title: Skewed fetal gender distribution in prolonged pregnancy: a fallacy with consequences.
abstract: OBJECTIVE
  Skewed gender distribution and falsely assigned gestational age lead to unnecessary or late obstetric intervention in prolonged pregnancy. The aim of this study was to examine the consequences of a fetal gender-dependent systematic 1.5-day dating error at ultrasound fetometry.
  
  
  METHODS
  A total of 82 484 singleton deliveries >/=37 weeks at 11 hospitals in southern Sweden from 1995 to 2000 were included. Frequencies of labor induction and Apgar scores <7 at 5 min were compared with regard to fetal gender, both before and after correction of gestational age by adding 0.75 days to female-fetus pregnancies and subtracting 0.75 days from male-fetus pregnancies.
  
  
  RESULTS
  The uncorrected odds ratio for having a male baby at >/=42 weeks was 1.41 (95% confidence interval, 1.33-1.49). After adjusting gestational age by +/-0.75 days, the odds ratio reduced to 0.90 (95% confidence interval, 0.84-0.95). The risk for labor induction was significantly above unity in male-fetus pregnancies delivered after 41 weeks when gestational age was corrected for fetal gender, while the risk for female fetuses having a low Apgar score was not significantly increased compared to male fetuses (P = 0.087).
  
  
  CONCLUSIONS
  Skewed gender distribution in prolonged pregnancy results in a higher rate of labor induction in pregnancies with male fetuses at >/=41 weeks, and the risk for newborn females having a low Apgar score in prolonged pregnancy is not significantly increased compared to boys.
authors.affiliation: Perinatal Revision South Registry, University Hospital of Malmö, Sweden. margareta.kitlinski@telia.com
authors.forename: M
authors.initials: M
authors.lastname: Kitlinski Laczna
authors.forename: K
authors.initials: K
authors.lastname: Källén
authors.forename: K
authors.initials: K
authors.lastname: Marsál
authors.forename: P
authors.initials: P
authors.lastname: Olofsson
mesh_terms: D003951:Diagnostic Errors; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007751:Labor, Induced; D008297:Male; D016017:Odds Ratio; D011247:Pregnancy; D011273:Pregnancy, Prolonged / Q000502:physiology*; D012307:Risk Factors; D012744:Sex Ratio