Sex of prior children and risk of stillbirth in subsequent pregnancies.
BACKGROUND
Delivery of a boy has been reported to increase a woman's risk of recurrent miscarriage in subsequent pregnancies. We explored whether delivery of boys similarly increases the risk of a subsequent stillbirth.


METHODS
We identified all Danish women delivering their first child (singleton) between 1980 and 1998 (n = 499,731) using the Danish Birth Registry. These women had subsequent singleton births through 2004 (n = 558,314). We assessed the risk of stillbirth conditional on sex of prior children.


RESULTS
The risk of stillbirth was increased by 12% after deliver of boys compared with girls (relative risk = 1.12 [95% confidence interval = 1.02-1.23]). This association did not appear to be explained by maternal confounders.


CONCLUSIONS
Stillbirth risk appears to be slightly higher among the pregnancies of women who have previously delivered a boy. One possible mechanism is maternal immune response to male-specific minor histocompatibility antigens initiated during pregnancies with boys.
Nielsen
Henriette Svarre
HS
The National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark. henriette.svarre.nielsen@rh.regionh.dk
Mortensen
Laust H
LH
Nygaard
Ulrikka
U
Schnor
Ole
O
Christiansen
Ole Bjarne
OB
Andersen
Anne-Marie N
AM
D001722:Birth Order; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology / Q000209:etiology; D012042:Registries; D018570:Risk Assessment; D012737:Sex Factors; D035781:Siblings; D050497:Stillbirth / Q000453:epidemiology*