Multiple gestation or multiple pregnancy occurs when two or more fetuses are conceived at the same time in the same woman. It can be differentiated from the term "multiple births" because it refers to the conception of fetuses and may or may not result in live births of multiple babies. In some cases, a woman's body may naturally reduce the number of fetuses present, or a woman may decide to reduce the number due to the health risks associated with multiple gestation.
With multiple gestation, the fetuses are monozygotic or dizygotic. Monozygotic means that, during conception, the sperm fertilizes an egg, which will then divide into two or more developing embryos. These types of siblings are genetically identical and almost always of the same sex.
Dizygotic multiples occur when a woman's body releases multiple eggs, and those eggs are fertilized by different sperm. The resulting fetuses are full siblings and are not identical. Fraternal twins or triplets are generally as similar to each other as other regular siblings.
Several factors can increase the possibility of multiple gestation. There is a higher rate of occurrence with the use of fertility drugs or treatments, such as in vitro fertilization. Multiple gestation is also more likely to occur in older women or those who have a family history of multiple births.
With this type of pregnancy, the mother faces some additional considerations. Usually she has to eat more than if she were pregnant with only one baby. The mother-to-be may also experience more discomfort due to the additional weight gain and also because her uterus becomes larger than that of a typical pregnant woman.
There are additional risks associated with multiple gestation. The mother is more likely to develop hypertension or gestational diabetes, and may experience more nausea and vomiting during pregnancy. During childbirth, there is also a danger of prolonged labor and excessive bleeding. These mothers are also more likely to give birth by cesarean section than by vaginal delivery.
Multiple gestation is also more likely to cause preterm labor, which can lead to even more complications. Babies born prematurely are likely to have a lower birth weight and could have developmental problems or serious health problems. In particular, cerebral palsy is more common among twins, triplets, and other multiples.
A mother carrying two or more fetuses should expect more medical supervision and specialized prenatal care. The mother may need to have more frequent visits with her doctor or have additional tests. Although multiple gestation can be more complicated than single births, most outcomes are positive.