Progesterone concentrations on blastocyst transfer day in modified natural cycle frozen embryo transfer cycles.

RESEARCH QUESTION: Are serum progesterone concentrations on the day of modified natural cycle (mNC) frozen blastocyst transfer (FET) without luteal phase support (LPS) associated with clinical pregnancy rate (CPR)? DESIGN: Data were collected between January 2019 and October 2022 as a sub-study of an ongoing randomized controlled trial assessing pregnancy outcomes in mNC-FET. The sub-study included all women (n = 209) randomized to mNC-FET without LPS at the time of data extraction. Participants were aged 18-41 years, had regular menstrual cycles and underwent mNC-FET treatment with single-blastocyst transfer. Associations between the serum progesterone concentration on the day of blastocyst transfer and CPR, pregnancy rate and pregnancy loss rate (PLR) were examined between groups with low and higher progesterone concentrations using the 25th and 10th percentiles as cut-offs. Multivariate logistic regression analyses were performed to adjust for potential confounding factors. RESULTS: Progesterone concentrations on the day of blastocyst transfer in mNC-FET without LPS ranged from 4.9 to 91.8 nmol/l, with the 25th and 10th percentiles at 29.0 nmol/l and 22.5 nmol/l, respectively. Serum progesterone concentrations did not differ between women with or without a clinical pregnancy (mean [SD] 38.5 [14.0] versus 36.8 [12.4] nmol/l; P = 0.350). Furthermore, the CPR, pregancy rate and PLR were similar in women with low or high progesterone concentrations when using the 25th or the 10th progesterone percentile as cut-off. Multivariate regression analyses showed no association between progesterone concentrations and CPR. CONCLUSIONS: No association was found between progesterone concentration on the day of blastocyst transfer and pregnancy outcome in women undergoing mNC-FET without progesterone LPS.

The prevalence of late-follicular phase progesterone elevation and impact on the ongoing pregnancy rate after fresh and frozen blastocyst transfer. Sub-study of an RCT.

The effect of late-follicular phase progesterone elevation (LFPE) during ovarian stimulation on reproductive outcomes in ART treatment remains controversial, but recent studies indicate lower pregnancy rates with rising progesterone levels. This study aims to investigate the prevalence of late-follicular phase progesterone elevation (LFPE) and possible impact on ongoing pregnancy rate after fresh or frozen blastocyst transfer in a sub-study setting of a randomised controlled trial. A total of 288 women were included (n=137 and n=151 in the fresh transfer and freeze-all group, respectively). Among these 11(3.8%) had a progesterone level ≥1.5 ng/ml, and 20(6.9%) had a progesterone level ≥1.2 ng/ml on trigger day. Spline regression analysis showed no significant effect of late follicular phase progesterone levels on ongoing pregnancy. In the multivariate regression analysis (n = 312) only age, but not progesterone level on trigger day was significantly associated with ongoing pregnancy. In conclusion, in a clinical setting with moderate gonadotrophin stimulation and well-defined trigger and fresh transfer cancellation criteria, the prevalence of women with LFPE ≥1.5 ng/ml was low and did not indicate the clinical value of routine measurement of progesterone in the late follicular phase.

Psychosocial wellbeing shortly after allocation to a freeze-all strategy compared with a fresh transfer strategy in women and men: a sub-study of a randomized controlled trial.

