Relationship between normal amniotic fluid index and birth weight in term patients presenting for labor

OBJECTIVE: To investigate whether a relationship between birth weight (BW) and amniotic fluid index (AFI) existed for term patients with intact membra nes and, if so, whether it could predict macrosomia and intrauterine growth retardation. STUDY DESIGN: Two hundred thirty-one eligible women at term (37-42 weeks' g estation) had an AFT between 5.0 and 24.0 cin at the time of admission. Dem ographic information was collected, including BW. Statistical comparisons w ere made, with significance set at P <.05. RESULTS: The mean gestational age was 39.5 weeks, and the mean AFT was 11.3 . There were 28 infants with BWs > 4,000 g (macrosomia). The cesarean secti on rate was 16.9%. Macrosomia was associated with a higher cesarean section rate (39.2% vs. 13.8%, P<.002). The mean AFT was higher for those with mac rosomia (13.5 vs. 11.0, P<.001). Patients with an AFI > 15.0 had over twice the incidence of macrosomia (RR 2.72, 1.1-6.6, 32.1% vs. 14.8%, P <.027). The risk was even greater for them with an AFT > 18.0 (RR 6.4, 2.2-18.7, P< .002). A linear relationship was observed between AFT and BW (r(2) .061, P <.0001). BW increased with increasing AFT. No relationship between AFT of 5 -8 and BW < 2,500 g was found. CONCLUSION: Increasing AFT correlates linearly with increasing BW, and macr osomia is associated with an increased incidence of cesarean delivery. AFI > 15 carries over double the risk of birth of a macrosomic infant, while AF T > 18 has a risk of over six times. No association between low normal AFT and a growth-restricted infant was found.