Kamphuis, E.Koullali, B.Hof, M.De Groot, C.Kazemier, B.Robertson, S.Mol, B.Ravelli, A.2018-09-272018-09-272015American Journal of Perinatology, 2015; 32(14):1305-13100735-16311098-8785http://hdl.handle.net/2440/114699Objective: To study, in women with a spontaneous preterm birth (sPTB) in the first pregnancy, the effect of fetal sex in that first pregnancy on the recurrent sPTB risk. Study Design: A nationwide retrospective cohort study (data from National Perinatal Registry) on all women with two sequential singleton pregnancies (1999–2009) with the first delivery ending in sPTB <37 weeks. We used logistic regression analysis to study the association between fetal gender in the first pregnancy and the risk of recurrent sPTB. We repeated the analysis for sPTB < 32 weeks. Results: The overall incidence of sPTB <37 weeks in the first pregnancy was 4.5% (15,351/343,853). Among those 15,351 women, the risk of recurrent sPTB <37 weeks was increased when the first fetus was female compared when that fetus was male (15.8 vs. 15.2%; adjusted odds ratio [aOR] 1.2; 95% confidence interval [CI] 1.05–1.3). A similar effect was seen for sPTB <32weeks (8.2 vs. 5.9%; aOR 4.5; 95% CI 1.5–13). Conclusion: Women who suffer sPTB of a female fetus have an increased risk of recurrent sPTB compared with women who suffer sPTB of a male fetus. This information provides proof for the hypothesis that sPTB is due to an independent maternal and fetal factor.en© 2015 by Thieme Medical PublishersFetal gender - recurrent spontaneous preterm birthJournal article003003708310.1055/s-0035-15637160003662262000042-s2.0-84950325955213544Robertson, S. [0000-0002-9967-0084]Mol, B. [0000-0001-6887-0262] [0000-0001-8337-550X]