Pregnancy outcome in partners of male professional divers in Norway.

BACKGROUND: Diving is associated with both acute and long-term effects in several organ systems. Reduced semen quality after extreme diving and a reduced proportion of males in the offspring of divers have previously been reported. AIMS: To study pregnancy outcomes in partners of professional male divers. METHODS: The cohort of divers registered with the Norwegian Inshore Diving Registry was linked to the Medical Birth Registry of Norway (MBRN). RESULTS: In total, 6186 male divers had 10395 children registered in the MBRN during the study period. Of these, 52% were boys, compared to 51% in the general population. The partners of a subgroup of divers who were most likely to be occupationally exposed at the time of conception reported that early miscarriage was more frequent (27%) than in the general population (21%; relative risk 1.21, 95% confidence interval 1.05-1.39). Otherwise, there was a lower risk of adverse pregnancy outcomes such as preterm birth, stillbirth, low birthweight, small for gestational age and low Apgar score compared to the general population. Birthweight above 4000g was more frequent. CONCLUSIONS: We observed no reduced sex ratio in the offspring of occupational divers. Except for an increase in self-reported early miscarriage in the partners of exposed divers, we observed no excess risk of any of the adverse perinatal pregnancy outcomes studied.

Maternal obesity and excess of fetal growth in pre-eclampsia.

OBJECTIVE: To assess whether the reported excess of large for gestational age (LGA) neonates in pre-eclamptic women delivering at term is attributable to maternal obesity. DESIGN, SETTING AND POPULATION: Population-based observational study including 77,294 singleton pregnancies registered in the Medical Birth Registry of Norway between 2007 and 2010. METHODS: Comparison of birthweight percentiles and z-scores between women with and without pre-eclampsia. MAIN OUTCOME MEASURES: Odds ratio (OR) of LGA and z-scores of birthweight in relation to pre-eclampsia. RESULTS: Pre-eclamptic women delivering at term had increased risk of having LGA neonates. Unadjusted ORs with 95% confidence interval (95% CI) of LGA above the 90th and 95th birthweight centiles were 1.4, 95% CI 1.2-1.6 and 1.6, 95% CI 1.3-1.9, respectively. The excess of LGA persisted after including gestational diabetes and diabetes types 1 and 2 in a multivariate analysis (corresponding ORs 1.3, 95% CI 1.1-1.5 and 1.4, 95% CI 1.2-1.7), but disappeared after adjusting for maternal prepregnant body mass index (ORs 1.1, 95% CI 0.9-1.2 and 1.1, 95% CI 0.9-1.3). CONCLUSIONS: This study suggests accelerated fetal growth in a subset of pre-eclamptic women delivering at term. The excess of LGA neonates is attributable to maternal obesity among pre-eclamptic women delivering at term. The maternal obesity epidemic may lead to an increased prevalence of both pre-eclampsia and LGA neonates among women delivering at term.

Preterm birth time trends in Europe: a study of 19 countries.

OBJECTIVE: To investigate time trends in preterm birth in Europe by multiplicity, gestational age, and onset of delivery. DESIGN: Analysis of aggregate data from routine sources. SETTING: Nineteen European countries. POPULATION: Live births in 1996, 2000, 2004, and 2008. METHODS: Annual risk ratios of preterm birth in each country were estimated with year as a continuous variable for all births and by subgroup using log-binomial regression models. MAIN OUTCOME MEASURES: Overall preterm birth rate and rate by multiplicity, gestational age group, and spontaneous versus non-spontaneous (induced or prelabour caesarean section) onset of labour. RESULTS: Preterm birth rates rose in most countries, but the magnitude of these increases varied. Rises in the multiple birth rate as well as in the preterm birth rate for multiple births contributed to increases in the overall preterm birth rate. About half of countries experienced no change or decreases in the rates of singleton preterm birth. Where preterm birth rates rose, increases were no more prominent at 35-36 weeks of gestation than at 32-34 weeks of gestation. Variable trends were observed for spontaneous and non-spontaneous preterm births in the 13 countries with mode of onset data; increases were not solely attributed to non-spontaneous preterm births. CONCLUSIONS: There was a wide variation in preterm birth trends in European countries. Many countries maintained or reduced rates of singleton preterm birth over the past 15 years, challenging a widespread belief that rising rates are the norm. Understanding these cross-country differences could inform strategies for the prevention of preterm birth.

