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Multifetal pregnancies may result from two or more fertilization events, from a single fertilization followed by an “erroneous” splitting of the zygote, or from a combination of both. Such pregnancies are associated with increased risk for both mother and child, and this risk increases with the number of offspring. For example, 60 percent of twins, 90 percent of triplets, and virtually all of quadruplets are born preterm (Martin, 2012). From these observations, it is apparent that women were not intended to concurrently bear more than one offspring. And although they are often viewed as a novelty or miracle, multifetal pregnancies represent a potentially perilous journey for the mother and her unborn children.

Fueled largely by infertility therapy, both the rate and the number of twin and higher-order multifetal births have increased dramatically since 1980. Specifically, the twinning rate rose 76 percent from 18.9 to 32.1 per 1000 live births in 2009 (Martin, 2012). During the same time, the number of higher-order multifetal births increased more than 400 percent to a peak in 1998. Since then, however, evolving infertility management has resulted in decreased rates of higher-order multifetal births to its lowest level in 15 years. Specifically, the rate of triplets or more decreased by 10 percent from 153 per 100,000 births in 2009 to 138 per 100,000 births in 2010 (Martin, 2012).

The overall increase in prevalence of multifetal births is of concern because the corresponding increase in the rate of preterm birth compromises neonatal survival and increases the risk of lifelong disability. For example, in this country, about a fourth of very-low-birthweight neonates—those born weighing < 2500 g—are from multifetal gestations, and 15 percent of infants who die in the first year after birth are from multifetal pregnancies (Martin, 2012). In 2009, the infant mortality rate for multiple births was five times the rate for singletons (Mathews, 2013). A comparison of singleton and twin outcomes from infants delivered at Parkland Hospital is shown in Table 45-1. These risks are magnified further with triplets or quadruplets. In addition to these adverse outcomes, the risks for congenital malformations are increased with multifetal gestation. Importantly, this increased risk is for each fetus and is not simply because there are more fetuses per pregnancy.

TABLE 45-1Selected Outcomes in Singleton and Twin Pregnancies Delivered at Parkland Hospital from 2002 through 2012

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