High birth weight and large-for-gestational-age in singletons born after frozen compared to fresh embryo transfer, by gestational week: a Nordic register study from the CoNARTaS group.

STUDY QUESTION: When do the differences in birth weights become apparent between singletons born after frozen embryo transfer (FET) and fresh embryo transfer (fresh ET)? SUMMARY ANSWER: Mean birth weights after FET become significantly higher starting from gestational week (GW) 33 among boys and from GW 34 among girls. WHAT IS KNOWN ALREADY: In recent years, there has been a steep rise in recorded FET treatments, enabling widespread use of elective single embryo transfer, thus reducing the risks associated with multiple gestations. However, singletons born after FET are heavier and there is a higher risk of large-for-gestational-age (LGA) (birth weight > 90 percentiles) compared to fresh ET. In contrast, risk of small-for-gestational-age (SGA, birth weight < 10 percentiles) is lower in singletons born after FET compared to fresh ET. The reasons, timing and consequences of these differences remain largely unclear. There is limited evidence about whether this difference in growth develops before the last trimester of pregnancy. STUDY DESIGN, SIZE, DURATION: This retrospective Nordic register-based cohort study compared singletons born after FET (n = 17 500) to singletons born after fresh ET (n = 69 510) and natural conception (NC, n = 3 311 588). All live born singletons born between the years 2000 and 2015 in Denmark, Norway and Sweden at gestational age ≥22 weeks were included from the population-based Committee of Nordic ART and Safety (CoNARTaS) study population. PARTICIPANTS/MATERIALS, SETTING, METHODS: Children born after FET were compared to those born after fresh ET and NC for mean birth weight and proportion of LGA and SGA for each GW at birth. Chi-square test and tests for relative proportions were used to compare categorical variables and Student's t-test was used to compare continuous variables. Adjusted odds ratios (aORs) for LGA and SGA were calculated using logistic regressions, adjusting for year of birth, maternal age, parity, BMI, chronic hypertension, diabetes, smoking and offspring sex. MAIN RESULTS AND THE ROLE OF CHANCE: Mean birth weights were significantly higher after FET compared to fresh ET starting from GW 33 (range from 75 g to 228 g by week) for boys and starting from GW 34 (range from 90 g to 236 g by week) for girls. Boys born after FET had a significantly higher proportion of LGA (11.0-15.1%) at birth between GW 36 and 42, compared to those born after fresh ET (7.1-9.4%) (range from P < 0.001 to P = 0.048 by week). For girls born after FET, the difference was seen between GW 37 and 42 (10.6-13.4%) compared to those born after fresh ET (6.6-8.0%) (range from P < 0.001 to P = 0.009 by week).The proportion of SGA was significantly lower among boys born after FET (7.6-8.7%) compared to fresh ET (11.9-13.6%) between GW 36 and 42 (range from P < 0.001 to P = 0.016 by week). For girls born after FET, the difference was seen between GW 38 and 42 (7.0-9.3%) compared to those born after fresh ET (13.0-14.6%) (P < 0.001). The proportion of LGA (12.3-15.1%) was significantly higher for boys born after FET between GW 38 and 41 (P < 0.001) and for girls born after FET (12.6-13.4%) between GW 37 and 40 (range from P < 0.001 to P = 0.018 by week), compared to naturally conceived boys (9.7-9.9%) and girls (9.0-10.0%). All singletons born after FET had a higher risk of LGA compared to singletons born after fresh ET (aOR 1.87, 95% CI 1.76-1.98) and singletons born after NC (aOR 1.28, 95% CI 1.22-1.35). LIMITATIONS, REASONS FOR CAUTION: There may be residual confounding factors that we were not able to control for, most importantly the causes of preterm birth, which may also influence foetal growth. A further limitation is that we have no knowledge on growth patterns between implantation and GW 22. Finally, the number of children born extremely preterm or post-term was limited even in this large study population. WIDER IMPLICATIONS OF THE FINDINGS: This is, to date, the largest study on birth weights among preterm and term ART singletons with a population-based design and NC control group. The results suggest that the freeze-thaw process is associated with higher birthweights and greater risk of LGA at least in the last trimester of pregnancy. This is an important aspect of the safety profile of ART. More research is needed on the long-term outcome of these children. STUDY FUNDING/COMPETING INTEREST(S): The CoNARTaS collaboration has received the following funding: the Nordic Trial Alliance: a pilot project jointly funded by the Nordic Council of Ministers and NordForsk [71450], the Central Norway Regional Health Authorities [46045000], the Norwegian Cancer Society [182356-2016], the Nordic Federation of Obstetrics and Gynaecology [NF13041, NF15058, NF16026 and NF17043], the Interreg Öresund-Kattegat-Skagerrak European Regional Development Fund (ReproUnion project) and the Research Council of Norway's Centre of Excellence funding scheme [262700]. None of the authors have any competing interests to declare. TRIAL REGISTRATION NUMBER: ISRCTN11780826.

