identified from the Danish National Prescription Registry. The primary outcomes were childhood epilepsy, idiopathic generalized epilepsy, and focal epilepsy identified from the Danish National Patient Register and from antiepileptic drug prescriptions in the Danish National Prescription Registry. All analyses were conducted using Cox proportional hazards regression. MAIN RESULTS AND THE ROLE OF CHANCE: A total of 1 081 291 pregnancies were included; 12 644 children (1.2%) developed epilepsy. Fertility treatment with clomiphene citrate was associated with a small increased risk of childhood epilepsy (hazard ratio [HR]: 1.10; 95% CI: 1.00-1.22), idiopathic generalized epilepsy (HR: 1.41; 95% CI: 1.16-1.72), and focal epilepsy (HR: 1.26; 95% CI: 1.04-1.53). LIMITATIONS, REASONS FOR CAUTION: The increased risk of idiopathic generalized epilepsy may be due to confounding from time stable parental characteristics related to treatment with clomiphene citrate, since the association was strongest with the lowest administered dosage of clomiphene citrate prior to conception, and the association disappeared in a sibling analysis. WIDER IMPLICATIONS OF THE FINDINGS: The increased risk of focal epilepsy may be related to the hormonal treatment, since the association tended to increase with increasing cumulative dosage of clomiphene citrate prior to conception, and the association persisted in a sibling analysis. This finding may be of clinical importance, since alternative hormones are available for fertility treatment. STUDY FUNDING/COMPETING INTEREST(S): Financial support from Aarhus University and the Aase and Ejnar Danielsen Foundation. U.S.K. received personal teaching fees from Merck, outside the submitted work. TRIAL REGISTRATION NUMBER: N/A.

Birth weight for gestational age and the risk of infertility: a Danish cohort study.

STUDY QUESTION: Is birth weight for gestational age associated with infertility in adulthood among men and women? SUMMARY ANSWER: Being born small for gestational age (SGA) was associated with infertility in adulthood among men. WHAT IS KNOWN ALREADY: Fetal growth restriction may affect fertility, but results from previous studies have been inconsistent. STUDY DESIGN, SIZE, DURATION: In this population-based cohort study, we used data from a Danish birth cohort, including 5594 men and 5342 women born between 1984 and 1987. Information on infertility was obtained from Danish health registers during the period from the participants' 18th birthday and up until 31 December 2017. PARTICIPANTS/MATERIALS, SETTING, METHODS: Participants were men and women born in two Danish municipalities, Aalborg and Odense. Information on birth weight and gestational age was obtained from birth records, and information on infertility diagnoses and fertility treatment was retrieved from the Danish National Patient Registry (NPR) and the Danish In Vitro Fertilisation (IVF) registry. Information on potential maternal confounders was obtained from questionnaires during pregnancy and was included in adjusted analyses. Logistic regression analysis was used to estimate crude and adjusted odds ratios (ORs) with 95% confidence intervals (CIs) for infertility according to birth weight for gestational age. MAIN RESULTS AND THE ROLE OF CHANCE: Men born SGA had a 55% higher risk of being diagnosed with or treated for infertility compared to men born appropriate for gestational age (AGA) (adjusted OR = 1.55, 95% CI: 1.09-2.21). The association attenuated after exclusion of men born with hypospadias or cryptorchidism (OR = 1.37, 95% CI: 0.93-2.01). No association was found between women's birth weight for gestational age and risk of infertility (adjusted OR = 1.00, 95% CI: 0.73-1.37). LIMITATIONS, REASONS FOR CAUTION: Estimation of gestational age is associated with some uncertainty and might have caused non-differential misclassification. The study design implicitly assumed similar distribution of reproductive and health-seeking behaviour across the groups that were compared. WIDER IMPLICATIONS OF THE FINDINGS: Men born SGA had a higher risk of infertility. Genital malformations may account for part of the observed association, but this must be explored further. STUDY FUNDING/COMPETING INTEREST(S): This study was supported by Health, Aarhus University. No competing interests are declared. TRIAL REGISTRATION NUMBER: N/A.

Oral contraceptive use and genital anomalies in sons. A Danish cohort study.

Exposure to exogenous sex hormones with estrogenic or anti-androgen properties may influence intrauterine development of male genitals. This population-based cohort study based on data from 44,408 live-born singleton sons in the Danish National Birth Cohort (DNBC) aimed to investigate whether maternal use of oral contraceptives prior to or during early pregnancy increase the risk of cryptorchidism or hypospadias. We found no consistent association between use of oral contraceptives and cryptorchidism or hypospadias, neither in those exposed any time four months prior to conception [cryptorchidism: adjusted Odds Ratio (aOR): 1.06 (95% CI: 0.91; 1.23), hypospadias: 0.74 (95% CI: 0.53; 1.03)] nor in those exposed any time during the first trimester of pregnancy [cryptorchidism: aOR: 0.93 (95% CI: 0.53; 1.62), hypospadias: 1.02 (95% CI: 0.32; 3.23)]. Despite relatively strong exposure levels from oral contraceptive use in pregnancy, this study revealed no evidence of an increased risk of either two genital malformations.

