In the United States, pregnancies associated with assisted reproductive technology (ART) or ovulation-inducing drugs are more likely to result in multiple births than spontaneously conceived pregnancies (1). In addition, triplet and higher-order multiple births are at greater risk than singleton births to be preterm (< or = 37 completed weeks' gestation), low birthweight (LBW) (i.e., < or = 2500 g), or very low birthweight (i.e.,