Standardization of amniotic fluid leptin levels and utility in maternal overweight and fetal undergrowth.

Objective: Leptin is an adipokine that regulates energy homeostasis. The objective of this study was to establish a gestational age-specific standard for amniotic fluid leptin (AFL) levels and examine the relationship between AFL, maternal overweight and fetal growth restriction.

Study Design: Amniotic fluid was obtained at mid-gestation from singleton gravidas, and leptin was quantified using enzyme-linked immunosorbent assay. Amniotic fluid samples from 321 term pregnancies were analyzed. Clinical data, including fetal ultrasound measurements and maternal and infant characteristics, were available for a subset of patients (n=45).

Results: The median interquartile range AFL level was significantly higher at 14 weeks' gestation (2133 pg ml(-1) (1703 to 4347)) than after 33 weeks' gestation (519 pg ml(-1) (380 to 761), P trend<0.0001), an average difference of 102 pg ml(-1) per week. AFL levels were positively correlated with maternal pre-pregnancy body mass index (BMI) (r=0.36, P=0.03) adjusting for gestational age at measurement, but were not associated with fetal growth.

Conclusions: AFL levels are higher at mid-gestation than at late gestation, and are associated with maternal pre-pregnancy BMI.