title: An amniotic fluid index < or =5 cm within 7 days of delivery in the third trimester is not associated with decreasing umbilical arterial pH and base excess.
abstract: OBJECTIVE
  To determine if an amniotic fluid index (AFI) < or =5.0 cm within 7 days of delivery in the third trimester is associated with decreasing umbilical arterial pH and base excess.
  
  
  METHODS
  Cases for this retrospective cohort study were all pregnancies > or =26 weeks with intact membranes and an AFI < or =5.0 cm within 7 days of delivery between 11/99 and 7/02. Multiple gestations, aneuploid, and anomalous fetuses were excluded. Controls with an AFI >5.0 cm within 7 days of delivery were matched to each case within 1 week by gestational age. For a control group with a mean+/-SD umbilical arterial pH of 7.26+/-0.07 and alpha=0.05, a sample size of 100 would have a power of 99% to detect a difference with a study group whose mean was 7.20. Data were compared using paired Student's t-test, Mann-Whitney, Fisher's exact, chi(2) and risk ratios with 95% confidence intervals.
  
  
  RESULTS
  In all, 131 neonates with an AFI < or =5.0 cm were matched to 131 controls with an AFI >5 cm. There was no difference in gestational age (37.6+/-3.0, 37.7+/-3.0 weeks) or birth weight (2897+/-810, 2762+/-788 g). There was no difference in umbilical artery pH (7.25+/-0.07, 7.26+/-0.07) or base excess (-3.32+/-2.59, -2.83+/-2.45 mmol/l), even in small for gestational age (SGA) infants in both groups. There was no difference in the number of SGA neonates, 5-minute Apgar <7, respiratory distress syndrome, necrotizing enterocolitis, or neurologic morbidity. Linear regression showed no correlation between AFI and either umbilical arterial pH (r=-0.00047, SE=0.001, p=0.63) or base excess (r=-0.029, SE=0.037, p=0.428).
  
  
  CONCLUSIONS
  An AFI < or =5.0 cm measured within 7 days of delivery in the third trimester is not associated with decreasing umbilical arterial pH and base excess.
authors.affiliation: Division of Maternal-Fetal Medicine, Department of Gyn-Ob, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA.
authors.forename: Rita W
authors.initials: RW
authors.lastname: Driggers
authors.forename: Cynthia J
authors.initials: CJ
authors.lastname: Holcroft
authors.forename: Karin J
authors.initials: KJ
authors.lastname: Blakemore
authors.forename: Ernest M
authors.initials: EM
authors.lastname: Graham
mesh_terms: D000137:Acid-Base Imbalance / Q000209:etiology*; D000328:Adult; D001724:Birth Weight; D005260:Female; D005865:Gestational Age; D006801:Humans; D006863:Hydrogen-Ion Concentration; D016104:Oligohydramnios / Q000150:complications*; D010927:Placental Insufficiency / Q000175:diagnosis; D011247:Pregnancy; D011256:Pregnancy Outcome; D011263:Pregnancy Trimester, Third; D012189:Retrospective Studies; D014469:Umbilical Arteries / Q000737:chemistry*