Familial risk of obstetric anal sphincter injuries: registry-based cohort study.

OBJECTIVE: To investigate the aggregation of obstetric anal sphincter injuries (OASIS) in relatives. DESIGN: Population-based cohort study. SETTING: The Medical Birth Registry of Norway from 1967 to 2008. POPULATION: All singleton, vertex-presenting infants weighing 500 g or more. Through linkage by national identification numbers, 393 856 mother-daughter pairs, 264 675 mother-son pairs, 134 889 mothers whose sisters later became mothers, 132 742 fathers whose brothers later became fathers, 131 702 mothers whose brothers later became fathers and 88 557 fathers whose sisters later became mothers were provided. METHODS: Comparison of women with and without a history of OASIS in their relatives. MAIN OUTCOME MEASURE: Relative risk of OASIS after a previous OASIS in the family. RESULTS: The risk of OASIS was increased if the woman's mother or sister had OASIS in a delivery (aRR 1.9, 95% CI 1.6-2.3; aRR 1.7, 95% CI 1.6-1.7, respectively). If OASIS occurred in one brother's partner at delivery, the risk of OASIS in the next brother's partner was modestly increased (aRR 1.2, 95% CI 1.1-1.4). If OASIS occurred in one sister at delivery, the risk of OASIS in the brother's partner was also increased a little (aRR 1.2, 95% CI 1.1-1.4). However, there was no excess occurrence in sisters whose brothers' partners had previously had OASIS (aRR 1.1, 95% CI 0.9-1.3). CONCLUSIONS: There appears to be increased familial aggregation of OASIS. These risks are stronger through the maternal rather than the paternal line of transmission, suggesting a strong genetic role that shapes aggregation of OASIS within families. These observations must be cautiously interpreted because of bias from unmeasured confounding factors may have impacted the findings.

Degree of fetal growth restriction associated with schizophrenia risk in a national cohort.

BACKGROUND: Accumulating evidence suggests that fetal growth restriction may increase risk of later schizophrenia but this issue has not been addressed directly in previous studies. We examined whether the degree of fetal growth restriction was linearly related to risk of schizophrenia, and also whether maternal pre-eclampsia, associated with both placental dysfunction and poor fetal growth, was related to risk of schizophrenia. METHOD: A population-based cohort of single live births in the Medical Birth Registry of Norway (MBRN) between 1967 and 1982 was followed to adulthood (n=873 612). The outcome was schizophrenia (n=2207) registered in the National Insurance Scheme (NIS). The degree of growth restriction was assessed by computing sex-specific z scores (standard deviation units) of ' birth weight for gestational age' and ' birth length for gestational age'. Analyses were adjusted for potential confounders. Maternal pre-eclampsia was recorded in the Medical Birth Registry by midwives or obstetricians using strictly defined criteria. RESULTS: The odds ratio (OR) for schizophrenia increased linearly with decreasing birth weight for gestational age z scores (p value for trend=0.005). Compared with the reference group (z scores 0.01­1.00), the adjusted OR [95% confidence interval (CI)] for the lowest z-score category (

Parity in patients with chronic inflammatory arthritides childless at time of diagnosis.

