Indirect prediction of fetal lung maturity. Value of ultrasonographic colonic and placental grading.

Objective: To correlate fetal morphometrics with studies of fetal lung maturity.
Study Design: One hundred six patients undergoing amniocentesis for fetal lung maturity studies were examined prospectively. Eighty-four patients were normal (79%), and 22 were diabetic (21%). Fetal morphometrics were obtained prior to amniocentesis. The fetal colon and placenta were graded. Discriminant analysis was used to identify variables that were predictive of a mature lecithin/sphingomyelin ratio and the presence of phosphatidylglycerol (PG). All patients delivered within 48 hours of amniocentesis.
Results: In the normal group, 28 (33%) fetuses had a grade 3 colon, which was 68% sensitive and 98% specific for a mature amniocentesis. A grade 3 colon was the single best predictor of a mature amniocentesis (P < .001). Twenty-five (29%) fetuses had a grade 3 placenta, which was 64% sensitive and 96% specific for a mature amniocentesis (P < .005). Diabetes did not influence colonic grading since a grade 3 colon was present in seven (32%) patients (47% sensitivity and 100% specificity for PG) (P < .02). Interexaminer and intraexaminer variability for the study was excellent, kappa = 1.0 (P < .001).
Conclusion: Colonic and placental stage 3 grading are reliable and reproducible ultrasonographic scales that can help predict the findings of fetal lung maturity studies.