Imprinting disorders in children born after ART: a Nordic study from the CoNARTaS group.

STUDY QUESTION: Is the risk of imprinting disorders increased in children conceived after ART? SUMMARY ANSWER: We found an adjusted odds ratio (AOR) of 2.84 [95% CI: 1.34-6.01] for Beckwith-Wiedemann syndrome in ART children, while the risk of Prader-Willi syndrome, Silver-Russell syndrome or Angelman syndrome was not increased in children conceived after ART. WHAT IS KNOWN ALREADY: Earlier studies, most of them small, have suggested an association between ART and imprinting disorders. STUDY DESIGN, SIZE, DURATION: This was a binational register-based cohort study. All children conceived by ART in Denmark (n = 45 393, born between 1994 and 2014) and in Finland (n = 29 244, born between 1990 and 2014) were identified. The full background populations born during the same time periods in the two countries were included as controls. Odds ratios of imprinting disorders in ART children compared with naturally conceived (NC) children were calculated. The median follow-up time was 8 years and 9 months for ART children and 11 years and 9 months for NC children. PARTICIPANTS/MATERIALS, SETTING, METHODS: From the national health registries in Denmark and Finland, we identified all children diagnosed with Prader-Willi syndrome (n = 143), Silver-Russell syndrome (n = 69), Beckwith-Wiedemann syndrome (n = 105) and Angelman syndrome (n = 72) born between 1994/1990 and 2014, respectively. MAIN RESULTS AND THE ROLE OF CHANCE: We identified a total of 388 children diagnosed with imprinting disorders; 16 of these were conceived after ART. The overall AOR for the four imprinting disorders in ART children compared with NC children was 1.35 [95% CI: 0.80-2.29], but since eight ART children were diagnosed with Beckwith-Wiedemann syndrome, the AOR for this specific imprinting disorder was 2.84 [95% CI: 1.34-6.01]. The absolute risk of Beckwith-Wiedemann syndrome in children conceived after ART was still low: 10.7 out of 100 000 newborns. The risks of Prader-Willi syndrome, Silver-Russell syndrome and Angelman syndrome were not increased in children conceived after ART. LIMITATIONS, REASONS FOR CAUTION: Imprinting disorders are rare events and our results are based on few ART children with imprinting disorders. The aetiology is complex and only partly clarified, and the clinical diagnoses are challenged by a broad phenotypic spectrum. WIDER IMPLICATIONS OF THE FINDINGS: In the existing studies, results on the risk of imprinting disorders in children conceived after ART are ambiguous. This study adds that the risk of imprinting disorders in ART children is very small and perhaps restricted to Beckwith-Wiedemann syndrome. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the Nordic Trial Alliance: a pilot project jointly funded by the Nordic Council of Ministers and NordForsk (grant number: 71450), the Nordic Federation of Obstetrics and Gynecology (grant numbers: NF13041, NF15058, NF16026 and NF17043) and the Interreg Öresund-Kattegat-Skagerak European Regional Development Fund (ReproUnion project). The authors have no conflicts of interest related to this work. TRIAL REGISTRATION NUMBER: N/A.

Obstetric and perinatal risks in 4601 singletons and 884 twins conceived after fresh blastocyst transfers: a Nordic study from the CoNARTaS group.

