Early β-human chorionic gonadotropin trends in vanishing twin pregnancies.

To describe the early β-hCG trends in vanishing twins compared with normally progressing singleton and twin pregnancies.Retrospective cohort study.University-based infertility clinic.Women undergoing fresh IVF/intracytoplasmic sperm injection (ICSI) cycles between 1998 and 2010.Early β-hCG level increase in vanished twin pregnancies was compared with the level increase in normally progressing singleton and twin pregnancies.Two-day percent increase in β-hCG level.Pregnancies with vanishing twins demonstrated a significantly lower mean 2-day percent increase in β-hCG level than singletons and twins (114.3% vs. 128.8% and 125.4%, respectively). Vanishing twins arresting at earlier developmental stages demonstrated significantly further reduced β-hCG level increases. Infrequently, all groups had β-hCG level increases less than previously established clinical thresholds that led to a live birth.Early β-hCG level increases are slower in vanishing twins than in singleton and twin pregnancies, with the slowest increases seen when the spontaneous fetal losses occur at earlier developmental stages. All increases, however, are within clinically accepted normal limits. Therefore, abnormal β-hCG level increases should not be attributed to a vanishing twin. Of note, an abnormal β-hCG level trend--even an initial decrease--does not preclude live birth, even in a singleton pregnancy.