STUDY QUESTION: Is the psychosocial wellbeing affected in women and men shortly after allocation to a freeze-all strategy with postponement of embryo transfer compared to a fresh transfer strategy? SUMMARY ANSWER: In general, psychosocial wellbeing (i.e. emotional reactions to the treatment, quality-of-life, infertility-related stress, and marital benefit) was similar in women and men allocated to a freeze-all versus those allocated to a fresh-transfer strategy 6 days after disclosure of treatment strategy (i.e. 4 days after oocyte retrieval), although women in the freeze-all group reported a slightly higher degree of depressive symptoms and mood swings compared to women in the fresh transfer group. WHAT IS KNOWN ALREADY: The use of a freeze-all strategy, i.e. freezing of the entire embryo cohort followed by elective frozen embryo transfer in subsequent cycles has increased steadily over the past decade in assisted reproductive technology (ART). This strategy essentially eliminates the risk of ovarian hyperstimulation syndrome and has proven beneficial regarding some reproductive outcomes in subgroups of women. However, patients experience a longer time interval between oocyte retrieval and embryo transfer, hence a longer time to pregnancy, possibly adding additional stress to the ART treatment. So far, little focus has been on the possible psychosocial strains caused by postponement of embryo transfer. STUDY DESIGN, SIZE, DURATION: This is a self-reported questionnaire based sub-study of a multicentre randomized controlled trial (RCT) including 460 women and 396 male partners initiating their first, second, or third treatment cycle of invitro fertilisation or intracytoplasmic sperm injection (ICSI) from May 2016 to September 2018. This sub-study was included in the primary project protocol and project plan for the RCT, as psychosocial wellbeing was considered a secondary outcome. PARTICIPANTS/MATERIALS, SETTING, METHODS: Women from eight public fertility clinics in Denmark and Sweden and one private clinic in Spain were randomized in a 1:1 ratio on the day of inclusion (menstrual cycle day 2 or 3) to either a freeze-all strategy with postponement of embryo transfer to a subsequent modified natural menstrual cycle or a fresh transfer strategy with embryo transfer in the hormone stimulated cycle. Treatment allocation was blinded until the day of the ovulation trigger. Women and their male partners were asked to complete a validated self-reported questionnaire 6 days after unblinding of treatment group allocation, corresponding to 4 days after oocyte retrieval, investigating their psychosocial wellbeing related to the treatment defined as emotional reactions to the treatment, quality-of-life, infertility-related stress, and marital benefit. The questionnaire included items from the Copenhagen Multi-Centre Psychosocial Infertility (COMPI) Fertility Problem Stress Scales and the COMPI Marital Benefit Measure. MAIN RESULTS AND THE ROLE OF CHANCE: Baseline characteristics were comparable between the two groups for both women and men. In total, response rates were 90.7% for women and 90.2% for men. In the freeze-all group, 207 women and 179 men completed the questionnaire compared with 204 women and 178 men in the fresh transfer group. Men in the two treatment groups did not differ in any of the explored aspects of psychosocial wellbeing (i.e. emotional reactions to the treatment, quality-of-life, infertility-related stress, and marital benefit) 6 days after disclosure of treatment strategy. Women in the freeze-all group reported a slightly higher degree of depressive symptoms (P = 0.045) and mood swings (P = 0.001) (i.e. variables included in 'emotional reactions to treatment') compared to women in the fresh transfer group. When adjusted for multiple testing, depressive symptoms were no longer significantly different between the two groups. No additional differences in psychosocial wellbeing were found. Self-reported quality-of-life during treatment was also rated as similar between the two groups in both women and men, but was slightly lower than they would rate their quality-of-life when not in fertility treatment. LIMITATIONS, REASONS FOR CAUTION: Although response rates were high, selection bias cannot be excluded. As this study was an RCT, we assume that psychosocial characteristics of the participants were equally distributed in the two groups, thus it is unlikely that the identified psychosocial differences between the freeze-all and fresh transfer group were present already at baseline. Furthermore, the questionnaire was completed as a one-time assessment 4 days after oocyte retrieval, thus not reflecting the whole treatment process, whereas an assessment after the full completed treatment cycle is needed to draw firm conclusions about the psychosocial consequences of the whole waiting period. However, a question posted that late would be highly biased on whether or not a pregnancy had been achieved. WIDER IMPLICATIONS OF THE FINDINGS: The results indicate that individuals in the freeze-all group exhibited slightly higher levels of depressive symptoms and mood swings compared to those in the fresh transfer group. Nevertheless, it is important to note that any worries related to potential emotional strains stemming from delaying embryo transfer should not overshadow the adoption of a freeze-all approach in cases where it is clinically recommended. As long as patients are provided with comprehensive information about the treatment strategy before initiating the process, it is worth emphasising that other aspects of psychosocial wellbeing were comparable between the two groups. STUDY FUNDING/COMPETING INTEREST(S): The study is part of the Reprounion collaborative study, co-financed by the European Union, Interreg V Öresund-Kattegat-Skagerrak. L.P. reports financial support from Merck A/S. H.S.N. reports grants from Freya Biosciences ApS, Ferring Pharmaceuticals, BioInnovation Institute, Ministry of Education, Novo Nordic Foundation, Augustinus Fonden, Oda og Hans Svenningsens Fond, Demant Fonden, Ole Kirks Fond and Independent Research Fund Denmark and personal fees from Ferring Pharmaceuticals, Merck A/S, Astra Zeneca, Cook Medical, IBSA Nordic and Gedeon Richter. H.S.N is founder and chairman of the Maternity Foundation and co-developed the Safe Delivery App (non-profit). N.C.F. reports grants from Gedeon Richter, Merck A/S, Cryos International and financial support from Ferring Pharmaceuticals, Merck A/S and Gedeon Richter. N.C.F. is chairman in the steering committee for the guideline groups for The Danish Fertility Society (non-profit). P.H. reports honoraria from Merch A/S, IBSA Nordic and Gedeon Richter. A.L.M.E. reports grants and financial support from Merck A/S and Gedeon Richter. A.P. reports grants from Gedeon Richter, Ferring Pharmaceuticals, Merck A/S and personal fees from Preglem S.A., Novo Nordic Foundation, Ferring Pharmaceuticals, Gedeon Richter, Cryos International, Merch A/S, Theramex and Organon and the lend of embryoscope to the institution from Gedeon Richter. All other authors declare no conflict of interest. TRIAL REGISTRATION NUMBER: Clinicaltrials.gov NCT02746562.

