Fueled largely by infertility therapy, over the past 25 years, both the rate and the number of twin and higher-order multifetal births have increased in the United States at an unprecedented pace. Between 1980 and 2005, the twinning rate rose from 18.9 to 32.1 per 1000 live births (Martin and colleagues, 2009). Over the same time period, the number of live births from twin deliveries rose nearly 50 percent, and the number of higher-order multifetal births increased more than 400 percent (Fig. 39-1). However, as discussed later, changing infertility therapy has led to slight decreases in rates of higher-order multifetal births.

Figure 39-1
Graphic Jump LocationGraphic Jump Location

Number of twin (A) and triplet or higher-order multifetal births (B) in the United States, 1980-2005. (From Martin and colleagues, 1999, 2007.)


This extraordinary increase in multifetal births is a public health concern. The higher rate of preterm delivery of these neonates compromises their survival chances and increases their risk of lifelong disability. More than a fourth of very-low-birthweight (<1500 g) neonates born in the United States are the product of a multifetal gestation, as is one in every seven infants who die (Martin and colleagues, 2006; Mathews and MacDorman, 2006). Data comparing singleton and twin outcomes at Parkland Hospital are found in Table 39-1. Comparing twins with triplets or quadruplets, Luke and Brown (2008) found lower risks with twins for preterm prematurely ruptured membranes, preterm delivery, and perinatal mortality.

Table Graphic Jump Location
Table 39-1. Selected Outcomes in Singleton and Twin Pregnancies Delivered at Parkland Hospital from 2002 through 2006 

Multifetal gestations are at higher risk of fetal malformations, and also twin-twin transfusion syndrome may develop. Maternal complications are also increased. Walker and colleagues (2004) studied more than 44,000 multifetal gestations and found that, compared with singletons, risks for preeclampsia, postpartum hemorrhage, and maternal death were increased twofold or more. Wen and co-workers (2004) reported that these maternal risks correlated with fetal number. Francois and associates (2005) reported that compared with women who delivered singletons, those who delivered twins were three times as likely to undergo emergent peripartum hysterectomy, and those who delivered triplets or quadruplets were 24 times as likely. Maternal risks of multifetal gestation are not exclusively acute or physical. Choi and associates (2009) reported that at 9 months postpartum, mothers of multifetal births were almost 50 percent more likely to have moderate to severe depressive symptoms than mothers of singletons.


Twin fetuses usually result ...

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