Low-to-moderate alcohol consumption and success in fertility treatment: a Danish cohort study.

STUDY QUESTION: Does female weekly alcohol intake and binge drinking impact the chance of a successful fertility treatment? SUMMARY ANSWER: Low-to-moderate weekly alcohol drinking and binge drinking were not associated with the chance of achieving a clinical pregnancy or a live birth among women and couples undergoing medically assisted reproduction (MAR) treatments. WHAT IS KNOWN ALREADY: Alcohol consumption is common among women of reproductive age, even though health authorities advise women trying to conceive to abstain from drinking. A growing number of couples struggle with infertility, but it is unknown whether low-to-moderate levels of alcohol consumption and alcohol binge drinking impair success in fertility treatment. STUDY DESIGN, SIZE, DURATION: Cohort study with prospectively collected exposure information including 1708 women and potential partners undergoing fertility treatment at the public fertility clinic, Aarhus University Hospital, 1 January 2010 to 31 August 2015. In total, data on 1511 intrauterine insemination (IUI) cycles, 2870 in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) cycles and 1355 frozen embryo transfer cycles. PARTTICIPANTS/MATERIALS, SETTING, METHODS: Exposure to weekly average alcohol intake was assessed from questionnaires completed by participants before the start of treatment. Outcome measures are the achievement of a clinical pregnancy and live birth in consecutive treatment cycles in the Danish national health registries, enabling complete follow-up. A modified Poisson regression with robust standard errors was used to evaluate associations between a weekly average alcohol intake and MAR outcomes, adjusting for female age, body mass index, cigarette smoking, coffee consumption, chronic diseases, level of education, and cycle number. When evaluating the association between binge drinking in the month prior to baseline and MAR outcomes the analyses were further adjusted for average weekly alcohol consumption. MAIN RESULTS AND THE ROLE OF CHANCE: Low-to-moderate average weekly alcohol intake was not statistically significantly associated with the chance of achieving a clinical pregnancy or a live birth following IUI or IVF/ICSI treatment cycles. Compared to women abstaining from alcohol, the adjusted relative risks for achieving a live birth among those reporting 1-2, 3-7, and >7 drinks per week were 1.00 (95% CI 0.66; 1.53), 1.20 (0.76; 1.91), and 1.48 (0.56; 3.93), respectively, among women initiating IUI treatments. Among those initiating IVF/ICSI treatments, the chance for achieving a live birth among those reporting 1-2, 3-7, and >7 drinks per week were 1.00 (0.83; 1.21), 0.95 (0.75; 1.20), and 0.89 (0.53; 1.51), respectively. The chance of achieving a live birth in the first IUI or IVF/ICSI treatment cycle was unrelated to the number of binge drinking episodes in the month preceding baseline. LIMITATIONS, REASONS FOR CAUTION: The risk of non-differential exposure misclassification, confounding, or chance cannot be ruled out. In addition, due to the low number of women reporting an intake of >7 drinks/week, the potential effect of high alcohol consumption should be interpreted with caution. WIDER IMPLICATIONS OF THE FINDINGS: Although it remains unsettled if and how alcohol affects female reproduction, our results indicate that is not necessary to abstain from alcohol when striving for a successful outcome following fertility treatment. STUDY FUNDING/COMPETING INTEREST(S): J.L. is supported by a fully financed Ph.D. scholarship from Aarhus University and has received funds from the A.P. Møller foundation. The funding sources had no involvement in the conduct of the article. Dr Kesmodel reports personal fees from MSD and Ferring Pharmaceuticals outside the submitted work. All other authors have no conflicts of interest to declare and all have completed the ICMJE disclosure form. TRIAL REGISTRATION NUMBER: Not relevant.

Parental time to pregnancy, medically assisted reproduction and pubertal development in boys and girls.