Does luteal phase progesterone supplementation affect physical and psychosocial well-being among women undergoing modified natural cycle-FET? A sub-study of a randomized controlled trial.

STUDY QUESTION: Are there any differences in physical and psychosocial well-being among women undergoing modified natural cycle frozen embryo transfer (mNC-FET) with or without vaginal progesterone as luteal phase support (LPS)? SUMMARY ANSWER: Women undergoing mNC-FET with vaginal progesterone supplementation were more likely to experience physical discomfort but there was no difference in psychosocial well-being between the two groups. WHAT IS KNOWN ALREADY: mNC-FET can be carried out with or without vaginal progesterone as LPS, which has several side-effects. It is commonly known that fertility treatment can cause stress and psychosocial strain, however, most studies on this subject are conducted in fresh cycle regimes, which differ from NC-FET and results may not be comparable. STUDY DESIGN, SIZE, DURATION: This is a sub-study of an ongoing RCT investigating whether progesterone supplementation has a positive effect on live birth rate in mNC-FET. The RCT is conducted at eight fertility clinics in Denmark from 2019 and is planned to end primo 2024. The sub-study is based on two questionnaires on physical and psychosocial well-being added to the RCT in August 2019. On the time of data extraction 286 women had answered both questionnaires. PARTICIPANTS/MATERIALS, SETTING, METHODS: Women who had answered both questionnaires were included in the sub-study. Participants were equally distributed, with 143 in each of the two groups. Participants in both groups received the same questionnaires at two time-points: on cycle day 2-5 (baseline) and after blastocyst transfer. Participants in the progesterone group had administered progesterone for 7 days upon answering the second questionnaire. All items in the questionnaires were validated. Items on psychosocial well-being originate from the Copenhagen Multi-Centre Psychosocial Infertility-Fertility Problem Stress Scale (COMPI-FPSS) and from the Mental Health Inventory-5. MAIN RESULTS AND THE ROLE OF CHANCE: Women receiving progesterone experienced more vaginal itching and/or burning than women in the non-progesterone group (P < 0.001). Women in the progesterone group also experienced more self-reported vaginal yeast infection, this was, however, not significant after adjustment for multiple testing (P/adjusted P = 0.049/0.881). No differences regarding psychosocial well-being were found between the two groups. Within the progesterone group, a shift toward feeling less 'downhearted and blue' was found when comparing response distribution at baseline and after blastocyst transfer (P < 0.001). LIMITATIONS, REASONS FOR CAUTION: All items on physical symptoms were self-reported. The item on vaginal yeast infection was therefore not diagnosed by a doctor. Inclusion in the study required a few extra visits to the clinic, participants who felt more burdened by fertility treatment might have been more likely to decline participation. Women who experienced a lot of side-effects to progesterone prior to this FET cycle, might be less likely to participate. WIDER IMPLICATIONS OF THE FINDINGS: Our results are in line with previous known side-effects to progesterone. Physical side-effects of progesterone should be considered before administration. STUDY FUNDING/COMPETING INTEREST(S): The RCT is fully supported by Rigshospitalet's Research Foundation and a grant from Gedeon Richter. Gedeon Richter were not involved in the design of protocol nor in the conduction of the study or analysis of results. A.P., L.P., and N.I.-C.F. report grants from Gedeon Richter, Ferring and Merck with no relations to this study. N.I.-C.F. has received travel support from Ferring, Merck A/S, & Gideon Richter, and is the head of the steering committee for the Danish Fertility Guidelines made by the members of from the Danish Fertility Society. A.P. reports consulting fees from Preglem, Novo Nordisk, Ferring, Gedeon Richter, Cryos, & Merck A/S, honoraria from Gedeon Richter, Ferring, Merck A/S, Theramex, and Organon, has received travel support from Gedeon Richter (payment to institution), participated on an advisory board for Preglem and was loaned an embryoscope from Gedeon Richter to their institution. A.L.S. has stock options for Novo Nordisk B A/S. B.A. have received unrestricted grant from Gedeon Richter Nordic and Merck and honoraria for lectures from Gedeon Richter, Merck, IBSA, and Marckyrl Pharma. TRIAL REGISTRATION NUMBER: The RCT is registered on ClinicalTrials. gov (NCT03795220) and in EudraCT (2018-002207-34).

