'Vanishing Twin' in IVF Pregnancies Tied To Low Birth Weight in Remaining Twin


INDIAN WELLS, CALIF. — Women who conceive through in vitro fertilization and have a “vanishing twin” are still at risk of having the remaining twin born at a low birth weight for gestational age, Mohamed Mitwally, M.D., said at the annual meeting of the Pacific Coast Reproductive Society.

In a review of 945 live-birth deliveries of infants conceived through in vitro fertilization (IVF), 40 patients experienced spontaneous reduction of fetuses in a multiple gestation and then gave birth to one infant.

Those infants weighed a mean 2,842 g at a mean 271 days' gestation. That compared with a mean birth weight of 3,206 g in 514 women who gave birth to singletons and had not experienced fetal reduction, either spontaneous or selective, and a mean birth weight of 3,166 g in 15 patients who delivered singleton infants after selective fetal reductions.

The finding was somewhat unexpected; the main purpose of the study was to investigate if selective fetal reduction really improved birth weight and risk of preterm delivery, said Dr. Mitwally of the division of reproductive endocrinology and infertility at Wayne State University, Detroit.

The study showed that selective fetal reduction did result in better birth weight and less risk of preterm birth, without increased pregnancy loss, except perhaps when twins were reduced to singletons. The reason the study observed no benefit from selectively reducing twins may have been that there were only a few cases in which twins were reduced, Dr. Mitwally said.

The rest of the literature on fetal reduction, including a recent metaanalysis, “supports the findings of this study,” said Sae Sohn, M.D., a fertility specialist who practices in Greenbrae, Calif., and who commented on the study at the meeting.

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