OBJECTIVE: To assess parity in women with chronic inflammatory arthritides (CIA) childless at time of diagnosis. METHODS: Patients were selected from the Norwegian Disease-Modifying Anti-Rheumatic Drug (NOR-DMARD) registry. Each patient was matched by year of birth with 100 reference women from the Norwegian Population Registry. Data linkage for patients and references with the Medical Birth Registry of Norway (MBRN) identified all offspring until time of linkage (October 2007). Patients and corresponding references childless at the time of diagnosis were included in the analyses. Kaplan-Meier curves visualized the proportion of childless women and were compared by a log rank test. RESULTS: In all, 156 rheumatoid arthritis (RA), 107 other chronic arthritides (OCA), and 75 juvenile idiopathic arthritis (JIA) patients were childless at time of diagnosis. At the time of data linkage, the proportions (%) of childless RA/OCA/JIA patients versus references were 61.5/62.6/57.3 versus 46.9/42.9/41.0, respectively, all differences statistically significant. The log rank test showed lower parity in all diagnostic groups compared with references (p < 0.001 for RA and OCA and p = 0.002 for JIA). No difference in parity was observed between RA and OCA patients, but both diagnostic groups had lower parity than JIA patients (p = 0.001). Disease characteristics were similar between childless and fertile patients. CONCLUSIONS: Reduced parity was observed in all diagnostic groups compared with references. RA and OCA patients had lower parity than JIA patients, indicating that having the disease as a young adult may influence parity more than having the disease in childhood.

Risk of recurrence and subsequent delivery after obstetric anal sphincter injuries.

OBJECTIVE: To investigate the recurrence risk, the likelihood of having further deliveries and mode of delivery after third to fourth degree obstetric anal sphincter injuries (OASIS). DESIGN: Population-based cohort study. SETTING: The Medical Birth Registry of Norway. POPULATION: A cohort of 828,864 mothers with singleton, vertex-presenting infants, weighing 500 g or more, during the period 1967-2004. METHODS: Comparison of women with and without a history of OASIS with respect to the occurrence of OASIS, subsequent delivery rate and planned caesarean rate. MAIN OUTCOME MEASURES: OASIS in second and third deliveries, subsequent delivery rate and mode of delivery. RESULTS: Adjusted odds ratios of the recurrence of OASIS in women with a history of OASIS in the first, and in both the first and second deliveries, were 4.2 (95% CI 3.9-4.5; 5.6%) and 10.6 (95% CI 6.2-18.1; 9.5%), respectively, relative to women without a history of OASIS. Instrumental deliveries, in particular forceps deliveries, birthweights of 3500 g or more and large maternity units were associated with a recurrence of OASIS. Instrumental delivery did not further increase the excess recurrence risk associated with high birthweight. A man who fathered a child whose delivery was complicated by OASIS was more likely to father another child whose delivery was complicated by OASIS in another woman who gave birth in the same maternity unit (adjusted OR 2.1; 95% CI 1.2-3.7; 5.6%). However, if the deliveries took place in different maternity units, the recurrence risk was not significantly increased (OR 1.3; 95% CI 0.8-2.1; 4.4%). The subsequent delivery rate was not different in women with and without previous OASIS, whereas women with a previous OASIS were more often scheduled to caesarean delivery. CONCLUSION: Recurrence risks in second and third deliveries were high. A history of OASIS had little or no impact on the rates of subsequent deliveries. Women with previous OASIS were delivered more frequently by planned caesarean delivery.

The origin of registry-based medical research and care.

During the last decades, registers comprising medical data have played an increasingly important role in medicine, both in health care and research. It is reasonable to expect that their importance will also increase in the future. Thus, a search for the origin of register-based medicine seems meaningful. Admittedly, collections of individual data on a number of patients may have occurred way back in history (Tidsskr Nor Laegeforen, 96, 1976:295). However, if we accept WHO's definition of a register, it implies more than a number of notifications. A register requires that a permanent record be established, that the cases be followed up and that basic statistical tabulations be prepared both on frequency and survival (Epidemiological Methods on the study of chronic diseases, Geneva, WHO Expert committee on Health Statistics, 1967). Thus, a register should aim at improving surveillance, health care and research. If we apply these criteria, we find the origin of register-based medicine in Norway in terms of the National Leprosy Registry, representing the world's first national patient register for any disease, established 1856 (Int J Epidemiol, 2, 1973: 81).

Postpartum onset of rheumatoid arthritis and other chronic arthritides: results from a patient register linked to a medical birth registry.

