Increase in ambient temperature may explain decrease in amniotic fluid index.

Abstract

In the third trimester, the amniotic fluid index (AFI) may be affected by maternal fluid status. As the ambient temperature increases, there is an increase in insensible fluid loss and the potential for dehydration. We hypothesize that as temperature increases there would be a concomitant decrease in AFI. From June 11 to August 16, 1993, during a period of unusual high heat, 42 women with singleton pregnancies between 27 and 40 weeks' gestation undergoing serial antenatal testing had AFI determinations recorded at least weekly. The daily high ambient temperature in our urban area was subsequently obtained. A 2-, 3-, and 4-day mean temperature prior to the test date was compared to AFI using a Spearman-rank Correlation. The daily high temperature ranged from 71 to 104 degrees F and AFI values ranged from 1.7 to 24.7 cm during the study period. There was a significant correlation between the 2-, 3-, and 4-day mean temperature and AFI, with the 4-day mean being the most significant (r = 0.31, p < 0.001). Fluctuations in ambient temperature are inversely correlated to changes in AFI. This relationship should be taken into account when interpreting the AFI as a measure of fetal well-being.