STUDY QUESTION: Does parental fertility, measured by time to pregnancy (TTP), or use of medically assisted reproduction (MAR) affect pubertal development in the offspring? SUMMARY ANSWER: Neither TTP nor type of MAR treatment had clinically relevant implications for mean age at achieving individual pubertal milestones or overall timing of puberty in boys and girls. WHAT IS KNOWN ALREADY: Parental TTP and MAR have been associated with impaired semen quality in adult sons. Timing of puberty reflects earlier signals of reproductive health, but it remains unclear whether parental fertility or MAR affects pubertal development, especially in the growing generation of children conceived by IVF or ICSI. STUDY DESIGN, SIZE, DURATION: In this study, 15 819 children born by mothers in the Danish National Birth Cohort from 2000 to 2003 participated in a nationwide puberty cohort (participation rate = 70%). Parental TTP and use of MAR were reported by mothers in early pregnancy and children's pubertal development data was self-recorded in web-based questionnaires from 11 years of age and 6 monthly throughout puberty (2012-2018). PARTICIPANTS/MATERIALS, SETTING, METHODS: Pubertal development in children (of planned pregnancies, n = 13 285) born by untreated subfecund (TTP: 6-12 months) (n =2038), untreated severely subfeund (TTP: >12 months) (n = 1242), treated subfecund (n = 230) and treated severely subfecund (n = 1234) parents were compared to children born to more fertile parents (TTP: ≤5 months). We estimated mean monthly differences in mean age at achieving individual pubertal milestones (i.e. age at menarche, voice break, first ejaculation and Tanner stages 2, 3, 4 and 5 for breast or genital development and pubic hair growth) and a combined indicator of timing of puberty. Further, we compared mean age at achieving the individual pubertal milestones in children born by use of IVF or ICSI (n = 480) with children born by controlled ovarian stimulation or ovulation induction with or without intrauterine insemination (n = 902). MAIN RESULTS AND THE ROLE OF CHANCE: We found tendencies towards slightly later mean age at male pubertal timing and slightly earlier mean age at female pubertal timing among children born by untreated subfecund, treated subfecund, untreated severely subfecund and treated severely subfecund parents. There were no specific patterns with increasing TTP, use of MAR nor type of MAR treatment, and the magnitude of the mean differences for individual milestones and overall timing of puberty were small, i.e. 0.9 months (95% CI: -1.0; 2.8) for first ejaculation and -0.5 months (95% CI: -2.0; 1.0) months for age at menarche in boys and girls, respectively, born by treated severely subfecund parents when compared with children born by more fertile parents. LIMITATIONS, REASONS FOR CAUTION: Non-differential misclassification of the self-reported information on parental TTP and pubertal development in the offspring may serve as an alternative explanation of the findings, possibly biasing the estimates towards the null. The information on pubertal development was collected from around 11 years of age and onwards. WIDER IMPLICATIONS OF THE FINDINGS: This study adds to the growing body of literature suggesting only limited harmful effects of parental subfecundity and MAR on offspring's long-term growth and development. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the Danish Council for Independent Research [DFF 4183-00152]; and the Faculty of Health at Aarhus University. The authors have no financial relationships or competing interests to disclose.

Maternal age at menarche and pubertal development in sons and daughters: a Nationwide Cohort Study.

STUDY QUESTION: Is maternal age at menarche associated with pubertal development in sons and daughters? SUMMARY ANSWER: Maternal age at menarche was associated with pubertal development in both sons and daughters. WHAT IS KNOWN ALREADY: Studies have shown that age at menarche is greatly inherited from mother to daughter, but it remains largely unknown to what extent age at menarche in mothers is associated with timing of puberty in sons. STUDY DESIGN, SIZE, DURATION: In this population-based study we used data from the Puberty Cohort nested within the Danish National Birth Cohort. Live-born singletons aged 11 were followed from 2012 to 2016. PARTICIPANTS/MATERIALS, SETTING, METHODS: In total, 15 822 children (7697 sons and 8125 daughters) gave half-yearly information on puberty from the age of 11 years until full sexual maturity or 18 years of age through self-administrated questionnaires (participation rate 71%). Information on maternal age at menarche was reported by the mothers during pregnancy. Maternal age at menarche was used both as a continuous and as a categorical variable (earlier, same time or later than peers). A multivariable regression model for interval-censored data was used. MAIN RESULTS AND THE ROLE OF CHANCE: Maternal age at menarche was positively associated with timing of genital development, pubic hair development, first ejaculation of semen, voice break, axillary hair development and acne in sons, and with timing of breast development, pubic hair development, menarche, axillary hair development and acne in daughters. In sons, the associations were of similar strength for all pubertal markers, whereas in daughters, the associations were strongest for breast development and menarche. LIMITATIONS, REASONS FOR CAUTION: Age at menarche was recalled during pregnancy. However, studies indicate that age at menarche is recalled moderately in adulthood. Information on puberty was self-reported, but inaccuracy of data would probably cause non-differential misclassification. WIDER IMPLICATIONS OF THE FINDINGS: Early maternal age at menarche was associated with earlier pubertal development, and late maternal age at menarche was associated with later pubertal development in both sons and daughters. The largest effect-estimates were for the associations between maternal age at menarche and the daughters' age at menarche and age at breast development. STUDY FUNDING/COMPETING INTEREST(S): The study was funded by the Danish Council for Independent Research (4183-00152). There are no competing interests. TRIAL REGISTERATION NUMBER: N/A.

Reproductive life in women with celiac disease; a nationwide, population-based matched cohort study.