BACKGROUND: It is known that onset of rheumatoid arthritis (RA) is increased post partum. OBJECTIVE: To compare incidence rates between RA and other chronic arthritides (OCA) 0-24 months after delivery, and to compare the incidence rates within each group 0-24 versus 25-48 months post partum. METHODS: Premenopausal women from a Norwegian patient register were linked with the Medical Birth Registry of Norway to study the interval between delivery and time of diagnosis. Cox regression analysis with adjustments for age at delivery and birth order was applied to compare proportions of incident cases of RA and OCA with onset 0-24 months post partum. Poisson regression analysis with adjustment for the population at risk was applied to estimate the incidence rate ratio (IRR) 0-24 versus 25-48 months post partum. RESULTS: Of 183 RA and 110 patients with OCA diagnosed after delivery, 69 (37.7%) had RA and 31 (28.2%) OCA during the first 24 months post partum (p = 0.09). The IRR (95% CI) for diagnosis during 0-24 months versus 25-48 months was 1.73 (1.11 to 2.70) (p = 0.01) for RA, 1.05 (0.59 to 1.84) (p = 0.86) for OCA. The IRR was 2.23 (1.06 to 4.70) and 1.87 (0.67 to 5.21), respectively, when only considering diagnoses after the first pregnancy. Clinical characteristics were similar within each diagnostic group. CONCLUSION: The proportions of incident cases with onset 0-24 months after delivery were not different between RA and OCA. A peak in incidence during 0-24 months was seen in the RA group, both when considering all pregnancies and only the first pregnancy.

Mothers' negative affectivity during pregnancy and food choices for their infants.

OBJECTIVE: The objective of this study was to analyze whether maternal negative affectivity assessed in pregnancy is related with subsequent infant food choices. DESIGN: The study design was a cohort study. SUBJECTS: The subjects were mothers (N=37 919) and their infants participating in the Norwegian Mother and Child Cohort Study conducted by the Norwegian Institute of Public Health. MEASUREMENTS: Maternal negative affectivity assessed prepartum (Hopkins Symptom Checklist 5 (SCL-5) at weeks 17 and 30 of pregnancy), introduction of solid foods by month 3 and feeding of sweet drinks by month 6 (by the reports of the mothers) were analyzed. RESULTS: Mothers with higher negative affectivity were 64% more likely (95% confidence interval 1.5-1.8) to feed sweet drinks by month 6, and 79% more likely (95% confidence interval 1.6-2.0) to introduce solid foods by month 3. These odds decreased to 41 and 30%, respectively, after adjusting for mother's age, body mass index (BMI) and education. CONCLUSION: The maternal trait of negative affectivity is an independent predictor of infant feeding practices that may be related with childhood weight gain, overweight and obesity.

Neonatal mortality and morbidity in extremely preterm small for gestational age infants: a population based study.

AIM: To assess if growth restricted (small for gestational age, SGA) extremely preterm infants have excess neonatal mortality and morbidity. METHODS: This was a cohort study of all infants born alive at 22-27 weeks' post menstrual age in Norway during 1999-2000. Outcomes were compared between those who were SGA, defined as a birth weight less than the fifth percentile for post menstrual age, and those who had weights at or above the fifth percentile. RESULTS: Of 365 infants with a post menstrual age of <28 weeks, 31 (8%) were SGA. Among infants with a post menstrual age of <28 weeks, only chronic lung disease was associated with SGA status (OR 2.7, 95% CI 1.0 to 7.2). SGA infants with a post menstrual age of 26-27 weeks had excess neonatal mortality (OR 3.8, 95% CI 1.3 to 11), chronic lung disease and a significantly higher mean number of days (age) before tolerating full enteral nutrition. SGA infants with a post menstrual age of 22-25 weeks had an excess risk of necrotising enterocolitis. CONCLUSION: Extremely preterm SGA infants had excess neonatal mortality and morbidity in terms of necrotising enterocolitis and chronic lung disease.

Occurrence of placental abruption in relatives.

