title: Fetal trisomy 21 and maternal preeclampsia.
abstract: BACKGROUND
  Placental trophoblast shedding into maternal circulation has been hypothesized as a potential cause of preeclampsia. Because pregnancies with a trisomy 21 fetus also have high levels of fetal cells and cell-free fetal DNA in maternal circulation, we examined whether trisomy 21 pregnancies have a higher risk of preeclampsia than euploid pregnancies.
  
  
  METHODS
  We used 2 population-based databases. We identified 7763 pregnancies with a singleton trisomy 21-affected fetus and 15,293 matched euploid gestations from the U.S. Natality files for the period 1995-1999. The second database consisted of 665 pregnancies with fetal trisomy 21 and 987 euploid controls in a population-based Down syndrome study in California. In the latter study, women were interviewed by telephone regarding characteristics and pregnancy complications. Gestational hypertension and preeclampsia are the outcomes of this study.
  
  
  RESULTS
  The U.S. Natality files showed that in nulliparous women fetal trisomy 21 was associated with a reduced risk of pregnancy-induced hypertension (adjusted relative risk [aRR] = 0.67; 95% confidence interval [CI] = 0.53 to 0.85). Findings from the California study confirmed this association in nulliparous women, and further revealed that the decrease in overall risk of pregnancy-induced hypertension was mainly the result of a large reduction in the risk of preeclampsia (aRR = 0.19; CI = 0.04 to 0.88) rather than in gestational hypertension by itself (0.83; 0.37 to 1.84). Neither dataset showed these effects among multiparous pregnancies.
  
  
  CONCLUSIONS
  Fetal trisomy 21 is associated with a reduced, rather than increased, risk of preeclampsia, specifically in nulliparous women.
authors.affiliation: Epidemiology Branch, National Institute of Child Health and Human Development, National Institutes of Health, Department of Health & Human Services, NIH Building 6100, Room 7B03, Bethesda, MD 20892, USA. jim_zhang@nih.gov
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.forename: Roberta E
authors.initials: RE
authors.lastname: Christianson
authors.forename: Claudine P
authors.initials: CP
authors.lastname: Torfs
mesh_terms: D000328:Adult; D002140:California / Q000453:epidemiology; D016208:Databases, Factual; D004314:Down Syndrome / Q000453:epidemiology*; D004522:Educational Status; D005260:Female; D006801:Humans; D006973:Hypertension / Q000453:epidemiology; D007231:Infant, Newborn; D008297:Male; D010298:Parity; D011225:Pre-Eclampsia / Q000453:epidemiology; D011247:Pregnancy; D011249:Pregnancy Complications, Cardiovascular; D011295:Prenatal Care; D012907:Smoking / Q000009:adverse effects; D014481:United States / Q000453:epidemiology