STUDY QUESTION: Are obstetric and perinatal outcomes in pregnancies after fresh blastocyst transfer (BT) comparable with those born after fresh cleavage stage transfer (CT) and spontaneous conception (SC)? SUMMARY ANSWER: Fresh BT is associated with a higher risk of placental and perinatal complications. WHAT IS KNOWN ALREADY: BT optimizes the selection of top-quality embryos and increases pregnancy and live birth rates per transfer compared to CT. However, concerns have been raised as extended culture duration may increase obstetric complications and impair perinatal outcomes. Previous studies have shown a higher risk of preterm birth (PTB) among infants born after BT compared with CT. Pregnancies after BT are also prone to a higher risk of same-sex twins after single embryo transfer (SET). STUDY DESIGN, SIZE, DURATION: A retrospective register-based cohort study used data from Denmark, Norway and Sweden including three cohorts: 56 557 singletons and 16 315 twins born after fresh IVF/ICSI cycles and 2 808 323 SC singletons in Denmark (birth years 1997-2014), Norway (2010-2015) and Sweden (2002-2015). Of the fresh IVF/ICSI singletons, 4601 were born after BT and 51 956 after CT. The twin cohort consisted of 884 fresh IVF/ICSI children born after BT and 15 431 fresh IVF/ICSI children born after CT. PARTICIPANTS/MATERIALS, SETTING, METHODS: Data were obtained from a large Nordic cohort of children born after ART and SC initiated by the Committee of Nordic ART and Safety (CoNARTaS). The CoNARTaS cohort was established by cross-linking National ART-, Medical Birth-, and National Patients Registers using the unique personal identification number, allocated to every citizen in the Nordic countries. Obstetric and perinatal outcomes after BT, CT and SC were compared using logistic regression analysis. For perinatal outcomes, we calculated gestational age based on the date of oocyte pick-up (OPU) and in sensitivity analyses on data from Denmark and Norway, we also calculated gestational age based on the second-trimester ultrasonography (US) scan. Risk of pregnancies with same-sex twins after SET was used as a proxy for risk of monozygotic twins. Adjustments were made for child's sex, birth year, parity (0 or >1), maternal age, body mass index, smoking, educational level, fertilization method (IVF/ICSI), the number of aspirated oocytes, SET and country. Information on educational level and the number of aspirated oocytes was not available for Norway. Children born after frozen embryo transfer were not included. The birth cohorts were restricted according to the year in which BT was introduced in the different countries. MAIN RESULTS AND THE ROLE OF CHANCE: A higher risk of placenta previa was found in singleton pregnancies after BT compared with CT (adjusted odds ratio [aOR] 2.11 [95% CI 1.76; 2.52]). Singletons born after BT had a higher risk of PTB (aOR 1.14 [95% CI 1.01; 1.29]) compared with CT singletons, when estimated based on OPU. Furthermore, an altered male/female ratio (aOR 1.13 [95% CI 1.06; 1.21]) with more males following BT compared with CT was seen. Risk of same-sex twins after SET was higher after single BT compared with single CT (aOR 1.94 [95% CI 1.42; 2.60]). LIMITATIONS, REASONS FOR CAUTION: Residual confounding cannot be excluded, in particular related to duration and cause of infertility that we could not adjust for due to lack of reliable data. WIDER IMPLICATIONS OF THE FINDINGS: Extended embryo culture to the blastocyst stage has the potential to compromise obstetric and perinatal outcomes in fresh cycles. These results are important since an increasing number of IVF/ICSI treatments are performed as BT. STUDY FUNDING/COMPETING INTEREST(S): NORDFORSK (project no: 71450). The Research Fund of Rigshospitalet, Copenhagen University Hospital. ReproUnion Collaborative study, co-financed by the European Union, Interreg V ÖKS. Grants from Swedish state under the agreement between the Swedish government and the county councils, the ALF-agreement (LUA/ALF 70940), Hjalmar Svensson Research Foundation. The Research Council of Norway through its Centres of Excellence funding scheme, project number 262700. None of the authors has any conflicts of interests to declare regarding this study. TRIAL REGISTRATION NUMBER: ISRCTN11780826.

Cumulative live birth rate prognosis based on the number of aspirated oocytes in previous ART cycles.

