LAUSR

OBJECTIVE To conduct a systematic review and meta-analyses of literature regarding the risk of preterm birth in singleton pregnancies following a prior preterm twin birth. DATA SOURCES We conducted a literature search of Embase, Ovid Medline and Cochrane from inception until February 28, 2019. STUDY ELIGIBILITY CRITERIA Studies evaluating women with a prior twin birth followed by a singleton birth were included. STUDY APPRAISAL AND SYNTHESIS METHODS Data were abstracted in duplicate and summary odds ratios (OR) and confidence intervals (CI) were calculated using random effects model. Risk of bias was assessed using Newcastle-Ottawa Scale and quality of evidence was evaluated using GRADE. The primary outcome was a preterm singleton birth (<37 weeks gestational age), secondary outcomes included risk of late preterm birth (34 to 366 weeks), preterm birth between 30 and 336 and preterm birth less than 30 weeks. Sub-analysis of risk of singleton preterm birth after spontaneous twin birth was also performed. A priori, the protocol was developed and registered with PROSPERO (Registration number: CRD42017053382). RESULTS Eight cohort studies at low risk-of-bias met inclusion criteria for systematic review and six for the meta-analysis. Compared to women with previous term twin births, women who had previous preterm (<37 weeks gestation) twin births were at increased odds of preterm singleton birth in subsequent pregnancy OR 4.34 (95% CI, 2.83-6.65). Gestational age at birth of previous twin pregnancy was an effect modifier. Compared to previous term twin births, the odds of subsequent preterm singleton birth were OR 2.13 (95% CI, 1.21-3.74) if twins were born between 34 and 366 weeks, OR 5.18 (95% CI, 2.78-9.64) if twins were born between 30 and 336 weeks and OR 9.78 (95% CI, 4.99-18.98) if twins were born before 30 weeks gestation. A similar trend was seen for risk of singleton preterm birth after prior spontaneous twin preterm birth. CONCLUSIONS History of preterm twin birth is associated with higher odds of subsequent preterm singleton birth. The odds increase with decreasing gestational age of previous twin birth.