Vanishing twin syndrome among ART singletons and pregnancy outcomes.

STUDY QUESTION: Among babies born by ART, do singleton survivors of a vanishing twin have lower birth weight than other singletons? SUMMARY ANSWER: Vanishing twin syndrome (VTS) was associated with lower birth weight among ART singletons; a sibship analysis indicated that the association was not confounded by maternal characteristics that remain stable between deliveries. WHAT IS KNOWN ALREADY: Previous studies indicate that ART singletons with VTS have increased risk of adverse pregnancy outcomes, compared with other ART singletons. The potential contribution of unmeasured maternal background characteristics has been unclear. STUDY DESIGN, SIZE AND DURATION: This was a Norwegian population-based registry study, including 17 368 mothers with 20 410 ART singleton deliveries between January 1984 and December 2013. PARTICIPANTS/MATERIALS, SETTING, METHODS: The study population included 17 291 ART singletons without VTS, 638 ART singletons with VTS and 2418 ART singletons with uncertain vanishing twin status. We estimated differences in birth weight and gestational age comparing ART singletons with VTS first to all ART singletons without VTS, and subsequently to their ART siblings without VTS, using random- and fixed-effects linear regression, respectively. The corresponding comparisons for the associations with preterm birth and small for gestational age (SGA) were conducted using random-and fixed-effects logistic regression. The sibling analysis of preterm birth included 587 discordant siblings, while the sibling analysis of SGA included 674 discordant siblings. MAIN RESULTS AND THE ROLE OF CHANCE: ART singletons with VTS had lower birth weight when compared to all ART singletons without VTS, with an adjusted mean difference (95% CI) of -116 g (-165, -67). When we compared ART singletons with VTS to their ART singletons sibling without VTS, the adjusted mean difference was -112 g (-209, -15). ART singletons with VTS also had increased risk of being born SGA, with an adjusted odds ratio (OR) (95% CI) of 1.48 (1.07, 2.03) compared to all ART singletons without VTS, and 2.79 (1.12, 6.91) in the sibship analyses. ART singletons with VTS were also more likely to be born preterm, although this difference did not reach statistical significance. LIMITATIONS REASONS FOR CAUTION: We did not have information on maternal socio-economic status, but this factor is accounted for in the sibship analyses. We also had no information on whether fresh or frozen embryos were replaced. WIDER IMPLICATIONS OF THE FINDINGS: The reduction in birth weight and increased risk of SGA in ART singletons with VTS may suggest the presence of harmful intrauterine factors with long-term health impact. While vanishing twins are not routinely observed in naturally conceived pregnancies, loss of a twin is potentially a risk factor for the surviving foetus in any pregnancy. This could be further explored in large samples of naturally conceived pregnancies with the necessary information. STUDY FUNDING/COMPETING INTEREST(S): The authors of this study are supported in part by the UK Medical Research Council, US National Institute of Environmental Health Sciences and the Norwegian Research Council. The authors have no conflicts of interest. TRIAL REGISTRATION NUMBER: N/A.

Obstetric and neonatal outcome after oocyte donation in 106 women with Turner syndrome: a Nordic cohort study.

STUDY QUESTION: What are the obstetric and neonatal outcomes of deliveries after oocyte donation (OD) in women with Turner syndrome (TS)? SUMMARY ANSWER: Pregnancies among women with TS carry a substantial risk, particularly for hypertensive disorders. Potentially life-threatening complications occurred in 3.3% of pregnancies. The neonatal outcomes were generally reassuring, with similar rates of preterm birth and low birthweight (LBW) as after conventional IVF and better than previously reported in deliveries after OD in women with TS. WHAT IS KNOWN ALREADY: OD pregnancies in women with TS are known to be high-risk pregnancies. STUDY DESIGN, SIZE, DURATION: This retrospective cohort study included 106 women with TS who delivered after OD (n = 122 deliveries, n = 131 newborns) in three Nordic countries (Finland, Denmark, Sweden) between 1992 and 2011. PARTICIPANTS, SETTING AND METHODS: Women with TS who delivered after OD in three Nordic countries were identified (n = 110). Four women declined to participate or were lost to follow-up, thus 106 women were included in the study. The medical data from fertility clinics, antenatal clinics and the hospitals where the women had been treated and/or delivered were scrutinized. MAIN RESULTS AND THE ROLE OF CHANCE: In this cohort, the karyotype was 45,X in 44% of the women with TS. Ten women (9.4%) had a known cardiac defect before pregnancy. Single embryo transfer was performed in 70.3% of the cases and the multiple birth rate was 7.4%. In total, 35.0% of the pregnancies were associated with a hypertensive disorder including pre-eclampsia in 20.5%. Potentially life-threatening complications occurred in four pregnancies (3.3%), including one woman with aortic dissection, one with mild regurgitation of the tricuspid and mitral valve, one with a mechanical heart valve who developed HELLP syndrome (haemolysis, elevated liver enzymes, low platelets) and one who underwent a post-partum hysterectomy due to severe haemorrhaging. Neonatal outcomes were reassuring, with a preterm birth rate of 8.0% and LBW rate of 8.8% in singletons. Major birth defects were found in 3.8% of the children. The perinatal mortality was 2.3% (3/131), including a set of extremely preterm twins. LIMITATIONS, REASONS FOR CAUTION: Although this study was performed over a period of almost 20 years in three different countries, with a low drop-out rate and little missing data, much larger series are needed to assess rare events. This study also lacks an appropriate control group. WIDER IMPLICATIONS OF THE FINDINGS: This study suggests that cardiovascular evaluation before and during pregnancy may contribute to favourable obstetric outcomes in many cases. Maternal outcomes were in agreement with the literature while neonatal outcomes were generally better than previously reported. The outcomes were consistent across the three countries, supporting generalizability to similar populations.