First-trimester chorionic gonadotropin measurements as an aid in the diagnosis of early pregnancy disorders

Abstract

In order to evaluate the usefulness of serial human chorionic gonadotropin (hCG) levels as a first-trimester placental function test, we prospectively collected 685 serum samples from 256 women during the first 100 days of gestation. Dating of the samples was based upon the thermal shift in the basal body temperature (BBT). Human chorionic gonadotropin was measured by use of a sensitive and relatively specific radioimmunoassay, and the results were correlated with the outcome of pregnancy. The 90 per cent tolerance limits for normal serum hCG levels were established by measurements made on 489 samples obtained from 187 pregnancies. A pregnancy was judged to be abnormal if two or more serum samples collected at two-week intervals showed hCG levels above or below the 90 per cent tolerance limits 14 or more days after the BBT shift. Using this criterion, 1.6 per cent of normal pregnancies, 57.6 per cent of pregnancies which terminated in a spontaneous first- or second-trimester abortion, 100 per cent of ectopic pregnancies, and 60 per cent of pregnancies complicated by multiple gestations showed abnormal first-trimester serum hCG levels. The predictive value of serial hCG measurements was further demonstrated by a second prospective study in 28 patients for whom the outcome of the pregnancy was predicted based upon the normal range. All of the normal pregnancies were correctly identified, while 88.9 per cent of the pregnancies resulting in spontaneous abortions and all of the ectopic pregnancies were correctly predicted to be abnormal. These results indicate that the majority of patients with ectopic pregnancies or those whose pregnancies are destined to terminate in a first- or second-trimester spontaneous abortion will have abnormally low serum hCG levels. We conclude that serial first-trimester serum hCG determinations are useful for distinguishing between normal and abnormal trophoblastic function.