OBJECTIVE: The aim of this study was to assess the recurrence of placental abruption by severity, comparing the risk in a woman with that of recurrence in her sister and in the partner of her brother. DESIGN: Prospective observational study. SETTING: General population. POPULATION: Population-based study based on records of pregnancies from the Medical Birth Registry of Norway; 377.902 sisters with 767 395 pregnancies, 168,142 families incorporating 2-10 sisters, and 346,385 brothers with 717,604 pregnancies in their partners were identified. METHODS: Placental abruption with preterm birth, birthweight below 2500 g or perinatal death was defined as severe, other cases as mild. Because of the nested family data structure, multilevel multivariate regression was used. MAIN OUTCOME MEASURES: Placental abruption (severe and mild). RESULTS: Adjusted odds ratios of recurrence of mild and severe abruption were 6.5 (1.7%) and 11.5 (3.8%), respectively, compared with risks of 0.2 and 0.3% in the total population. After a severe abruption, odds ratios in her sisters were 1.7-2.1, whereas mild abruption produced no increased recurrence in sisters. The estimated heritability between sisters of severe abruption was 16%. No excess rate of abruption was observed between sisters and brothers' partners, between brothers' partners, or from brothers' partners to sisters. The odds ratios for a third abruption after a second abruption and a second severe abruption were 38.7 (19%) and 50.1 (24%), respectively. CONCLUSIONS: The recurrence risk of placental abruption in the same woman was higher after severe than mild abruption. Severe abruption was associated with a two-fold risk in sisters. Pregnancies following a second abruption should be considered very high risk.

Pregnancy and birth after kidney donation: the Norwegian experience.

Reports on pregnancies in kidney donors are scarce. The aim was to assess pregnancy outcomes for previous donors nationwide. The Medical Birth Registry of Norway holds records of births since 1967. Linkage with the Norwegian Renal Registry provided data on pregnancies of kidney donors 1967-2002. A random sample from the Medical Birth Registry was control group, as was pregnancies in kidney donors prior to donation. Differences between groups were assessed by two-sided Fisher's exact tests and with generalized linear mixed models (GLMM). We identified 326 donors with 726 pregnancies, 106 after donation. In unadjusted analysis (Fisher) no differences were observed in the occurrence of preeclampsia (p = 0.22). In the adjusted analysis (GLMM) it was more common in pregnancies after donation, 6/106 (5.7%), than in pregnancies before donation 16/620 (2.6%) (p = 0.026). The occurrence of stillbirths after donation was 3/106 (2.8%), before donation 7/620 (1.1%), in controls (1.1%) (p = 0.17). No differences were observed in the occurrence of adverse pregnancy outcome in kidney donors and in the general population in unadjusted analysis. Our finding of more frequent preeclampsia in pregnancies after kidney donation in the secondary analysis must be interpreted with caution, as the number of events was low.

Placenta weight percentile curves for singleton deliveries.

OBJECTIVE: To produce population-based, gender- and gestational-age-specific centile curves for placental weight. DESIGN: Population study. SETTING: Medical Birth Registry of Norway. POPULATION: All singleton live births in Norway from 1 January 1999 to 31 December 2002. METHODS: In a cohort of children born in Norway, placental weights and the ratio of the birthweight to the placental weight were analysed to produce percentile curves. MAIN OUTCOME MEASURES: Placental weight, birthweight-to-placental weight ratio. RESULTS: Tables and figures are presented for placental percentiles curves according to gestational age and gender. Also, tables and figures are presented for the ratio of birthweight to placental weight. CONCLUSIONS To our knowledge, this is the first time that population percentile curves have been produced for placental weights and hence for the ratio of birthweight to placental weight. These percentile curves may act as a reference for other populations as well until population-specific curves can be produced.

Reproduction and gynaecological manifestations in women with primary Sjögren's syndrome: a case-control study.

