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Since antiquity, multiple births have fascinated humanity. Twins, triplets, and higher order births attract public attention and bemusement that often belies appreciation of specific management challenges not associated with singleton pregnancies. In addition, certain complications of pregnancy, such as preterm birth, occur more frequently with higher order gestations. Optimal management requires knowledge of issues associated with multifetal gestation during pregnancy, at delivery, and into the neonatal period.

The incidence of multiple births in developed countries has risen significantly. The increase in twin and higher order multiple births has occurred in conjunction with increases in maternal age and the use of assisted reproductive technologies (ART), ovulation-inducing agents, and artificial insemination. At least a quarter of successful ART procedures result in multiple pregnancies which, in turn, account for 2% to 3% of all live births. Multiple pregnancies are associated with higher risks for both the mothers and the infants. Preterm birth occurs in 50% of twin pregnancies, with 10% taking place before 32 weeks’ gestation. Multiple pregnancies in general, but also as a result of ART, are associated with high direct costs for the medical system of any country as well as for the families. Consequently, many colleges of obstetrics and gynecology and professional bodies associated with ART have endorsed the implementation of a mandatory 2-embryo transfer policy with further consideration of a selective single embryo transfer policy.

The increase in the number of multiple births is recognized as a significant public health concern because of the associated mortality and morbidity risks that will be discussed in this chapter.


Because multiple pregnancies are at higher risk of morbidity and mortality for the infants compared to singleton pregnancies, early assessment is crucial so that appropriate care for these pregnancies can be provided which, in turn, will optimize outcomes. Early ultrasound assessment is crucial for (1) determination of chorionicity, (2) appropriate pregnancy dating, and (3) proper labeling of the fetuses.

Multifetal gestations are classified on the basis of zygosity and chorionicity. Dizygotic twins arise from independent fertilization of separate ova. Monozygotic twins develop from a single fertilized ovum that subsequently divides at or before the blastocyst stage of embryogenesis. The factors promoting fission of the conceptus are poorly understood. The timing of embryonic division determines whether the monozygotic twins will be separated by amnion and chorion (dichorionic, diamniotic), amnion only (monochorionic, diamniotic), or not separated (monoamniotic, monochorionic). Dizygotic twins account for approximately two-thirds of spontaneous twin births and are almost always dichorionic, diamniotic. Monochorionic twins share a single placenta with a shared circulation. Higher order multiples can be a combination of monozygotic and dizygotic gestations. Monozygotic triplets arising from a single fertilized ovum are extremely rare. Monochorionic pregnancies experience more complications and loss compared to dichorionic pregnancies. Determination of chorionicity is critical to determine which pregnancies are at risk and require careful monitoring. ...

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