STUDY QUESTION: How does celiac disease (CD) influence women's reproductive life, both prior to and after the diagnosis? SUMMARY ANSWER: Prior to the diagnosis of CD, an increased risk of adverse pregnancy outcomes was seen, whereas after the diagnosis, no influence on reproductive outcomes was found. WHAT IS KNOWN ALREADY: CD has been associated with several conditions influencing female reproduction and pregnancy outcomes including spontaneous abortion and stillbirth. STUDY DESIGN, SIZE, DURATION: A nationwide matched cohort study following 6319 women diagnosed with CD and 63166 comparison women and identifying reproductive events between the ages of 15 and 50 years. PARTICIPANTS/MATERIALS, SETTING, METHODS: Through linkage of several Danish national health registers, we identified all women diagnosed with CD between 1977 and 2016. We identified an age- and sex-matched comparison cohort and obtained data on reproductive outcomes for both cohorts. Adjusted stratified Cox and logistic regression models were used to estimate differences in reproductive outcomes between women with and without CD. MAIN RESULTS AND THE ROLE OF CHANCE: Comparing women with diagnosed CD with the non-CD women, the chance of pregnancy, live birth and risk of stillbirth, molar and ectopic pregnancy, spontaneous abortion and abortion due to foetal disease was the same. However, prior to being diagnosed, CD women had an excess risk of spontaneous abortion equal to 11 extra spontaneous abortions per 1000 pregnancies (adjusted odds ratio (OR) = 1.12, 95% CI: 1.03, 1.22) and 1.62 extra stillbirths per 1000 pregnancies (adjusted OR = 1.57, 95% CI: 1.05, 2.33) compared with the non-CD women. In the period 0-2 years prior to diagnosis fewer pregnancies occurred in the undiagnosed CD group, equal to 25 (95% CI: 20-31) fewer pregnancies per 1000 pregnancies compared to the non-CD group and in addition, fewer undiagnosed CD women initiated ART-treatment in this period, corresponding to 4.8 (95% CI: 0.9, 8.7) fewer per 1000 women compared to non-CD women. LIMITATIONS, REASONS FOR CAUTION: Validity of the diagnoses in the registers was not confirmed, but reporting to the registers is mandatory for all hospitals in Denmark. Not all spontaneous abortions will come to attention and be registered, whereas live- and stillbirths, ectopic and molar pregnancies and abortion due to foetal disease are unlikely not to be registered. We adjusted for several confounding factors but residual confounding cannot be ruled out. WIDER IMPLICATIONS OF THE FINDINGS: These findings suggest that undiagnosed CD can affect female reproduction and the focus should be on early detection of CD in risk groups. STUDY FUNDING/COMPETING INTEREST(S): This study was funded by the Health Research Fund of Central Denmark Region and The Hede Nielsens Foundation, Denmark. The authors report no conflicts of interest in this work.

Informal caregiving as a risk factor for type 2 diabetes in individuals with favourable and unfavourable psychosocial work environments: A longitudinal multi-cohort study.

AIM: To examine whether informal caregiving is associated with increased risk of type 2 diabetes (T2D), and whether job strain and social support at work modify the association. METHODS: Individual participant's data were pooled from three cohort studies-the French GAZEL study, the Swedish Longitudinal Occupational Survey of Health (SLOSH) and the British Whitehall II study-a total of 21,243 study subjects. Informal caregiving was defined as unpaid care for a closely related person. Job strain was assessed using the demand-control model, and questions on co-worker and supervisor support were combined in a measure of social support at work. Incident T2D was ascertained using registry-based, clinically assessed and self-reported data. RESULTS: A total of 1058 participants developed T2D during the up to 10 years of follow-up. Neither informal caregiving (OR: 1.09, 95% CI: 0.92-1.30) nor high job strain (OR: 1.04, 95% CI: 0.86-1.26) were associated with T2D risk, whereas low social support at work was a risk factor for T2D (OR: 1.18, 95% CI: 1.02-1.37). Also, informal caregivers who were also exposed to low social support at work were at higher risk of T2D (OR: 1.40, 95% CI: 1.08-1.82) compared with those who were not informal caregivers and had high social support at work (multiplicative test for interaction, P=0.04; additive test for interaction, synergy index=10). CONCLUSION: Informal caregiving was not independently associated with T2D risk. However, low social support at work was a risk factor, and informal caregivers with low social support at work had even higher risks of T2D.

Use of non-prescription analgesics and male reproductive function.

We studied the association between intake of non-prescription analgesics and semen quality and male reproductive hormone levels in a cross-sectional study among 1493 men. The men provided one semen (n=1493) and blood sample (n=1056) and filled in questionnaires on use of non-prescription analgesics (paracetamol, NSAIDs and combination drugs (yes/no)). Adjusting for age, study and other covariates, we observed no association between intake of non-prescription analgesics and markers of semen quality. Adjusting for age and time of day of blood sampling, users of non-prescription analgesics had a 10.4% (95% confidence interval (CI) 4.0-17.1%) higher testosterone level than non-users. When we stratified by medication type, the association between analgesics and higher testosterone was observed between users of non-steroidal anti-inflammatory drugs (NSAIDs) and combination drugs but not paracetamol. This study suggests that use of non-prescription analgesics is associated with slightly higher serum testosterone levels than non-use.

Prenatal antibiotics and atopic dermatitis among 18-month-old children in the Danish National Birth Cohort.

