title: Reproductive factors and extreme levels of maternal serum alpha-fetoprotein: a population-based study.
abstract: BACKGROUND
  Levels of maternal alpha-fetoprotein (AFP) are increased during multiple gestations and preeclampsia but little is known regarding AFP levels in relation to other reproductive factors. Consequently, the objective of this work was to describe the possible relationship between AFP levels during pregnancy and maternal age at birth, maternal age at first birth, parity, time since previous birth and gender of the offspring.
  
  
  METHODS
  Based on national registries we obtained the reproductive history on a population-based cohort of 44 227 women who had serum AFP levels determined in gestational weeks 14-21 and whose present and previous pregnancies resulted in live-born singletons.
  
  
  RESULTS
  Many previous births and an interval of less than 2 years since last birth were significantly associated with extremely low levels of AFP in the mother. However, age at first birth and age at present pregnancy did not influence the AFP level. Women who gave birth to a girl had AFP levels that were 5%[95% confidence interval (CI) 4-6%] lower than those of women who had a boy. Adjustment for birthweight did not significantly affect the estimate.
  
  
  CONCLUSIONS
  Low serum AFP levels in pregnancy are significantly correlated with high parity and with a short interval between births. The significantly lower levels of AFP in women who gave birth to girls could indicate a possible gender-specific regulatory mechanism.
authors.affiliation: Department of Epidemiology Research, Danish Epidemiology Science Center, Statens Serum Institut, Copenhagen, Denmark.
authors.forename: Ulrikke
authors.initials: U
authors.lastname: Lei
authors.forename: Jan
authors.initials: J
authors.lastname: Wohlfahrt
authors.forename: Peter
authors.initials: P
authors.lastname: Christens
authors.forename: Tine
authors.initials: T
authors.lastname: Westergaard
authors.forename: Mats
authors.initials: M
authors.lastname: Lambe
authors.forename: Bent
authors.initials: B
authors.lastname: Nørgaard-Pedersen
authors.forename: Mads
authors.initials: M
authors.lastname: Melbye
mesh_terms: D000293:Adolescent; D000328:Adult; D015415:Biomarkers / Q000097:blood; D015331:Cohort Studies; D003718:Denmark; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008423:Maternal Age; D010298:Parity; D011159:Population Surveillance; D011247:Pregnancy / Q000097:blood*; D011256:Pregnancy Outcome; D011261:Pregnancy Trimester, First / Q000097:blood; D011262:Pregnancy Trimester, Second / Q000097:blood; D012042:Registries; D012737:Sex Factors; D013997:Time Factors; D000509:alpha-Fetoproteins / Q000032:analysis*
chemical_list: D015415:Biomarkers; D000509:alpha-Fetoproteins