Background: Evidence referring to the trade-offs between the benefits and risks of single embryo transfer (SET) versus double embryo transfer (DET) following assisted reproduction technology are insufficient, especially for those women with a defined embryo quality or advanced age.Methods: A systematic review and meta-analysis was conducted according to PRISMA guidelines. PubMed, EMBASE, Cochrane Library andClinicalTrials.govwere searched based on established search strategy from inception through February 2021. Pre-specified primary outcomes were live birth rate (LBR) and multiple pregnancy rate (MPR). Odds ratio (OR) with 95% confidence interval (CI) were pooled by a random-effects model using R version 4.1.0.Results: Eighty-five studies (14 randomized controlled trials and 71 observational studies) were eligible. Compared with DET, SET decreased the probability of a live birth (OR = 0.78, 95% CI: 0.71–0.85,P < 0.001,n = 62), and lowered the rate of multiple pregnancy (0.05, 0.04–0.06,P < 0.001,n = 45). In the sub-analyses of age stratification, both the differences of LBR (0.87, 0.54–1.40,P = 0.565,n = 4) and MPR (0.34, 0.06–2.03,P = 0.236,n = 3) between SET and DET groups became insignificant in patients aged ≥40 years. No significant difference in LBR for single GQE versus two embryos of mixed quality [GQE + PQE (non-good quality embryo)] (0.99, 0.77–1.27,P = 0.915,n = 8), nor any difference of MPR in single PQE versus two PQEs (0.23, 0.04–1.49,P = 0.123,n = 6). Moreover, women who conceived through SET were associated with lower risks of poor outcomes, including cesarean section (0.64, 0.43-0.94), antepartum haemorrhage (0.35, 0.15-0.82), preterm birth (0.25, 0.21-0.30), low birth weight (0.20, 0.16-0.25), Apgar1 < 7 rate (0.12, 0.02-0.93) or neonatal intensive care unit admission (0.30, 0.14-0.66) than those following DET.Conclusions: In women aged < 40 years or if any GQE is available, SET should be incorporated into clinical practice. While in the absence of GQEs, DET may be preferable. However, for elderly women aged ≥40 years, current evidence is not enough to recommend an appropriate number of embryo transfer. The findings need to be further confirmed.

Hypertensive disorders of pregnancy is a prevalent pregnancy complication worldwide, and the dose-response association between maternal pre-pregnancy body mass index (BMI) and hypertensive disorders of pregnancy has not been precisely studied. The aim of this study was to assess dose-response association between maternal pre-pregnancy BMI and hypertensive disorders of pregnancy, including pregnancy induced hypertension, preeclampsia and eclampsia. This dose-response meta-analysis searched four electronic databases (Pubmed, Web of science, OVID Embase and OVID Medline) for relevant publications up to October, 2023. Cohort studies evaluated the association between pre-pregnancy or early pregnancy maternal BMI and pregnancy induced hypertension, preeclampsia, eclampsia and hypertensive disorders of pregnancy were included. Non-linear or linear dose-response association was modeled. Unadjusted and adjusted effects were pooled separately, and four subgroups, meta-regression, five sensitivity analyses were conducted. Study protocol was registered on the PROSPERO (CRD42022290318). 157 cohort studies involving 51,813,975 pregnancies were finally included. Of 157 studies, multiple outcomes were reported: 58 on pregnancy induced hypertension, 92 on preeclampsia, 6 on eclampsia, and 84 on hypertensive disorders of pregnancy, have assessed the association with pre-pregnancy BMI. A significant linear dose-response relationship was identified between BMI and pregnancy induced hypertension with a crude relative risk (cRR) of BMI per 5-unit increase of 1.73 (95% confidence intervals [CI]: 1.65–1.81), and an adjusted odds ratio (aOR) per 5-unit increase of 1.82 (95% CI: 1.74–1.90). Similar dose-response relationship was observed between BMI and preeclampsia (cRR: 1.63, 1.58–1.69; aOR: 1.70, 1.61–1.80), eclampsia (cRR: 1.40, 1.28–1.53; aOR: 1.36, 1.20–1.53) and hypertensive disorders of pregnancy (cRR: 1.68, 1.63–1.74; aOR: 1.75, 1.68–1.82). Subgroup analyses revealed that the pooled risk of BMI for pregnancy induced hypertension, preeclampsia, eclampsia, and hypertensive disorders of pregnancy was likely higher in Asian pregnant women compared to those in American and European regions. Sensitivity analyses results were mainly consistent with the primary results. This meta-analysis demonstrated a clear and significant dose-response relationship between increasing maternal pre-pregnancy BMI and elevated risks of pregnancy induced hypertension, preeclampsia, eclampsia, and overall hypertensive disorders of pregnancy, underscoring the clinical importance of maintaining a healthy BMI prior to conception. Pre-pregnancy BMI may be an important focus for preconception counseling and subsequent pre-pregnancy weight management for both clinicians and women. 10.13039/501100001809 National Natural Science Foundation of China (72174132, 82474335, 82225049), 10.13039/501100018542 Natural Science Foundation of Sichuan Province (2024NSFSC1668, 2024YFFK0152), 1.3.5 project for disciplines of excellence, 10.13039/501100013365 West China Hospital, Sichuan University (ZYGD23004).

Aims/Introduction: To evaluate gestational weight gain (GWG) in the first and second trimester as a risk factor for gestational diabetes mellitus (GDM) among women pregnant with singletons.Materials and Methods: This was a cohort study of women with singleton pregnancies who delivered between 1 January 2013 and 31 October 2014 in a Chinese hospital. We collected data from medical records from the first antenatal visit to delivery. All pregnant women were subjected to an oral glucose tolerance test for diagnosis of GDM during the second trimester. GWG in the first and second trimester was calculated by subtracting the prepregnancy weight from weight within 4 weeks of the oral glucose tolerance test. We categorized GWG into insufficient, appropriate and excessive according to the Institute of Medicine guidelines and population quantiles. Univariable and multivariable analyses were used to determine the association between GWG and GDM risk.Results: Of 10,422 pregnant women, we identified 8,356 eligible women with 1,622 (19.4%) diagnosed with GDM. Univariable analysis showed that GWG that exceeded the Institute of Medicine recommendation might be associated with risk of GDM (P < 0.05), but this association was not observed by multivariable analysis (adjusted odds ratio 1.07, [95% confidence interval 0.94–1.21]). Univariable and multivariable analyses both showed that GWG exceeding the 90th and 95th quantiles of included women, respectively, were at increased risk for GDM (adjusted odds ratio >P₉₀ vs P₁₀–P₉₀ adjusted odds ratio 1.31, [95% confidence interval 1.12–1.52]; >P₉₅ vs P₅‐P₉₅ adjusted odds ratio 1.45 [95% confidence interval 1.16–1.81]).Conclusions: Excessive GWG in the first and second trimester might be a risk factor for GDM, which highlights the importance of appropriate weight gain during pregnancy.