Monozygotic pregnancies conceived by in vitro fertilization: understanding their prognosis.

OBJECTIVE To analyze the outcomes and particular characteristics of monozygotic (MZ) pregnancies conceived by in vitro fertilization (IVF). DESIGN Retrospective data analysis. SETTING Large private-academic fertility center. PATIENT(S) IVF-conceived MZ pregnancies. INTERVENTION(S) Statistical analysis of MZ pregnancy outcomes depending on fetal order and pregnancy reductions status. MAIN OUTCOME MEASURE(S) Spontaneous pregnancy reduction, pregnancy loss, take-home baby rate, perinatal mortality, gestational age at delivery, and birth weight. RESULT(S) A total of 72 of 3,426 pregnancies (2.1%) were MZ, and 70 were included in the study. Of these, 34 cases (48.5%) were high-order multiple pregnancies (HOMP), and 36 (51.5%) were non-HOMP. In the HOMP group, only 2.9% (1 of 34) had a complete pregnancy loss while 38.8% (14 of 36) of the non-HOMP were lost by 20 weeks' gestation. Of the HOMP patients, 73.1% therapeutically reduced the MZ component, and a statistically significant difference in gestational age of delivery (37.8 ± 3.2 vs. 28.1 ± 7.7) and birth weight (2796 ± 865.8 vs. 1110.0 ± 731.6) was seen when compared with nonreduced HOMP. CONCLUSION(S) Twinning with MZ is encountered in a small but important number of pregnancies derived from assisted reproduction. The prognosis for these patients is unfavorable, particularly for single-implantation MZ pregnancies and for nonreduced HOMP. Patients who do not spontaneously reduce a MZ-HOMP by 12 weeks may benefit from therapeutically reducing the MZ component of the pregnancy.