BACKGROUND: Despite extensive research, the aetiology of atopic dermatitis remains largely unknown, but reduced intestinal microbiota diversity in neonates has been linked to subsequent atopic dermatitis. Consequently, postnatal antibiotics have been proposed as a risk factor, but a potential association between prenatal antibiotics and atopic dermatitis is not well studied. Overall, the current evidence suggests a positive association between exposure to prenatal antibiotics and atopic dermatitis. OBJECTIVE: To investigate the association between prenatal antibiotics and atopic dermatitis among 18-month-old children. METHODS: This study conducted within the Danish National Birth Cohort included 62 560 mother-child pairs. Data on maternal prenatal antibiotics were collected in the 30th gestation week and 6 months post-partum, and offspring atopic dermatitis 18 months post-partum through telephone interviews. Antibiotic use was categorized by the timing of exposure as 1st-2nd trimester (gestation week 0-29), 3rd trimester (gestation week 30-birth), all three trimesters or none. Data were analysed by logistic regression analyses adjusting for potential confounders. RESULTS: Exposure to antibiotics prenatally was associated with increased odds of atopic dermatitis among children born by atopic mothers but only when used in both 1st-2nd and 3rd trimester (ORadj 1.45, 95% CI: 1.19-1.76). The findings were consistent using different definitions of atopic dermatitis. CONCLUSIONS AND CLINICAL RELEVANCE: Prenatal exposure to antibiotics throughout pregnancy was associated with an increased risk of atopic dermatitis but only within the first 18 months of life among children born by atopic mothers. The clinical usefulness of this finding must rest on corroboration in independent data sources.

Comparison of nurse practice environments in Denmark and the USA.

AIMS: The aims were to translate, validate and test the reliability of the Practice Environment Scale of the Nursing Work Index in a Danish context; and to compare Danish nurses' ratings of their nurse work environments with the highest rated work environments, USA magnet hospitals. BACKGROUND: Patient quality and safety are priorities for managers, administrators and policy makers worldwide. A supportive work environment is an important factor to improve quality and safety. The most used scale to measure the nurse work environment is Practice Environment Scale of the Nursing Work Index. There is no Danish translation of the scale or a comparison of nurse work environment between Denmark and other countries. METHODS: The translation and cultural adaption followed the steps recommended by the World Health Organization. Content validity was evaluated using cognitive interviewing in-person and through surveys. The reliability was tested using Cronbach's alpha. Finally, Practice Environment Scale of the Nursing Work Index ratings from 127 nurses were compared with results from Magnet and non-Magnet hospitals using t-tests. FINDINGS: The Danish translation of Practice Environment Scale of the Nursing Work Index had a high validity and reliability. Danish nurses rated their nurse work environment more favourable than nurses in non-Magnet hospitals and at the same level as Magnet hospitals. Lowest Danish scores were found in the two hospital-level subscales in items related to staff nurses' involvement in discussions on daily problems, the visibility of the chief nursing officer and importance of up-to-date nursing documentation. CONCLUSION: Danish nurses report a supportive nurse work environment with overall scores at the same level as Magnet hospitals. Opportunities for improvement were identified in the subscales. IMPLICATIONS FOR NURSING AND HEALTH POLICY: A first step to improve patient quality and safety is addressing factors that influence quality and safety. Using the Danish Practice Environment Scale of the Nursing Work Index, interventions to improve specific areas can be planned, implemented and evaluated. Further, Practice Environment Scale of the Nursing Work Index is a nursing quality indicator that can be included in quality databases in Denmark.

Age of menarche and time to pregnancy.

STUDY QUESTION: Is age of menarche (AOM) associated with subfecundity and/or infertility in adulthood? STUDY ANSWER: A late onset of menarche was associated with a slightly increased risk of subfecundity and infertility. WHAT IS KNOWN ALREADY: Abnormal age at onset of menarche is a risk factor for several diseases later in life, but the effect on infertility is unknown. STUDY DESIGN, SIZE AND DURATION: A cohort study of  73 107 pregnant Danish women enrolled in the Danish National Birth Cohort (DNBC) between 1996 and 2002 with self-reported data on AOM and waiting time to pregnancy (TTP). PARTICIPANTS/MATERIALS, SETTING AND METHODS: Information on AOM and TTP was collected through a computer-assisted telephone interview scheduled in pregnancy Week 12. We estimated adjusted odds ratios (ORs) with 95% confidence intervals (CIs) using multivariate logistic regression with TTP categorized as subfecundity (TTP ≥6 months) and infertility (TTP >12 months). Multiple imputation was performed to account for missing data. MAIN RESULTS AND THE ROLE OF CHANCE: We found trends towards higher odds of subfecundity and infertility with increasing age of menarche, using 13 years as the starting point. Among women reaching menarche at 15 years, the odds for subfecundity were 1.09 (95% CI: 1.03-1.15), and 1.17 (95% CI: 1.09-1.25) for women reaching menarche later than 15 years compared with the reference group of girls reaching menarche at 13 years. Additionally, women reaching menarche older than 15 years had an OR of infertility of 1.18 (95% CI: 1.08-1.29). Women younger than 11 years at menarche had lower odds of subfecundity. The results were generally attenuated when adjusting for women's age of pregnancy, but the significant positive trend of higher OR for subfecundity persisted, as did the higher OR for subfecundity among women experiencing menarche older than 15 years. LIMITATIONS, REASONS FOR CAUTION: We used retrospectively collected self-reported information on AOM and TTP. Information on male factors was limited in this cohort. We only included pregnant women and have therefore no data on women with untreated and unsuccessfully treated infertility, limiting the generalizability to women who became pregnant. WIDER IMPLICATION OF THE FINDINGS: This study indicates that the onset of menarche at 15 years or later is associated with subfecundity and infertility. STUDY FUNDING/COMPETING INTERESTS: The Danish National Research Foundation has established the Danish Epidemiology Science Centre that initiated and created the DNBC. The cohort is furthermore a result of a major grant from this Foundation. Additional support for the DNBC is obtained from the Pharmacy Foundation, the Egmont Foundation, the March of Dimes Birth Defects Foundation, the Augustinus Foundation and the Health Foundation. This specific study was supported by a scholarship from the Ministry of Science and Innovation. No conflict of interest declared.