STUDY QUESTION: Is the number of aspirated oocytes in the first ART cycle associated with the cumulative live birthrates (CLBR) in subsequent cycles? SUMMARY ANSWER: The number of aspirated oocytes in the first cycle was associated with CLBR in subsequent cycles. Previous treatment response predicts outcome in future cycles. WHAT IS KNOWN ALREADY: Previous reports have shown a positive association between the number of retrieved oocytes and live birthrate per fresh treatment cycle. This has also been shown for the CLBR in one complete ART-cycle, including possible subsequent frozen-thawed transfers (FER). It has been shown that women with less than five oocytes in the first cycle have poorer outcome within six complete cycles than women with more than 12 oocytes, suggesting that the number of aspirated oocytes in the first cycle may be reproduced in later cycles. However, other studies have shown that an initial low treatment response may be improved with increased gonadotrophin start-dose. STUDY DESIGN, SIZE, DURATION: The Danish National IVF-registry includes all ART treatments in public and private clinics since 1994. Treatment-cycles were cross-linked with the Medical Birth Registry, identifying treatment-related births and natural conception births. This national cohort study includes all women starting ART treatments with homologous eggs between 2002 and 2011, N = 30 486. Subjects were followed for up to four fresh ART-cycles including subsequent FER-cycles (=four complete cycles), until the first livebirth, or until December 2011. PARTICIPANTS/MATERIALS, SETTING, METHODS: The CLBR within 1-4 complete ART-cycles were calculated as the proportion of women with a livebirth, out of all women initiating ART-treatment, including drop-outs (no livebirth or no continued treatment within follow-up). In women with one year follow-up from last treatment, multivariate logistic regression analysis assessed impact of retrieved oocytes on CLBR, adjusting results for female age and cause of infertility. Hospital admission due to ovarian hyperstimulation syndrome (OHSS) was reported. MAIN RESULTS AND THE ROLE OF CHANCE: After one, two and three complete ART-cycles, the CLBRs attributable to ART treatment were 26.4% [95%CI 25.9-26.9], 42.6% [42.0-43.1] and 51.3% [50.7-51.9], respectively. The CLBR attributable to non-ART related conception (natural conception or intrauterine insemination) were 5.3% [5.0-5.6], 8.3% [8.0-8.7] and 10.6% [10.3-11.0], after one, two and three complete cycles. In women without a live birth in the first complete cycle, the number of aspirated oocytes predicted the outcome in the second and third cycle: When compared to women with 0-3 aspirated oocytes in the first cycle, the odds for live birth in the second and third cycle was 1.18 [1.07-1.30] for women with 4-9 aspirated oocytes in the first cycle, 1.41 [1.27-1.57] for women with 10-15 aspirated oocytes and 1.63 [1.42-1.88] for women with more than 15 aspirated oocytes. For women without a livebirth in the first and second cycle, the sum of aspirated oocytes predicted outcome in the third complete cycle. Women with a sum larger than six aspirated oocytes, had marked increased odds ratios for livebirth in the third complete cycle, compared to women with a sum of 0-6 oocytes in the first and second fresh cycle. Incidence of hospital-admission due to OHSS was 1.7% in the first cycle, decreasing to 1.3% and 1.0% in the second and third cycles. LIMITATIONS, REASONS FOR CAUTION: Although mandatory, there may be treatment-cycles not registered in the IVF-registry. Missing information in number of aspirated oocytes are most likely random losses of information. There were few observations in women with more than 15 aspirated oocytes and these birthrates should be interpreted cautiously. Information on gonadotrophin dose used for stimulation was not available, nor was information on dose adjustments in subsequent cycles. WIDER IMPLICATIONS OF THE FINDINGS: With these results we can counsel couples returning for fertility treatments, providing an age-stratified revised prognosis for chances of live birth and risk of OHSS, reflecting prior failed attempts and previous ovarian response. STUDY FUNDING/COMPETING INTEREST(S): This study was unconditionally funded by Ferring Pharmaceuticals and ReproUnion. The funders had no role in the study design, data collection and interpretation, or decision to submit the work for publication. The authors have no conflicts of interest. TRIAL REGISTRATION NUMBER: The study was approved by the Danish Data Protection Agency (J.nr. 2012-41-1330).

Academic performance in adolescents aged 15-16 years born after frozen embryo transfer compared with fresh embryo transfer: a nationwide registry-based cohort study.

OBJECTIVE: To assess academic performance in singletons aged 15-16 years conceived after frozen embryo transfer (FET) compared with singletons born after fresh embryo transfer (ET) in Danish cohorts born from 1995 to 2001. DESIGN: Danish national registry-based cohort study. SETTING: Danish national registries. POPULATION: All 6495 singletons conceived after assisted reproductive technology (ART) treatment in Denmark from 1995 to 2001 [FET (n) = 423; fresh ET (n) = 6072]. METHODS: Mean test scores on a national standardised and international comparable grading-scale. Comparisons of test score were first made in univariate analysis (Model 1) and secondly in a multivariate linear model (Model 2) adjusting for relevant reproductive and socio-demographic covariates such as the occupational and educational level of the parents. Sensitivity analyses on FET-IVF (in vitro fertilisation) versus fresh ET-IVF and FET-ICSI (intracytoplasmic sperm injection) versus fresh ET-ICSI were made. Linear mixed models were used to account for the correlation in test scores of siblings for continuous outcome. MAIN OUTCOME MEASURES: Mean overall test score and test score in Danish, mathematics, English, and physics/chemistry. RESULTS: Crude and adjusted mean test scores were similar for adolescents conceived after FET compared with fresh ET. The crude mean difference was +0.11 (95% CI -0.11; 0.34), and the adjusted mean difference was +0.12 (95% CI -0.09; 0.34). CONCLUSIONS: Adolescents conceived after FET had similar academic performance at 15-16 of years of age compared with children conceived after fresh ET. TWEETABLE ABSTRACT: Using frozen embryos in fertility treatment does not affect school performance in Danish adolescents aged 15-16 years.

The long-term prognosis for live birth in couples initiating fertility treatments.