Low-grade inflammation is negatively associated with live birth in women undergoing IVF.

RESEARCH QUESTION: Is low-grade inflammation, detected by C-reactive protein (CRP), a marker of IVF outcome addressing both blastocyst quality and pregnancy outcome? DESIGN: This sub-study of a multicentre randomized controlled trial included 440 women undergoing IVF treatment with a gonadotrophin-releasing hormone (GnRH) antagonist protocol. Serum CRP was measured on cycle day 2-3 (baseline) and on the day of ovulation triggering. The association between CRP concentrations and reproductive outcomes (number of retrieved oocytes, number of good-quality blastocysts, pregnancy, pregnancy loss and live birth), were analysed, adjusting for relevant confounders. RESULTS: A negative association was found between higher baseline CRP concentrations and live birth rate (odds ratio [OR] 0.77, 95% confidence interval [CI] 0.62-0.96, P = 0.02) and higher CRP concentrations at baseline were associated with pregnancy loss among women who conceived (OR 1.37, 95% CI 1.07-1.76, P = 0.01). When testing for a specific cut-off, CRP concentrations above 2.34 (the highest quartile) were more likely to be associated with pregnancy loss (P = 0.02) and a lower chance of live birth (P = 0.04) compared with the lowest quartile. No associations were found between CRP concentrations and pregnancy outcomes on the day of ovulation triggering, and there were no associations between CRP concentrations and the number of good-quality blastocysts. CONCLUSIONS: Higher CRP concentrations at cycle day 2-3, before starting ovarian stimulation, are negatively associated with chance of live birth, possibly because of an increased risk of pregnancy loss. No association was found between the number of good-quality blastocysts and CRP concentration. More studies are needed to investigate the impact of low-grade inflammation.

Microdissection Testicular Sperm Extraction Versus Multiple Needle-pass Percutaneous Testicular Sperm Aspiration in Men with Nonobstructive Azoospermia: A Randomized Clinical Trial.

BACKGROUND: Surgical extraction of testicular spermatozoa is needed in men with nonobstructive azoospermia (NOA) who wish to become biological fathers. Based on available uncontrolled studies with unspecific patient selection, microdissection testicular sperm extraction (mTESE), having a sperm retrieval rate (SRR) of 50%, is considered the most efficient sperm retrieval procedure. However, no randomized clinical trials for comparison of different sperm retrieval procedures exist. Testicular sperm aspiration (TESA) is simple and commonly used, and we hypothesized that this technique using multiple needle passes would give similar SRRs to mTESE. OBJECTIVE: To compare mTESE and multiple needle-pass TESA in men with NOA. DESIGN, SETTING, AND PARTICIPANTS: A randomized clinical trial was performed between June 2017 and April 2021, with inclusion of 100 men with NOA from four centers in Denmark and Sweden. All participants received treatment at the same institution. INTERVENTION: Participants were randomized to mTESE (n = 49) or multiple needle-pass TESA (n = 51). Patients with failed multiple needle-pass TESA proceeded directly to salvage mTESE. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: The primary outcome was SRR. Secondary outcomes included complications and changes in reproductive hormones after surgery. RESULTS AND LIMITATIONS: Spermatozoa were retrieved in 21/49 (43%) men after mTESE and in 11/51 (22%) men after multiple needle-pass TESA (rate difference -0.21; 95% confidence interval -0.39 to -0.03; p = 0.02). The combined SRR for multiple needle-pass TESA + salvage mTESE was 15/51 (29%). No complications occurred after multiple needle-pass TESA only, while 5/89 (6%) men having mTESE experienced a complication requiring surgical intervention. Overall, no statistically significant differences in reproductive hormones were observed between groups after 6 mo. Limitations include the low number of patients in secondary outcome data. CONCLUSIONS: In direct comparison, SRR was higher in mTESE than in multiple needle-pass TESA. PATIENT SUMMARY: Men with azoospermia need surgical extraction of spermatozoa to become biological fathers. In this randomized trial, we compared two surgeries (microdissection testicular sperm extraction [mTESE] and testicular sperm aspiration [TESA]) and found that mTESE gives a higher sperm retrieval rate than multiple needle-pass TESA.