Body mass index in young school-age children in relation to organochlorine compounds in early life: a prospective study.

OBJECTIVE: To investigate the association between maternal pregnancy and estimated postnatal serum concentrations of the organochlorines 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153) and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p,p'-DDE) and body mass index (BMI) z-scores in 5- to 9-year-old children. METHODS: Maternal sera from the INUENDO birth cohort (2002-2004) comprising mother-child pairs (N=1109) from Greenland, Warsaw (Poland), and Kharkiv (Ukraine) were analysed for CB-153 and p,p'-DDE, using gas chromatography-mass-spectrometry, and were grouped into tertiles for statistical analyses. A toxicokinetic model was used to estimate the first 12 months cumulative exposure to the compounds. Associations between these compounds and child age- and sex-specific BMI z-scores were calculated at follow-up (2010-2012), using multiple linear regression analysis. RESULTS: No clear associations between pregnancy CB-153 and p,p'-DDE and child BMI were observed (the pooled differences in BMI z-score (95% confidence interval) comparing 3rd tertile to 1st tertile were -0.07 (-0.32 to 0.18) and -0.10 (-0.30 to 0.10) kg m(-2), respectively). For postnatal CB-153 and p,p'-DDE and BMI, the overall differences in BMI z-score comparing 3rd tertile to 1st tertile were 0.12 (-0.15 to 0.39) and -0.03 (-0.20 to 0.27) kg m(-2), respectively. CONCLUSIONS: This follow-up study of Greenlandic, Polish and Ukrainian populations showed no clear association between pregnancy and postnatal exposure to p,p'-DDE and CB-153 and BMI at the age of 5-9 years.

Menstrual cycle characteristics in fertile women from Greenland, Poland and Ukraine exposed to perfluorinated chemicals: a cross-sectional study.

STUDY QUESTION: Does perfluorooctane sulfonate (PFOS) and perfluorooctanate (PFOA) exposure disrupt the menstrual cyclicity? SUMMARY ANSWER: The female reproductive system may be sensitive to PFOA exposure, with longer menstrual cycle length at higher exposure. WHAT IS KNOWN ALREADY: PFOS and PFOA are persistent man-made chemicals. Experimental animal studies suggest they are reproductive toxicants but epidemiological findings are inconsistent. STUDY DESIGN, SIZE, DURATION: A cross-sectional study including 1623 pregnant women from the INUENDO cohort enrolled during antenatal care visits between June 2002 and May 2004 in Greenland, Poland and Ukraine. PARTICIPANTS/MATERIALS, SETTING, METHODS: Information on menstrual cycle characteristics was obtained by questionnaires together with a blood sample from each pregnant woman. Serum concentrations of PFOS and PFOA were measured by liquid chromatography tandem mass spectrometry. Multiple imputations were performed to account for missing data. The association between PFOS/PFOA and menstrual cycle length (short cycle: ≤24 days, long cycle: ≥32 days) and irregularities (≥7 days in difference between cycles) was analyzed using logistic regression with tertiles of exposure. Estimates are given as adjusted odds ratios (ORs) with 95% confidence intervals (CIs). MAIN RESULTS AND THE ROLE OF CHANCE: Higher exposure levels of PFOA were associated with longer menstrual cycles in pooled estimates of all three countries. Compared with women in the lowest exposure tertile, the adjusted OR of long cycles was 1.8 (95% CI: 1.0; 3.3) among women in the highest tertile of PFOA exposure. No significant associations were observed between PFOS exposure and menstrual cycle characteristics. However, we observed a tendency toward more irregular cycles with higher exposure to PFOS [OR 1.7 (95% CI: 0.8; 3.5)]. The overall response rate was 45.3% with considerable variation between countries (91.3% in Greenland, 69.1% in Poland and 26.3% in Ukraine). LIMITATIONS, REASONS FOR CAUTION: Possible limitations in our study include varying participation rates across countries; a selected study group overrepresenting the most fertile part of the population; retrospective information on menstrual cycle characteristics; the determination of cut-points for all three outcome variables; and lacking information on some determinants of menstrual cycle characteristics, such as stress, physical activity, chronic diseases and gynecological disorders, thus confounding cannot be excluded. WIDER IMPLICATIONS OF THE FINDINGS: The generalizability of the study results is restricted to fertile women who manage to conceive and women who do not use oral contraceptives when getting pregnant or within 2 months before getting pregnant. To our knowledge only one previous epidemiological study has addressed the possible association between perfluorinated chemical exposure and menstrual disturbances. Though pointing toward different disturbances in cyclicity, both studies suggest that exposure to PFOA may affect the female reproductive function. This study contributes to the limited knowledge on effects of exposure to PFOA and PFOS on female reproductive function and suggests that the female reproductive system may be affected by environmental exposure to PFOA. STUDY FUNDING/COMPETING INTEREST(S): Supported by a scholarship from Aarhus University Research Foundation. The collection of questionnaire data and blood samples was part of the INUENDO project supported by The European Commission (Contract no. QLK4-CT-2001-00 202), www.inuendo.dk. The Ukrainian part of the study was possible by a grant from INTAS (project 012 2205). Determination of PFOA and PFOS in serum was part of the CLEAR study (www.inuendo.dk/clear) supported by the European Commission's 7th Framework Program (FP7-ENV-2008-1-226217). No conflict of interest declared.