STUDY QUESTION: What are the long-term chances of having a child for couples starting fertility treatments and how many conceive with ART, IUI and without treatment? SUMMARY ANSWER: Total 5-year live birthrates were strongly influenced by female age and ranged from 80% in women under 35-26% in women ≥40 years, overall, 14% of couples conceived naturally and one-third of couples starting treatments with intrauterine insemination delivered from that treatment. WHAT IS KNOWN ALREADY: Few studies report success rates in fertility treatments across a couple's complete fertility treatment history, across clinics, evaluating live births after insemination, ART and natural conceptions. STUDY DESIGN, SIZE, DURATION: This register-based national cohort study from Denmark includes all women initiating fertility treatments in public and private clinics with homologous gametes in 2007-2010. PARTICIPANTS/MATERIALS, SETTING, METHODS: Women were identified in the Danish ART Registry and were cross-linked with the Medical Birth Registry to identify live births. Subfertile couples were followed 2 years (N = 19 884), 3 years (N = 14 445) and 5 years (N = 5165), or until their first live birth. Cumulative live birthrates were estimated 2, 3 and 5 years from the first treatment cycle, in all women, including drop-outs. Birthrates were stratified by type of first treatment (ART/IUI), mode of conception (ART/IUI/natural conception) and female age. MAIN RESULTS AND THE ROLE OF CHANCE: Within 5 years, in women aged <35 years (N = 3553), 35-39 years (N = 1156) and ≥40 years (N = 451), a total of 64%, 49% and 16% had a live birth due to treatment, respectively. Additionally, in women aged < 35 years, 35-39 years and ≥40 years, 16%, 11% and 10% delivered after natural conception, yielding total 5-year birthrates of 80%, 60% and 26%. In women starting treatments with IUI (N = 3028), 35% delivered after IUI within 5 years, 24% delivered after shift to ART treatments and 17% delivered after natural conception. Within 5 years from starting treatments with ART (N = 2137), 53% delivered after ART, 11% delivered after natural conception and 0.6% delivered after IUI. LIMITATIONS, REASONS FOR CAUTION: Birthrates are most likely higher compared to countries without national coverage of treatments and results are influenced by laws and regulations. Information on duration of infertility prior to treatment was not available. Future prospective intervention studies should focus on the role of expectant management. WIDER IMPLICATIONS OF THE FINDINGS: Our results can provide couples with a comprehensible age-stratified prognosis at start of treatment. STUDY FUNDING/COMPETING INTEREST(S): This study was unconditionally funded by Ferring Pharmaceuticals and the Augustinus foundation. All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf and declare: S.S.M. received an unconditional grant from Ferring Pharmaceuticals; A.A.H. has received personal fees from Ferring Pharmaceuticals not related to this work; A.N.A. reports grants and personal fees from Ferring Pharmaceuticals, personal fees from Merck Serono, grants and personal fees from MSD, outside the submitted work; no financial relationships with any organizations that might have an interest in the submitted work in the previous 3 years; no other relationships or activities that could appear to have influenced the submitted work. TRIAL REGISTRATION NUMBER: The study was approved by the Danish Data Protection Agency (J.nr. 2012-41-1330).

Risk of hypertensive disorders in pregnancies following assisted reproductive technology: a cohort study from the CoNARTaS group.

