Human chorionic gonadotropin rise in normal and vanishing twin pregnancies.

OBJECTIVE: The purpose of the study was to describe and to compare the rate of rise of human chorionic gonadotropin (hCG) in vanishing twin and normally progressing twin pregnancies during the first trimester.

DESIGN: All patients with twin pregnancies between 1985 and 1989 were prospectively studied. Human chorionic gonadotropin was measured one to three times per week between days 12 and 52 after luteinizing hormone (LH) surge or day of hCG administration (day 0). Pelvic ultrasound (US) was performed weekly beginning on day 24.

SETTING: The study was performed at Rush-Presbyterian-St. Luke's Medical Center in an academic private practice setting of the Section of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology.

PATIENTS: Forty patients who conceived after treatment of infertility and who had two gestational sacs on US examination were included in the study after the following criteria were met: (1) both sacs progressed to exhibit a fetal pole and (2) day of LH surge and/or day of hCG administration was known.

MAIN OUTCOME MEASURE: The rate of rise of hCG was slower in vanishing twin pregnancies than in normally progressing twin gestations for the entire time period studied (P less than 0.05).

RESULTS: A vanishing twin occurred in one third of the twin pregnancies. Forty-six percent of these losses occurred after fetal heart activity had been established.

CONCLUSIONS: Vanishing twin phenomenon occurred in a large proportion of twin pregnancies in this infertility population. Fetal heart activity was not a reliable predictor of continuing fetal viability in early twin gestations. Vanishing twin conceptions were characterized by a slower rate of rise of hCG than normally progressing twin pregnancies.