Maternal pre-pregnancy body mass index and pubertal development among sons.

Maternal overweight and obesity in pregnancy has been associated with earlier age of menarche in daughters as well as reduced semen quality in sons. We aimed at investigating pubertal development in sons born by mothers with a high body mass index (BMI). The study included 2522 sons of mothers that during pregnancy in 1984-1987 were enrolled in a mother-child cohort and gave information on their pre-pregnancy height and weight from which we calculated their BMI. Information on sons' pubertal development, assessed by age when starting regular shaving, voice break, acne and first nocturnal emission, was obtained from web-based questionnaires in 2005, when sons were 18-21 years old. Multiple linear regression analyses showed that sons of obese mothers on average started to shave regularly 8.3 (95% confidence interval: 2.5-14.0) months earlier than sons of normal weight mothers. For the three other indicators of pubertal development, results also indicated earlier pubertal development among sons of obese mothers. After excluding sons of underweight mothers in a subanalysis, we observed an inverse trend between maternal pre-pregnancy BMI and age at regular shaving, acne and first nocturnal emission. In conclusion, maternal pre-pregnant obesity may be related to earlier timing of pubertal milestones among sons. More research, preferably based on prospectively collected information about pubertal development, is needed to draw firm conclusions.

Moderate alcohol intake and menstrual cycle characteristics.

STUDY QUESTION: Does moderate alcohol intake affect menstrual cycle characteristics among women in the Danish population? SUMMARY ANSWER: Levels of alcohol exposure as seen in this study do not substantially affect the menstrual cycle. WHAT IS KNOWN ALREADY: Animal studies indicate alcohol-induced disruptions of the reproductive system, but previous epidemiological studies addressing the possible association between alcohol intake and the menstrual cycle are sparse. STUDY DESIGN, SIZE, DURATION: A cross-sectional study with retrospectively collected data including 82 146 pregnant Danish women in the Danish National Birth Cohort (DNBC) enrolled during the years 1996-2002. PARTICIPANTS/MATERIALS, SETTING, METHODS: Information on weekly alcohol consumption and menstrual cycle characteristics before pregnancy was obtained through a computer-assisted telephone interview in pregnancy Week 12-16. The associations between weekly alcohol consumption and menstrual cycle irregularity (≥7 days difference between cycles) and length (short cycle: ≤24 days, long cycle: ≥32 days) were analysed using logistic regression with weekly alcohol intake categorized into abstainers (0 drinks per week), low (0.5-2.0 drinks per week), moderate (2.5-14.0 drinks per week) and high (14.0-86.5 drinks per week). Estimates are given as adjusted odds ratios with 95% confidence intervals. MAIN RESULTS AND THE ROLE OF CHANCE: The overall participation rate was 60% of the women invited. We found that a high weekly alcohol consumption was not associated with menstrual cycle disturbances. We observed higher odds of irregular and short cycles among abstainers when compared with women with a low weekly alcohol consumption, but found no trend of more cycle disturbances with higher alcohol consumption. LIMITATIONS, REASONS FOR CAUTION: Possible limitations in our study include a risk of selection bias due to the moderate participation rate and the use of retrospective information on alcohol exposure and menstrual cycle characteristics before getting pregnant. The higher odds of irregular and short cycles among abstainers may reflect other health problems in these women rather than an actual effect of alcohol on the menstrual cycle. WIDER IMPLICATIONS OF THE FINDINGS: The generalizability of the study results is restricted to women who manage to conceive and women who do not use oral contraceptives within 2 months before getting pregnant. This study suggests that the menstrual cycle is not substantially affected by higher alcohol consumption among the participating women. STUDY FUNDING/COMPETING INTEREST(S): Supported by a scholarship from Aarhus University Research Foundation. The Danish National Research Foundation has established the Danish Epidemiology Science Centre that initiated and created the DNBC. The cohort is furthermore a result of a major grant from this Foundation. Additional support for the DNBC is obtained from the Pharmacy Foundation, the Egmont Foundation, the March of Dimes Birth Defects Foundation, the Augustinus Foundation and the Health Foundation. No conflict of interest declared.