STUDY QUESTION: Is the risk of hypertensive disorders in pregnancies conceived following specific assisted reproductive technology (ART) procedures different from the risk in spontaneously conceived (SC) pregnancies? SUMMARY ANSWER: ART pregnancies had a higher risk of hypertensive disorders, in particular following cryopreservation, with the highest risk seen in twin pregnancies following frozen-thawed cycles. WHAT IS KNOWN ALREADY: The risk of hypertensive disorders is higher in ART pregnancies than in SC pregnancies. The increased risk may be partly explained by multiple pregnancies and underlying infertility, but a contribution from specific ART procedures has not been excluded. STUDY DESIGN, SIZE, DURATION: Population-based cohort study, including sibling design with nationwide data from health registers in Sweden, Denmark and Norway. PARTICIPANTS/MATERIALS, SETTING, METHODS: All registered ART pregnancies and a sample of SC pregnancies with gestational age ≥22 weeks from 1988 to 2007 were included. ART singleton pregnancies (n = 47 088) were compared with SC singleton pregnancies (n = 268 599), matched on parity and birth year. ART twin pregnancies (n = 10 918) were compared with SC twin pregnancies (46 674). We used logistic regression to estimate adjusted odds ratios and risk differences for hypertensive disorders in pregnancies following IVF, ICSI and fresh or frozen-thawed cycles. We also compared fresh and frozen-thawed cycles within mothers who had conceived following both procedures using conditional logistic regression (sibling analysis). MAIN RESULTS AND THE ROLE OF CHANCE: Hypertensive disorders were reported in 5.9% of ART singleton and 12.6% of ART twin pregnancies. Comparing singleton pregnancies, the risk of hypertensive disorders was higher after all ART procedures. The highest risk in singleton pregnancies was seen after frozen-thawed cycles [risk 7.0%, risk difference 1.8%, 95% confidence interval (CI) 1.2-2.8]. Comparing twin pregnancies, the risk was higher after frozen-thawed cycles (risk 19.6%, risk difference 5.1%, 95% CI 3.0-7.1), but not after fresh cycles. In siblings, the risk was higher after frozen-thawed cycles compared with fresh cycles within the same mother (odds ratio 2.63, 95% CI 1.73-3.99). There were no clear differences in risk for IVF and ICSI. LIMITATIONS, REASONS FOR CAUTION: The number of ART siblings in the study was limited. Residual confounding cannot be excluded. In addition, we did not have information on all SC pregnancies in each woman's history, and could therefore not compare risk in ART versus SC pregnancies in the same mother. WIDER IMPLICATIONS OF THE FINDINGS: Pregnancies following frozen-thawed cycles have a higher risk of hypertensive disorders, also when compared with fresh cycle pregnancies by the same mother. The safety aspects in frozen-thawed cycles merit further attention. STUDY FUNDING/COMPETING INTERESTS: Funding was received from the European Society for Human Reproduction and Embryology, the University of Copenhagen, the Danish Agency for Science, Technology and Innovation, the Nordic Federation of Societies of Obstetrics and Gynecology and the Liaison Committee between the Central Norway Regional Health Authority and the Norwegian University of Science and Technology. None of the authors has any competing interests to declare.

Trends in perinatal health after assisted reproduction: a Nordic study from the CoNARTaS group.

STUDY QUESTIONS: Has the perinatal outcome of children conceived after assisted reproductive technology (ART) improved over time? SUMMARY ANSWER: The perinatal outcomes in children born after ART have improved over the last 20 years, mainly due to the reduction of multiple births. WHAT IS KNOWN AND WHAT THIS PAPER ADDS: A Swedish study has shown a reduction in unwanted outcomes over time in children conceived after ART. Our analyses based on data from more than 92 000 ART children born in four Nordic countries confirm these findings. STUDY DESIGN: Nordic population-based matched cohort study with ART outcome and health data from Denmark, Finland, Norway and Sweden. PARTICIPANTS, SETTING AND METHODS: We analysed the perinatal outcome of 62 379 ART singletons and 29 758 ART twins, born from 1988 to 2007 in four Nordic countries. The ART singletons were compared with a control group of 362 215 spontaneously conceived singletons. Twins conceived after ART were compared with all spontaneously conceived twins (n = 122 763) born in the Nordic countries during the study period. The rates of several adverse perinatal outcomes were stratified into the time periods: 1988-1992; 1993-1997; 1998-2002 and 2003-2007 and presented according to multiplicity. MAIN RESULTS AND ROLE OF CHANCE: For singletons conceived after ART, a remarkable decline in the risk of being born preterm and very preterm was observed. The proportion of ART singletons born with a low and very low birthweight also decreased. Finally, the stillbirth and infant death rates have declined among both ART singletons and twins. Throughout the 20 year period, fewer ART twins were stillborn or died during the first year of life compared with spontaneously conceived twins, presumably due to the lower proportion of monozygotic twins among the ART twins. LIMITATIONS, REASONS FOR CAUTION: We were not able to adjust for some potential confounders such as BMI, smoking, length or cause of infertility. The Nordic ART populations have changed over time, and in recent years, both less as well as severely reproductive ill couples are being treated. This may have affected the observed trends. WIDER IMPLICATIONS OF THE FINDINGS: It is assuring that data from four countries confirm an overall improvement over time in the perinatal outcomes of children conceived after ART. Furthermore, data show the beneficial effect of single embryo transfer, not only in regard to lowering the rate of multiples but also concerning the health of singletons. STUDY FUNDING/COMPETING INTERESTS: The European Society for Human Reproduction and Embryology (ESHRE), the University of Copenhagen and the Danish Agency for Science, Technology and Innovation has supported the project. The CoNARTaS group has received travel and meeting funding from the Nordic Federation of Obstetrics and Gynecology (NFOG). None of the authors has any competing interests to declare.

Follicle pool, ovarian surgery and the risk for a subsequent trisomic pregnancy.

