Amniotic fluid insulin levels in nondiabetic pregnant women: an update

Elevated amniotic fluid insulin levels in diabetes are frequently described but there are few systematic data on metabolically healthy women to define normal ranges. Previous studies had too high normal ranges because they were based on unspecific insulin binding radioimmunoassays. The aim of the study was to update normal amniotic fluid insulin data and to define a reliable normal range in the course of a nondiabetic pregnancy. Amniotic fluid insulin levels were measured in 841 amniotic fluid samples of 707 nondiabetic women undergoing amniocentesis for hydramnios, suspected malformation, determination of lung maturation, Rhesus antibodies and cordocentesis. Mean (+/- SD) of amniotic fluid insulin level was 3.6 (+/- 2.1) microU/mL at 31.5 (+/- 4.9) weeks of pregnancy. The 97th percentile was 8.2 microU/mL. Insulin levels show a biphasic course between 16th and 42nd weeks of pregnancy with a zenith at 30th week. Only two cases (0.3%) had unexplicably elevated amniotic fluid insulin levels > or = 10 microU/mL. Thus, in nondiabetic women amniotic fluid insulin levels > 10 microU/mL are unlikely.