BACKGROUND: The impact of primary Sjögren's syndrome (pSS) on reproduction and gynaecological manifestations has seldom been explored. AIM OF STUDY: Assess gynaecological aspects, gynaecological interventions, and use of contraceptives in a population of pSS-patients versus controls. METHODS: In a case-control study, 58 pSS-patients and 157 controls answered a self-administered questionnaire, covering demographic data, reproductive events, gynaecological problems, and gynaecological interventions. RESULTS: Significantly more patients than controls reported episodes of amenorrhoea lasting for more than 3 months, and more patients suffered from menorrhagia/metrorrhagia compared with controls (54.5% versus 35.7%; p = 0.012). Complaints of vaginal dryness were common among the patients (52.9% versus 28.3%; p = 0.005). Endometriosis was reported to occur more frequently in the patients (8.5% versus 2.1%; p = 0.03), and 6.3% of pSS-patients reported having undergone surgical intervention for endometriosis versus 0.7% of the controls (p = 0.009). Positive information about surgery for endometriosis correlated with the presence of the autoantibodies anti-SSA (r = 0.322; p = 0.008) and anti-SSB (r = 0.313; p = 0.01). Among the pSS-patients, 5.9% had chosen not to have children due to the disease, but there was no indication of reduced fertility as judged by the number of pregnancies. CONCLUSION: Patients with pSS reported more gynaecological problems than controls, including vaginal sicca symptoms, endometriosis, several episodes of amenorrhoea, and menorrhagia/metrorrhagia.

Sudden unexplained infant death in 20 regions in Europe: case control study.

BACKGROUND: After striking changes in rates of sudden unexplained infant death (SIDS) around 1990, four large case-control studies were set up to re-examine the epidemiology of this syndrome. The European Concerted Action on SIDS (ECAS) investigation was planned to bring together data from these and new studies to give an overview of risk factors for the syndrome in Europe. METHODS: We undertook case-control studies in 20 regions. Data for more than 60 variables were extracted from anonymised records of 745 SIDS cases and 2411 live controls. Logistic regression was used to calculate odds ratios (ORs) for every factor in isolation, and to construct multivariate models. FINDINGS: Principal risk factors were largely independent. Multivariately significant ORs showed little evidence of intercentre heterogeneity apart from four outliers, which were eliminated. Highly significant risks were associated with prone sleeping (OR 13.1 [95% CI 8.51-20.2]) and with turning from the side to the prone position (45.4 [23.4-87.9]). About 48% of cases were attributable to sleeping in the side or prone position. If the mother smoked, significant risks were associated with bed-sharing, especially during the first weeks of life (at 2 weeks 27.0 [13.3-54.9]). This OR was partly attributable to mother's consumption of alcohol. Mother's alcohol consumption was significant only when baby bed-shared all night (OR increased by 1.66 [1.16-2.38] per drink). For mothers who did not smoke during pregnancy, OR for bed-sharing was very small (at 2 weeks 2.4 [1.2-4.6]) and only significant during the first 8 weeks of life. About 16% of cases were attributable to bed-sharing and roughly 36% to the baby sleeping in a separate room. INTERPRETATION: Avoidable risk factors such as those associated with inappropriate infants' sleeping position, type of bedding used, and sleeping arrangements strongly suggest a basis for further substantial reductions in SIDS incidence rates.

Circadian variations in sudden infant death syndrome: associations with maternal smoking, sleeping position and infections. The Nordic Epidemiological SIDS Study.

