Serum level of ${eta}$ subunit of human chorionic gonadotropin (${eta}-hCG$) was studied to evaluate its predictability of pregnancy outcome in 98 in vitro fertilization and embryo transfer(IVF-ET) patients using gonadotropin-releasing hormone(GnRH) agonist. Serial serum ${eta}-hCG$ levels were established for 42 singleton pregnancies, 20 normal multiple pregnancies, 18 preclinical abortions, 14 clinical abortions and 4 ectopic pregnancies. In comparison to normal singleton pregnancies, multiple pregnancies showed significantly higher ${eta}-hCG$ levels on the post-ET day 10 to 13 and day 24 to 25. Clinical abortions did not show significantly lower ${eta}-hCG$ levels in early pregnancy except the post-ET day 16-17, but showed significantly lower ${eta}-hCG$ levels from the post-ET day 22, compared with singleton pregnancies. Preclinical abortions showed significantly lower ${eta}-hCG$ levels than those of singleton pregnancies. Ectopic pregnancies showed lower ${eta}-hCG$ levels than those of singleton pregnancies without statistical significance. In conclusion, determination of serum ${eta}-hCG$ level in early pregnancy is a useful tool for the prediction of preclinical abortions and multiple pregnancies and serial measurement of serum ${eta}-hCG$ levels will be helpful in predicting clinical abortion.