Amniotic fluid tests for fetal maturity in normal and abnormal pregnancies

Area of Science:

• Obstetrics and Gynecology
• Perinatal Medicine
• Neonatal Physiology

Background:

• Accurate assessment of gestational age and fetal maturity is crucial for optimal pregnancy management.
• Various biochemical and biophysical parameters in amniotic fluid have been explored to estimate fetal maturity.
• Complications such as diabetes, hypertensive disorders, and intrauterine growth retardation can impact fetal development and maturity.

Purpose of the Study:

• To evaluate the accuracy of amniotic fluid creatinine, lipid-positive cells, and L/S ratio in estimating gestational age (EPG) across normal and abnormal pregnancy states.
• To assess the reliability of these parameters, particularly the L/S ratio, in predicting fetal pulmonary maturity near term.
• To identify potential discrepancies and limitations of these tests in specific pathological pregnancies.

Main Methods:

• Analysis of amniotic fluid samples from 285 normal pregnancies and 222 abnormal pregnancies (Rh isoimmunization, diabetes, hypertensive disorders, intrauterine growth retardation, hydramnios).
• Determination of amniotic fluid creatinine levels, percentage of lipid-positive cells, and L/S ratio.
• Calculation of the coefficient of correlation between true gestational age and estimated period of gestation (EPG) derived from the tested parameters.

Main Results:

• High correlation (0.94) between EPG and true gestational age in normal pregnancies.
• Lower correlation coefficients observed in abnormal pregnancies: Rh isoimmunization (0.77), diabetes (0.67), and hypertensive disorders (0.59).
• In intrauterine growth retardation, depressed L/S ratio and creatinine led to consistently underestimated EPG (0.61 correlation). Mean L/S ratios were depressed in pre-eclampsia and diabetes.
• L/S ratios accurately assessed pulmonary maturity in 150 samples near delivery, with a 20% incidence of false-immature results overall, and no false-mature results except in two diabetic cases.

Conclusions:

• Amniotic fluid parameters provide a reliable estimation of gestational age and fetal pulmonary maturity in normal pregnancies.
• The accuracy of these tests is reduced in pregnancies complicated by diabetes, hypertensive disorders, and intrauterine growth retardation.
• The L/S ratio is a valuable tool for assessing fetal lung maturity, though caution is advised due to potential false-immature readings, particularly in diabetic pregnancies.