For critical obstetrical judgment, no single laboratory test or biophysical technique has proved completely effective in preventing fetal deaths. Endocrine assessment of high-risk pregnancies has proved helpful in managing pregnancies with diabetes, hypertension, third trimester bleeding, suspected IUGR, and postdate pregnancies. No single endocrine test has proved to be effective in all cases, and much research remains to be done. Of the current endocrine factors being evaluated when all factors are considered, serum unconjugated estriol would appear to be the best predictor of fetal distress or well-being. However, it must be remembered that interpretation of laboratory values is difficult, and that there are many false positives and false negatives. Perhaps the greatest problem with estriol interpretation is short-term and daily fluctuations. If the estriol values are used as the only indicator for following high-risk pregnancies, there is a very likely possibility of delivering a normal premature infant that was wrongly diagnosed as having fetal distress. In the following high-risk pregnancies with estriols, the delivery decision should not be based on a single factor. Rather, the decision to deliver should be based on the estriol values, monitoring of the fetal heart rate (rhythm strip or OCT), amniotic fluid evaluation for fetal lung maturity, and clinical judgment.