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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.

Authors
  • Mortensen, Laust H1
  • Cnattingius, Sven2
  • Gissler, Mika3, 4
  • Klungsøyr, Kari5, 6
  • Skjaerven, Rolv6, 7
  • Nybo Andersen, Anne-Marie1
  • Nielsen, Henriette S8, 9
  • 1 Section of Epidemiology, Department of Public Health, University of Copenhagen, Copenhagen, Denmark. , (Denmark)
  • 2 Division of Clinical Epidemiology, Department of Medicine Solna, Karolinska Institutet, Stockholm, Sweden. , (Sweden)
  • 3 Finnish Institute for Health and Welfare, Helsinki, Finland. , (Finland)
  • 4 Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, Stockholm, Sweden. , (Sweden)
  • 5 Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway. , (Norway)
  • 6 Division for Mental and Physical Health, Norwegian Institute of Public Health, Oslo, Norway. , (Norway)
  • 7 Center for Fertility and Health, Norwegian Institute of Public Health, Oslo, Norway. , (Norway)
  • 8 Department of Obstetric and Gynecology, Hvidovre Hospital, University Hospital Copenhagen, Copenhagen, Denmark. , (Denmark)
  • 9 Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark. , (Denmark)
Type
Published Article
Journal
Acta Obstetricia Et Gynecologica Scandinavica
Publisher
Wiley (Blackwell Publishing)
Publication Date
Oct 01, 2020
Volume
99
Issue
10
Pages
1381–1386
Identifiers
DOI: 10.1111/aogs.13872
PMID: 32304226
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

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. 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. 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%. 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. © 2020 Nordic Federation of Societies of Obstetrics and Gynecology (NFOG). Published by John Wiley & Sons Ltd.

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