AIM: To study circadian variation in the sudden infant death syndrome (SIDS) and possible associations with risk factors for SIDS. METHODS: A questionnaire-based case-control study matched for place of birth, age and gender was conducted in Denmark, Norway and Sweden: The Nordic Epidemiological SIDS Study. The study comprised 244 SIDS victims and 869 control infants between September 1992 and August 1995. The main outcome was hour found dead. RESULTS: A significant circadian pattern was observed among the 242 SIDS victims with a known hour found dead, with a peak at 08.00-08.59 in the morning (n = 33). Of the SIDS victims, 12% were found dead at 00.00-05.59, 58% at 06.00-11.59, 21% at 12.00-17.59 and 9.0% at 18.00-23.59. When comparing night/morning SIDS and day/evening SIDS (found dead 00.00-11.59 and 12.00-23.59, respectively), the proportion of night/morning SIDS was high among infants of smoking mothers (81% vs 53%, p < 0.001), infants with a reported cold (82% vs 64%, p = 0.007) and infants sleeping side/supine (81% vs 60%, p < 0.001). No associations were observed between hour found dead and other sociodemographic risk factors for SIDS. Risk (odds ratio and 95% confidence interval) of night/morning SIDS and day/evening SIDS was 7.0 (4.5-10.9) and 1.5 (0.8-2.5), respectively, for maternal smoking, 2.2 (1.5-3.1) and 0.6 (0.3-1.3), respectively, if the infant had a reported cold, 3.7 (2.1-6.6) and 3.1 (1.1-8.4), respectively, if the infant was put to sleep in the side position (supine reference), and 11.0 (5.9-20.2) and 21.6 (7.6-60.8), respectively, if the infant was put to sleep in the prone position. CONCLUSION: The observed higher proportion of night/morning cases in SIDS if the mother smoked, if the infant was reported to have a cold and if the infant was sleeping side/supine may contribute to the understanding of some epidemiological characteristics of SIDS.

Vitamin A and sudden infant death syndrome in Scandinavia 1992-1995.

AIM: To assess the effect of vitamin supplementation on the risk of sudden infant death syndrome (SIDS). METHODS: The analyses are based on data from the Nordic Epidemiological SIDS Study, a case-control study in which parents of SIDS victims in the Scandinavian countries were invited to participate together with parents of four matched controls between 1 September 1992 and 31 August 1995. The odds ratios presented are computed by conditional logistic regression analysis. RESULTS: The crude odds ratio in Scandinavia for not giving vitamin substitution was 2.8 (95% CI (1.9, 4.3)). This effect was statistically significant in Norway and Sweden, which use A and D vitamin supplementation, but not in Denmark, where only vitamin D supplementation is given. The odds ratios remained significant in Sweden when an adjustment was made for confounding factors (OR 28.4, 95% CI (4.7, 171.3)). CONCLUSION: We found an association between increased risk of sudden infant death syndrome and infants not being given vitamin supplementation during their first year of life. This was highly significant in Sweden, and the effect is possibly connected with vitamin A deficiency. This effect persisted when an adjustment was made for potential confounders, includingsocioeconomic factors.

Comparative epidemiology of sudden infant death syndrome and sudden intrauterine unexplained death.

BACKGROUND: Unexplained antepartum stillbirth and sudden infant death syndrome (SIDS) are major contributors to perinatal and infant mortality in the western world. A relation between them has been suggested. As an equivalent of SIDS, only cases validated by post mortem examination are diagnosed as sudden intrauterine unexplained death (SIUD). OBJECTIVE: To test the hypothesis that SIDS and SIUD have common risk factors. METHODS: Registration comprised all stillbirths in Oslo and all infant deaths in Oslo and the neighbouring county, Akershus, Norway during 1986-1995. Seventy six cases of SIUD and 78 of SIDS were found, along with 582 random controls surviving infancy, all singletons. Odds ratios were obtained by multiple logistic regression analysis. RESULTS: Whereas SIUD was associated with high maternal age, overweight/obesity, smoking, and low education, SIDS was associated with low maternal age, smoking, male sex, multiparity, proteinuria during pregnancy, and fundal height exceeding +2 SD. Thus the effects of maternal age were opposite in SIUD and SIDS (adjusted odds ratio 1.39 (95% confidence interval 1.17 to 1.66) per year, p < 0.0005). Heavy smoking, male sex, and a multiparous mother was less likely in SIUD than in SIDS (0.22 (0.06 to 0.83), 0.22 (0.07 to 0.78), and 0.03 (<0.01 to 0.17) respectively). Overweight/obesity and low fundal height were more common in SIUD than in SIDS (7.45 (1.49 to 37.3) and 13.8 (1.56 to 122) respectively). CONCLUSIONS: The differences in risk factors do not support the hypothesis that SIDS and SIUD have similar determinants in maternal or fetal characteristics detectable by basic antenatal care.