Asessment of fetal gestational age in high-risk pregnancies by amniotic fluid analyses and ultrasound mensuration.

Maturity studies are reported on 204 women with high-risk pregnancies. Estimates of fetal maturity were made prenatally by the use of ultrasonic measurements, the lecithin/sphingomyelin (L/S) ratio, and a gestational index based on amniotic fluid creatinine, urea nitrogen, and cytology. These estimates were compared with the neonatal pediatric estimate of maturity. The gestational score agreed with pediatric maturity to within 14 days in 95 per cent of the cases. Estimates of L/S ratio distinguished between mature and immature infants in 86 per cent of the cases. Ultrasound could estimate gestational age only to within 14 days in 75 per cent of the cases, and the disagreements were greatest where either growth retardation or macrosomia was present. However, ultrasound is more useful in estimating fetal size and abnormalities of growth pattern. An estimate of gestational age by gestational score aids management, particularly where growth retardation is present, enabling a decision about delivery to be made even though the infant is very small and has an immature L/S ratio.