STUDY QUESTION: Is there an association between trisomic pregnancy, a marker for decreased oocyte quality, and the reduced oocyte quantity that follows ovarian surgery? SUMMARY ANSWER: Previous ovarian surgery is not associated with an increased risk for a subsequent trisomic pregnancy. WHAT IS KNOWN ALREADY: Ovarian surgery diminishes the number of oocytes. The risk for a trisomic pregnancy is suggested to be higher in women with fewer oocytes, independent of their chronological age. STUDY DESIGN, SIZE, DURATION: This is a matched case-control study. Cases are women with a confirmed trisomic pregnancy occurring between 1 January 2000 and 31 December 2010 regardless of pregnancy outcome and controls are women that had a live born child without a trisomy. In total, there were 8573 participants in the study; 1723 cases and 6850 controls. PARTICIPANTS/MATERIALS, SETTING, METHODS: Data were obtained from Danish medical registries. Matching criteria were maternal age and year of conception. Number of controls matched per case ranged from one to four. Among cases and controls with a trisomic pregnancy, 2.7% (46/1723) versus 2.5% (172/6850) had undergone ovarian surgery before pregnancy. MAIN RESULTS AND ROLE OF CHANCE: History of ovarian surgery is not associated with a higher risk for a subsequent trisomic pregnancy (odds ratio = 1.00, 95% confidence interval 0.99-1.01). Subgroup analyses by indication of surgery and interval between ovarian surgery and pregnancy do not show an effect on trisomic pregnancy risk. LIMITATIONS, REASONS FOR CAUTION: The medical registries used to select cases and controls did not contain information on surgical technique nor volume of ovarian tissue resected, previous trisomic pregnancy prior to the ovarian surgery or long-term use of oral contraceptives. Therefore, correction for these factors was not performed. WIDER IMPLICATIONS OF THE FINDINGS: We did not confirm the hypothesis that ovarian surgery, a marker for decreased oocyte quantity, is related to trisomic pregnancy, a marker for decreased oocyte quality. This suggests that ovarian surgery, which has a direct reductive effect on the size of the follicle pool, may affect oocyte quality differently when compared with the reduction in follicle pool size due to ageing. STUDY FUNDING/COMPETING INTERESTS: The study was supported by grants from the Gratama Stichting, University of Groningen and the University Medical Center Groningen, The Netherlands. Ø.L. has within the last 3 years received honoraria for speeches in pharmacoepidemiological issues, not related to this study. The Department of Obstetrics and Gynaecology receives unrestricted educational grants from Ferring Pharmaceuticals. A.H. received a grant from ZonMW (i.e. National Dutch Scientific funding) for a RCT not related to this publication. Dr A.H. received speakers fee from MSD for an educational presentation. All other authors have no conflict of interest.

Risk of stillbirth and infant deaths after assisted reproductive technology: a Nordic study from the CoNARTaS group.

STUDY QUESTION: Is the risk of stillbirth and perinatal deaths increased after assisted reproductive technology (ART) compared with pregnancies established by spontaneous conception (SC)? SUMMARY ANSWER: A significantly increased risk of stillbirth in ART singletons was only observed before 28 + 0 gestational weeks. WHAT IS KNOWN ALREADY: The current literature indicates that children born after ART have an increased risk of perinatal death. The knowledge on stillbirth in ART pregnancies is limited. STUDY DESIGN, SIZE, DURATION: A population based case-control study. PARTICIPANTS/MATERIALS, SETTING AND METHODS: A total of 62 485 singletons and 29 793 twins born after ART in Denmark, Finland, Norway and Sweden, from 1982 to 2007, were compared with 362 798 spontaneously conceived (SC) singletons and 132 181 twins. MAIN RESULTS AND THE ROLE OF CHANCE: The adjusted rate ratio for stillbirth at gestational weeks 22 + 0 to 27 + 6 was 2.08 [95% confidence interval (CI) 1.55-2.78] for ART versus SC singletons. After 28 + 0 gestational weeks there was no significant difference in the risk of stillbirth between ART and SC singletons. ART twins had a lower risk of stillbirth compared with SC twins, but when restricting the analysis to opposite-sex twins and excluding all monozygotic twins, there was no significant difference between the groups. Singletons conceived by ART had an overall increased risk of early neonatal death (adjusted odds ratio 1.54, 95% CI 1.28-1.85) and death within the first year after birth (1.45, 1.26-1.68). No difference regarding these two parameters was found when further adjusting for the gestational age [(0.97, 0.80-1.18) and (0.99, 0.85-1.16), respectively]. ART twins had a lower risk of early neonatal and infant deaths than SC twins, but no difference was found when restricting the analyses to opposite-sex twins. LIMITATIONS, REASON FOR CAUTION: We were not able to adjust for potential confounders, such as a prior history of stillbirth, induction of labour, body mass index or smoking. WIDER IMPLICATIONS OF THE FINDINGS: The risk of stillbirth in ART versus SC singletons was only increased for very early gestational ages (before 28 weeks). This might indicate that the current clinical management of ART pregnancies is sufficient regarding prevention of stillbirth during the third trimester. STUDY FUNDING/COMPETING INTEREST(S): No conflict of interest was reported. The European Society for Human Reproduction and Embryology (ESHRE), the University of Copenhagen, Denmark, the Danish Agency for Science, Technology and Innovation and Sahlgrenska University Hospital, Gothenburg, Sweden supported the project. The CoNARTaS group has received travel and meeting funding from the Nordic Society of Obstetrics and Gynecology (NFOG).

