Fetal Gender of the First Born and the Recurrent Risk of Spontaneous Preterm Birth.
OBJECTIVE
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.


METHODS
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).


CONCLUSIONS
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.
Center for Reproductive Medicine, Department of Obstetrics and Gynaecology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands.
Esmé I
EI
Kamphuis
Center for Reproductive Medicine, Department of Obstetrics and Gynaecology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands.
Bouchra
B
Koullali
Department of Clinical Epidemiology, Bioinformatics, and Biostatistics, Academic Medical Centre, Amsterdam, The Netherlands.
Michel
M
Hof
Department of Obstetrics and Gynecology, VU University Medical Centre, Amsterdam, The Netherlands.
Christianne J M
CJ
de Groot
Center for Reproductive Medicine, Department of Obstetrics and Gynaecology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands.
Brenda M
BM
Kazemier
The Robinson Research Institute | School of Paediatrics and Reproductive Health, University of Adelaide, South Australia, Australia.
Sarah
S
Robertson
The Robinson Research Institute | School of Paediatrics and Reproductive Health, University of Adelaide, South Australia, Australia.
Ben W J
BW
Mol
Center for Reproductive Medicine, Department of Obstetrics and Gynaecology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands.
Anita C
AC
Ravelli
D000328:Adult; D001722:Birth Order; D005260:Female; D005865:Gestational Age; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D007234:Infant, Premature; D008297:Male; D009426:Netherlands / Q000453:epidemiology; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology*; D012008:Recurrence; D012042:Registries; D012189:Retrospective Studies; D012307:Risk Factors; D012737:Sex Factors