Fetal gender and gestational-age-related incidence of pre-eclampsia.

Background: Male fetal gender is associated with an overall increased risk of pre-eclampsia. However, it was recently shown that the male: female birth ratio was decreased in pre-eclampsia associated with preterm delivery. The reason for this discrepancy is not known.

Objective: To investigate whether the fetal and newborn gender is associated with the incidence of antenatal maternal pregnancy complications, and to investigate if gender-associated risk changes with gestational age at delivery.

Methods: Population-based study including 1,158,276 infants born in Sweden 1990-2001. Five maternal diagnosis groups (pre-eclampsia, infection, preterm premature rupture of membranes, abruptio placentae, and polyhydramnios) were explored in relation to newborn infant gender and gestational age at delivery.

Results: When all gestational ages were evaluated, male newborn gender was associated with increased odds ratios for all five diagnosis groups, and for preterm birth before 37 weeks gestation, M/F ratio 1.17. In very preterm births (gestational age below 32 weeks), male newborn gender was associated with a significantly lower risk for pre-eclampsia (OR 0.88, 95%CI 0.80-0.97), and a marginally lower risk for polyhydramnios (OR 0.74, 95%CI 0.54-1.01).

Conclusion: The fetal gender seems to affect the occurrence of pre-eclampsia, and possibly also polyhydramnios. The finding could be due to an increased risk for spontaneous abortions in pregnancies with male fetuses, but could also be associated with the etiology of these conditions. Evaluation of antenatal pregnancy complications from a fetal/newborn gender perspective may contribute to new insights regarding their pathophysiological mechanisms.