Amniotic fluid insulin levels and fetal abdominal circumference at time of amniocentesis in pregnancies with diabetes.

AIMS

Fetal hyperinsulinism is a strong predictor for excessive growth and fetopathy in pregnancies complicated by diabetes. We examined (i). the relationship between measurements of amniotic fluid insulin (AF insulin) and fetal abdominal circumference (AC) at the time of amniocentesis, and (ii). whether there is a threshold for fetal AC percentiles which can identify low vs. high-risk levels of AF insulin without performing an amniocentesis.

METHODS

In a retrospective study, AF insulin from 121 pregnant diabetic women (32 pregestational; 89 gestational) was measured during the 3rd trimester as part of a diabetes management protocol. AC measurements were transformed into a continuous variable of percentile growth for gestational age (Hadlock). Division of the cohort according to deciles or quartiles of AC percentiles was performed to identify a threshold AC with a significant increase in elevated AF insulin, previously defined as AF insulin >or= 7 microU/ml. A receiver operator characteristic (ROC) curve was created and the negative predictive value (NPV) of the determined threshold was calculated.

RESULTS

AF insulin levels were significantly correlated with the AC percentiles (r = 0.3, P = 0.0005) by linear regression. No AC threshold could reliably identify a moderate elevated AF insulin >or= 7 microU/ml (NPV 77.2%), but an AC threshold >or= 75th percentile could identify with fetal hyperinsulinism with an AF insulin >or= 16 microU/ml. All 10 cases of AF insulin >or= 16 microU/ml were identified with a NPV of 100% (74/74).

CONCLUSIONS

Our data indicate that an AC >or= 75th percentile determined by a 3rd trimester ultrasound examination may discriminate between pregnancies at low vs. high risk for AF insulin >or= 16 microU/ml. This AF insulin concentration corresponds to a level of hyperinsulinism reported to be associated with considerable neonatal and long term morbidity.