[Intrauterine insemination with or without ovarian stimulation is often a first-choice treatment for infertility].

In Denmark, intrauterine insemination (IUI) with or without ovarian stimulation is a common treatment for infertility. If strict cancellation criteria are met to reduce the risk of multiple pregnancies in ovarian stimulation cycles, IUI can be considered safe, less invasive and less costly compared to in vitro fertilisation. In 2019, a total of 9,322 homologous IUIs and 8,433 IUIs using donor sperm were performed in Denmark, and 2,000 children were expected to be born after the use of IUI. Thus, in this review we conclude that IUI is an effective treatment for infertility in selected patients.

Weight reduction intervention for obese infertile women prior to IVF: a randomized controlled trial.

STUDY QUESTION: Does an intensive weight reduction programme prior to IVF increase live birth rates for infertile obese women? SUMMARY ANSWER: An intensive weight reduction programme resulted in a large weight loss but did not substantially affect live birth rates in obese women scheduled for IVF. WHAT IS ALREADY KNOWN: Among obese women, fertility and obstetric outcomes are influenced negatively with increased risk of miscarriage and a higher risk of maternal and neonatal complications. A recent large randomized controlled trial found no effect of lifestyle intervention on live birth in infertile obese women. STUDY DESIGN, SIZE, DURATION: A prospective, multicentre, randomized controlled trial was performed between 2010 and 2016 in the Nordic countries. In total, 962 women were assessed for eligibility and 317 women were randomized. Computerized randomization with concealed allocation was performed in the proportions 1:1 to one of two groups: weight reduction intervention followed by IVF-treatment or IVF-treatment only. One cycle per patient was included. PARTICIPANTS/MATERIALS, SETTING, METHODS: Nine infertility clinics in Sweden, Denmark and Iceland participated. Women under 38 years of age planning IVF, and having a BMI ≥30 and <35 kg/m2 were randomized to two groups: an intervention group (160 patients) with weight reduction before IVF, starting with 12 weeks of a low calorie liquid formula diet (LCD) of 880 kcal/day and thereafter weight stabilization for 2-5 weeks, or a control group (157 patients) with IVF only. MAIN RESULTS AND ROLE OF CHANCE: In the full analysis set (FAS), the live birth rate was 29.6% (45/152) in the weight reduction and IVF group and 27.5% (42/153) in the IVF only group. The difference was not statistically significant (difference 2.2%, 95% CI: 12.9 to -8.6, P = 0.77). The mean weight change was -9.44 (6.57) kg in the weight reduction and IVF group as compared to +1.19 (1.95) kg in the IVF only group, being highly significant (P < 0.0001). Significantly more live births were achieved through spontaneous pregnancies in the weight reduction and IVF group, 10.5% (16) as compared to the IVF only group 2.6% (4) (P = 0.009). Miscarriage rates and gonadotropin dose used for IVF stimulation did not differ between groups. Two subgroup analyses were performed. The first compared women with PCOS in the two randomized groups, and the second compared women in the weight reduction group reaching BMI ≤ 25 kg/m2 or reaching a weight loss of at least five BMI units to the IVF only group. No statistical differences in live birth rates between the groups in either subgroup analysis were found. LIMITATIONS, REASON FOR CAUTION: The study was not powered to detect a small increase in live births due to weight reduction and was not blinded for the patients or physician. Further, the intervention group had a longer time to achieve a spontaneous pregnancy, but were therefore slightly older than the control group at IVF. The study only included women with a BMI lower than 35 kg/m2. WIDER IMPLICATIONS OF THE FINDINGS: The study suggests that weight loss for obese women (BMI: 30-34.9 kg/m2) may not rectify the outcome in IVF cycles, although a significant higher number of spontaneous conceptions occurred in the weight loss group. Also, the study suggests that intensive weight reduction with LCD treatment does not negatively affects the results. STUDY FUNDING/COMPETING INTEREST(S): The study was funded by Sahlgrenska University Hospital (ALFGBG-70 940), Merck AB, Solna, Sweden (an affiliate of Merck KGaA, Darmstadt, Germany), Impolin AB, Hjalmar Svensson Foundation and Jane and Dan Olsson Foundation. Dr Thurin-Kjellberg reports grants from Merck, non-financial support from Impolin AB, during the conduct of the study, and personal fees from Merck outside the submitted work. Dr Friberg reports personal fees from Ferring, Merck, MSD, Finox and personal fees from Studentlitteratur, outside the submitted work. Dr Englund reports personal fees from Ferring, and non-financial support from Merck, outside the submitted work. Dr Bergh reports and has been reimbursed for: writing a newsletter twice a year (Ferring), lectures (Ferring, MSD, Merck), and Nordic working group meetings (Finox). Dr Karlström reports lectures (Ferring, Finox, Merck, MSD) and Nordic working group meetings (Ferring). Ms Kluge, Dr Einarsson, Dr Pinborg, Dr Klajnbard, Dr Stenlöf, Dr Larsson, Dr Loft and Dr Wistrand have nothing to disclose. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov number, NCT01566929. TRIAL REGISTRATION DATE: 23-03-2012. DATE OF FIRST PATIENT'S ENROLMENT: 05-10-2010.

