Impact of obstetric history on the risk of spontaneous preterm birth in singleton and multiple pregnancies: a systematic review.

BACKGROUND: Information about the recurrence of spontaneous preterm birth in subsequent twin/singleton pregnancies is scattered. OBJECTIVES: To quantify the risk of recurrence of spontaneous preterm birth in different subtypes of subsequent pregnancies. SEARCH STRATEGY: An electronic literature search in OVID MEDLINE and EMBASE, complemented by PubMed, to find recent studies. SELECTION CRITERIA: Studies comparing the risk of spontaneous preterm birth after a previous preterm and previous term pregnancy. DATA COLLECTION AND ANALYSIS: The absolute risk of recurrence with a 95% confidence interval and the absolute risk of preterm birth after a term delivery were calculated. Data from studies were pooled using the Mantel-Haenszel method. MAIN RESULTS: We detected 13 relevant studies. The risk of recurrence of preterm birth was significantly increased in all preterm pregnancy subtypes, compared with their term counterparts. Women pregnant with twins after a previous preterm singleton had the highest absolute risk of recurrence (57.0%, 95% CI 51.9-61.9%), and after a previous term singleton their absolute risk was 25% (95% CI 24.3-26.5%). Women pregnant with a singleton after a previous preterm twin pregnancy have an absolute recurrence risk of 10% (95% CI 8.2-12.3%), whereas a singleton pregnancy after delivering a previous twin up to term yields a low absolute risk of only 1.3% (95% CI 0.8-2.2). Women pregnant with a singleton after a previous preterm singleton have an absolute recurrence risk of 20% (95% CI 19.9-20.6). AUTHOR'S CONCLUSIONS: The risk of recurrence of preterm birth is influenced by the singleton/twin order in both pregnancies, and varies between 10% for a singleton after previous preterm twins to 57% for twins after a previous preterm singleton.