Comparison of urinary estrogens, contraction stress tests and nonstress tests in the management of postterm pregnancy

In a retrospective review of 697 postterm pregnancies we attempted to validate three tests used to identify the fetus at increased risk: the 24-hour urinary estrogen per gram creatinine (E/Cr), the nonstress test (NST) and the contraction stress test (CST). Using the corrected perinatal mortality rate (PMR) among term pregnancies (0.23%) as a standard for comparison, we found the PMRs among postterm patients with negative screening tests to be as follows: 0.23% with normal E/Crs, 0.65% with negative CSTs (not significantly different) and 2.4% with reactive NSTs (p<0.005). When we used intrapartum fetal distress as a standard for comparison, the E/Cr exhibited the highest sensitivity (88%) whereas those of the CST and NST were much lower (7-10%). The specificities were 63%, 98% and 92%, respectively. From this retrospective study the E/Cr appears to be of most assistance in identifying fetuses at increased risk, the CST is of intermediate assistance, and the NST is of least assistance.