Large baby syndrome in singletons born after frozen embryo transfer (FET): is it due to maternal factors or the cryotechnique?

STUDY QUESTION: Are singletons born after frozen embryo transfer (FET) at increased risk of being born large for gestational age (LGA) and if so, is this caused by intrinsic maternal factors or related to the freezing/thawing procedures? SUMMARY ANSWER: Singletons after FET have an increased risk of being born LGA. This cannot solely be explained by intrinsic maternal factors as it was also observed in sibling pairs, where the sibling conceived after FET had an increased risk of LGA compared with the sibling born after Fresh embryo transfer. WHAT IS KNOWN ALREADY: FET singletons have a higher mean birthweight than singletons born after transfer of fresh embryos, and FET singletons may be at an increased risk of being born LGA. STUDY DESIGN, SIZE, DURATION: The national register-based controlled cohort study involves two populations of FET singletons. The first population (A: total FET cohort) consisted of all FET singletons (n = 896) compared with singletons born after Fresh embryo transfer (Fresh) (n = 9480) and also with that born after natural conception (NC; n = 4510) in Denmark from 1997 to 2006. The second population (B: Sibling FET cohort) included all sibling pairs, where one singleton was born after FET and the consecutive sibling born after Fresh embryo transfer or vice versa from 1994 to 2008 (n = 666). The sibling cohort included n = 550 children with the sibling combination first child Fresh/second child FET and n = 116 children with the combination first child FET/second child Fresh. PARTICIPANTS/MATERIALS, SETTING, METHODS: Main outcome measures were LGA defined as birthweight of >2 SD from the population mean (z-score >2) according to Marsáls curves. Macrosomia was defined as birthweight of >4500 g. Crude and adjusted odds ratios (AORs) of LGA and macrosomia were calculated for FET versus Fresh and versus NC singletons in the total FET cohort. Similarly, AOR was calculated for FET versus Fresh in the sibling cohort. Adjustments were made for maternal age, parity, child sex, year of birth and birth order in the sibling analyses. Meta-analyses were performed by pooling our data with the previously published cohort studies on LGA and macrosomia. MAIN RESULTS AND THE ROLE OF CHANCE: The AORs of LGA (z-score >2) and macrosomia in FET singletons versus singletons conceived after Fresh embryo transfer were 1.34 [95% confidence interval (95% CI) 0.98-1.80] and 1.91 (95% CI 1.40-2.62), respectively. The corresponding risks for FET versus NC singletons were 1.41 (95% CI 1.01-1.98) for LGA and 1.67 (95% CI 1.18-2.37) for macrosomia. The increased risk of LGA and macrosomia in FET singletons was confirmed in the sibling cohort also after adjustment for birth order. Hence, the increased risk of LGA in FET singletons cannot solely be explained by being the second born or by intrinsic maternal factors, but may also partly be related to freezing/thawing procedures per se. In the meta-analysis, the summary effects of LGA and macrosomia in FET versus singletons conceived after Fresh embryo transfer were AOR 1.54 (95% CI 1.31-1.81) and AOR 1.64 (95% CI 1.26-2.12), respectively. The corresponding figures for FET versus NC singletons were for LGA AOR 1.32 (95% CI 1.07-1.61) and macrosomia AOR 1.41 (95% CI 1.11-1.80), respectively. LIMITATIONS, REASONS FOR CAUTION: Adjustment for body mass index as a possible confounder was not possible. The size of the FET/Fresh sibling cohort was limited; however, the complete sibling cohort was sufficiently powered to explore the risk of LGA. A bias is very unlikely as data coding was based on national registers. WIDER IMPLICATIONS OF THE FINDINGS: Our findings are consistent with the previous Nordic studies and thus can be generalized to the Nordic countries. The causes for LGA in FET singletons should be further explored. STUDY FUNDING/COMPETING INTEREST(S): No external funding was used for this project. None of the authors have any conflict of interest to declare.