HCG FREEb-SUBUNIT AN EARLY MARKER OF OUTCOME OF IN VITRO FERTILIZATION CLINICAL PREGNANCIES*

Abstract

In the in vitro fertilization (IVF) and embryo transfer (ET) program at Yale, 32% of pregnancies abort by 16 weeks. With the objective of predicting outcome, serum hCG titers were determined in serial samples from 48 women with clinical pregnancy (conception where fetal sac demonstrated by ultrasound). Although the mean hCG levels were lower at 8-14, 15-21, 22-28 and 29-35 days post-ET in the 18 women who eventually aborted, 0.18 (range 0.01-0.49), 1.5 (0.05-4.7), 6.4 (0.68-27), and 15 nmol/L (0.35-59), respectively, than in the 30 women whose pregnancy went to term, 0.48 (0.01-5.5), 2.2 (0.33-20), 10 (0.46-25), and 116 nmol/L (0.76-335) respectively, the ranges overlapped significantly, limiting the use of serum hCG in prediction. In earlier studies, the free beta-subunit of hCG was demonstrated in the serum of women with natural fertilization pregnancy, 2-6 weeks post ovulation. We used the RIA with 1E5 free beta-subunit monoclonal antibody to measure this component in the IVF serial blood samples. Of the 30 women who had pregnancies that went to term, samples from 28 were positive for this marker by 28 days post-ET (0.02-3.0 nmol/L). In 18 women who aborted, however, only 1 had a detectable serum hCG free beta-subunit level by 28 days post-ET. We conclude that a detectable serum hCG free beta-subunit level by 28 days post-ET may indicate normal term pregnancy outcome.