Twins from IVF help each other survive in utero

The live birth rate, per implanted embryo, is higher in twin than in singleton pregnancies resulting from assisted conception (83% vs 76%, respectively) because embryos that might otherwise fail as singletons survive when implanted next to healthy siblings, according to a Spanish study.

The retrospective study analyzed data on 1,159 singleton and 523 dichorionic twin pregnancies and found that the number of double births in twin pregnancies was higher than would have been anticipated if the embryos did not somehow assist each other (72% vs an expected 58%) and that the number of single births was lower than expected (22% vs an expected 36.5%). Observed and anticipated double losses were similar (6.1% observed vs 5.8% expected).

Although the overall miscarriage rate was higher for women aged 34 years and older, the difference in live birth rates between single and twin pregnancies was even more pronounced: It was 2.4-fold higher than in younger women.

Older maternal age accounts for about one-third of the increase in twins, while assisted reproductive technologies (ART) and non-ART treatments account for about two-thirds of the increase.

Miró F, Vidal E, Balasch J. Increased live birth rate in twin pregnancies resulting from embryo assistance. Obstet Gynecol. 2012;119(1):44-49.

Martin JA, Hamilton BE, Osterman MJK. Three decades of twin births in the United States, 1980-2009. NCHS data brief, no 80. Hyattsville, MD: National Center for Health Statistics; 2012.