Mortensen LH, Cnattingius S, Gissler M, Klungsøyr K, Skjaerven R, Nybo Andersen AM, Nielsen HS. Sex 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.
Acta Obstet Gynecol Scand 2020;
99:1381-1386. [PMID:
32304226 DOI:
10.1111/aogs.13872]
[Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2019] [Revised: 03/31/2020] [Accepted: 04/11/2020] [Indexed: 01/05/2023]
Abstract
INTRODUCTION
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.
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