Haemostatic reference intervals in pregnancy.

Haemostatic reference intervals are generally based on samples from non-pregnant women. Thus, they may not be relevant to pregnant women, a problem that may hinder accurate diagnosis and treatment of haemostatic disorders during pregnancy. In this study, we establish gestational age-specific reference intervals for coagulation tests during normal pregnancy. Eight hundred one women with expected normal pregnancies were included in the study. Of these women, 391 had no complications during pregnancy, vaginal delivery, or postpartum period. Plasma samples were obtained at gestational weeks 13-20, 21-28, 29-34, 35-42, at active labor, and on postpartum days 1 and 2. Reference intervals for each gestational period using only the uncomplicated pregnancies were calculated in all 391 women for activated partial thromboplastin time (aPTT), fibrinogen, fibrin D-dimer, antithrombin, free protein S, and protein C and in a subgroup of 186 women in addition for prothrombin time (PT), Owren and Quick PT, protein S activity, and total protein S and coagulation factors II, V, VII, VIII, IX, X, XI, and XII. The level of coagulation factors II, V, X, XI, XII and antithrombin, protein C, aPTT, PT remained largely unchanged during pregnancy, delivery, and postpartum and were within non-pregnant reference intervals. However, levels of fibrinogen, D-dimer, and coagulation factors VII, VIII, and IX increased markedly. Protein S activity decreased substantially, while free protein S decreased slightly and total protein S was stable. Gestational age-specific reference values are essential for the accurate interpretation of a subset of haemostatic tests during pregnancy, delivery, and puerperium.

Laboratory reference intervals during pregnancy, delivery and the early postpartum period.

BACKGROUND: Physiological changes during pregnancy may affect laboratory parameters. Reference values based on samples from non-pregnant women are not necessarily useful for clinical decisions during pregnancy. There is a need to establish reference values during pregnancy in order to recognize pathological conditions. METHODS: Eight hundred and one women with expected normal pregnancies were included in the study. Of these, 391 had no complications during pregnancy, delivery, or the early postpartum period. Blood samples were obtained at gestational weeks 13-20, 21-28, 29-34, 35-42, at labor, and 1 and 2 days postpartum. Reference intervals were calculated for 36 tests as recommended by the International Federation of Clinical Chemistry and Laboratory Medicine. RESULTS: Many tests showed such large variations indicating that gestational age-specific reference intervals were necessary. Other tests had different but stable values when compared to non-pregnant women. A minor decrease in albumin levels was observed. This was not only due to pregnancy-associated hemodilution, since other components with the same or a larger molecular diameter did not show a similar decrease. Many tests exhibited a broad distribution around vaginal delivery and in the early postpartum period. CONCLUSIONS: Only a few parameters were unaffected during uncomplicated pregnancy, delivery, and the early postpartum period suggesting that implementation of gestational age-specific reference intervals is necessary.