Multiple Gestation As the majority of ART cycles involve the transfer of more than one embryo, multiple gestation occurs at higher rates than the 3% rate for spontaneous conception. This has social, medical, emotional, and financial ramifications (379,380). Although the majority of complications of multiple gestations occur with high-order (three or more) multiples, twins have increased risks for low birth weight, preterm birth, and neurologic deficits when compared to singletons (380,390). Despite this, 20% of infertile patients view multiple pregnancy as a desired outcome. Because most patients lack insurance coverage for IVF, patients may push their physicians to take greater risks when deciding on the number of embryos to transfer (379). The multiple pregnancy risk is higher in patients under the age of 35 who are undergoing IVF because their embryos are typically of better quality and implantation rates are higher, but multiple pregnancy can occur at any reproductive age (371). From 1998 to 2007, the overall twinning rate in ART cycles remained stable at 29% to 32%, but the rate of high-order multiples decreased from 6% to 2%. In 2007, the live birth rates for twins and triplets or more for women under the age of 35 who underwent ART in the United States were 33.2% and 3.5%, respectively. Women aged 43 or 44 had twinning live birth rates of 10.6% and triplet or more live birth rates of 0.8% (380). Most multiple pregnancies arising from ART are dizygotic, but monozygotic twinning occurs in 3.2% of IVF cycles (compared to a background rate of 0.4%) (379). Concerns have been raised that monozygotic twinning might increase after blastocyst culture, but this finding has not been consistent (364,369). With increasing adherence to guidelines suggesting limitations on the number of embryos to transfer in a given ART cycle (discussed in “Process of Assisted Reproductive Technologies”) and improved implantation rates that allow single embryo transfer, the multiple pregnancy rates associated with ART should continue to decrease.
Selective Reduction Ten percent of multifetal pregnancies spontaneously lose at least one gestational sac during the first trimester. This loss rate increases to 21% in women older than 35 years of age. The spontaneous reduction rate to twins or singletons is much higher for triplets (14%) than for quadruplets (3.5%) (391,392). Selective pregnancy termination or multifetal reduction may be an option for some patients in whom spontaneous reduction does not occur by 11 to 13 weeks. This involves first karyotyping each fetus through transabdominal chorionic villous sampling to preferentially reduce those that are abnormal, then injecting potassium chloride into the heart of the targeted fetus. Although selective reduction carries a 3% to 7% risk of losing the entire pregnancy when performed prior to 19 weeks, this is still lower than the 15% chance of spontaneously losing an entire triplet pregnancy (390,393). Selective fetal reduction is typically considered for triplet or higher pregnancies, but even reduction from twins to singletons may have benefit (390).
Ectopic and Heterotopic Up to 3.4% of ART pregnancies are ectopic (implantation outside the uterus) and require