Elective single embryo transfer and perinatal outcomes: a systematic review and meta-analysis
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OBJECTIVE: To determine whether elective single embryo transfer (eSET) lowers the risk of poor perinatal outcomes associated with IVF, when  compared with double embryo transfer (DET) or multiple embryo transfer (MET), and separately,  compared with spontaneous conceptions. DESIGN: Systematic review and meta-analysis. SETTING: Centers for reproductive care. PATIENT(S): Infertility patients. INTERVENTION(S): MEDLINE, Embase, and bibliographies were searched for the period 1978-2011. Two reviewers independently assessed titles, abstracts, and full studies, extracted data, and assessed quality. Dichotomous data were pooled using relative risks and continuous data with mean differences using a random effects model. Randomized controlled trials (RCTs), case-control studies, and cohort studies that examined any of the primary or secondary outcomes in singleton, twin, or multiple-order infants conceived by eSET as compared with  those conceived by DET or MET or  spontaneously conceived singleton gestations were included. MAIN OUTCOME MEASURE(S): Primary outcomes were preterm birth (PTB, <37 weeks' gestation) and low birth weight (LBW, <2,500 g). RESULT(S): Sixteen studies were included (eight RCTs, eight cohort studies). Compared with DET-conceived infants, eSET-conceived singletons were less likely to be born either preterm (RCT-based relative risk [RR] 0.37, 95% confidence interval [CI] 0.25-0.55) or with LBW (RCT-based RR 0.25, 95% CI 0.15-0.45; cohort study RR 0.51, 95% CI 0.29-0.91). However, compared with spontaneously conceived singletons, eSET gestations had higher risks of PTB (RR 2.13, 95% CI 1.26-3.61), placenta previa (RR 6.02, 95% CI 2.79-13.01), gestational diabetes (RR 1.69, 95% CI 1.19-2.42), and ectopic pregnancy (RR 6.40, 95% CI 4.38-9.35). CONCLUSION(S): Elective single embryo transfer is associated with decreased risks of PTB and LBW compared with DET but higher risks of PTB compared with spontaneously conceived singletons.
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