Long-term effects of prenatal exposure to perfluoroalkyl substances on female reproduction.

STUDY QUESTION: Does prenatal exposure to perfluoroalkyl substances (PFASs) have long-term effects on female reproductive function?. SUMMARY ANSWER: Our results suggest an association between in utero exposure to perfluorooctanoic acid (PFOA) and delay in age of menarche. WHAT IS KNOWN ALREADY: Previous cross-sectional studies have reported possible effects of PFASs on female reproduction including reduced fecundity, delayed puberty and accelerated age at menopause. Only limited data exist from follow-up studies on long-term implications of prenatal exposure to PFASs. STUDY DESIGN, SIZE, DURATION: In this study we used data from a Danish population-based cohort established in 1988-1989. Of 1212 eligible pregnant women, 965 participated. Follow-up was initiated in 2008 on the female offspring at ∼20 years of age. Three hundred and sixty seven (84%) daughters answered a questionnaire and 267 (61%) daughters furthermore attended clinical examinations which were conducted in 2008-2009. PARTICIPANTS/MATERIALS, SETTING, METHODS: The final study population consisted of 343 daughters of which 254 had attended the clinical examinations and 89 had answered the questionnaire only. Levels of PFASs in maternal serum from pregnancy week 30 were used as a measure of prenatal exposure and related to age of menarche, menstrual cycle length, levels of reproductive hormones and follicle number of the daughters. Data were divided into three groups according to tertiles of maternal concentrations of PFASs (low, medium, high). MAIN RESULTS AND THE ROLE OF CHANCE: In adjusted regression analyses, daughters exposed to higher levels of PFOA in utero had a 5.3 (95% confidence interval: 1.3; 9.3) months later age of menarche compared with the reference group of lower PFOA. Crude (P = 0.05) and adjusted (P = 0.01) trend tests also indicated a relationship between higher prenatal PFOA exposure and delay of menarche. LIMITATIONS, REASONS FOR CAUTION: We did not measure the exact amount of PFASs to which the daughters had been exposed prenatally. Instead we used PFAS concentrations in maternal serum as surrogates. However, PFASs are efficiently transferred to the fetus via placenta. Information on age of menarche was collected retrospectively but the time interval for recall in our study was relatively short (2-10 years). The remaining outcome measures depended on participation in clinical examination which reduced the number of observations leading to limited statistical power and risk of selection bias. WIDER IMPLICATIONS OF THE FINDINGS: Since PFASs can be detected in humans all over the world, effects of prenatal exposure on female reproductive function later in life may have wide health implications. STUDY FUNDING/COMPETING INTEREST(S): The study was supported by the Danish Council for Independent Research (271-05-0296, 09-065631), the Danish Ministry of Interior and Health (0-302-02-18/5), the Danish Council for Strategic Research (09-067124 (Centre for Fetal Programming), 09-063072, 2101-06-0005), the Novo Nordisk Foundation, the Aarhus University Research Foundation, the Frimodt-Heineke Foundation, the Foundation of Maria Dorthea and Holger From, the Beckett-Foundation, the Research Grant of Organon and the Foundation of Lily Benthine Lund. There are no competing interests. TRIAL REGISTRATION NUMBER: Not applicable.

Maternal cigarette smoking during pregnancy and pubertal development in sons. A follow-up study of a birth cohort.

Epidemiological studies have raised concern about the reproductive consequences of prenatal cigarette smoking exposure, possibly affecting semen quality and onset of pubertal development of the offspring. The aim of this study was to further investigate pubertal development in young men exposed to cigarette smoking in foetal life. In a Danish pregnancy cohort, information on maternal smoking during pregnancy was available from questionnaires administered in 1984-1987, and information on pubertal development, assessed by age at first nocturnal emission, acne, voice break and regular shaving, was obtained from a follow-up questionnaire administered in 2005 to the young men (age: 18-21). We found no significant association between prenatal cigarette smoking exposure and earlier onset of puberty, but we did observe a tendency towards earlier age of first nocturnal emission, acne and voice break, indicating an accelerated age of pubertal development. Men exposed to ≥15 cigarettes/day had 3.1 months (95% CI: -6.4; 0.2) earlier age at acne and 2.2 months (95% CI: -7.3; 3.0) earlier age at first nocturnal emission, 1.2 months (95% CI: -4.6; 2.2) earlier age at voice break, however, 1.3 months (95% CI: -1.6; 4.3) later age at regular shaving, compared with unexposed men. Prenatal cigarette smoking exposure may induce an earlier age at onset of puberty in young men, but larger studies with prospectively collected data on pubertal development are needed to explore this hypothesis further.