Open AccessSex of the first‐born and obstetric complications in the subsequent birth. A study of 2.3 million second births from Denmark, Finland, Norway, and Sweden
Author(s) -
Mortensen Laust H.,
Cnattingius Sven,
Gissler Mika,
Klungsøyr Kari,
Skjærven Rolv,
Nybo Andersen AnneMarie,
Nielsen Henriette S.
Publication year - 2020
Publication title -
acta obstetricia et gynecologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.401
H-Index - 102
eISSN - 1600-0412
pISSN - 0001-6349
DOI - 10.1111/aogs.13872
Subject(s) - medicine , placental abruption , obstetrics , preeclampsia , relative risk , eclampsia , pregnancy , population , pediatrics , gynecology , fetus , confidence interval , genetics , environmental health , biology
Studies have shown associations between a first‐born boy and increased risks of pregnancy loss, stillbirth, decreased birthweight, and preterm birth in subsequent pregnancies, but with limited precision. Material and Methods We examined associations between sex of the first‐born and obstetric complications in second births. We calculated the relative risks (RR)s of preeclampsia/eclampsia, placental abruption, stillbirth, and preterm birth in approximately 2.3 million second births comparing women with a preceding first‐born boy to those with a first‐born girl using the Medical Birth Registries of Denmark, Finland, Norway, and Sweden 1980‐2008. Results In second births following a first‐born boy rather than a girl, the RR was 4% higher for preeclampsia/eclampsia (RR = 1.04, 95% CI 1.02‐1.06), 9% higher for placental abruption (RR = 1.09, 95% CI 1.05‐1.13), 9% higher for stillbirth (RR = 1.09, 95% CI 1.04‐1.14), and 8% higher for preterm birth (RR = 1.08, 95% CI 1.07‐1.09). The population attributable risks ranged from 2% to 4.5%. Conclusions Male sex of the first‐born is associated with small increases in risks of obstetric complications in the second birth. Exploration of the underlying mechanisms is needed to increase our knowledge and treatment options for these serious obstetric complications.