A multiple pregnancy is any pregnancy in which more than one fetus is present in the uterus. This becomes multiple birth when the babies are born and if at least two survive birth. In human populations, the multiple pregnancy is relatively uncommon when there are no interventions like fertility treatment. About 10% of natural pregnancies are twin births, but higher order multiples occur less frequently. From a maternal-child health perspective, this most supports survival of mother and children. With the advent of fertility medicine, multiple pregnancy numbers have risen, creating demand to treat the special problems such pregnancies pose.
Twins, triplets and even quadruplets do occur naturally, but multiple pregnancy with greater numbers usually results from implantation of a high number of embryos. When high numbers of embryo are implanted, the result can be high numbers of fetuses present in the womb. Generally the more babies, the more likely problems occur.
As the demands on the uterus are higher, babies are usually born at a lower gestational age. A mom of octuplets, an exceptionally rare circumstance, might not make it to the 30th week of pregnancy, and twins are born on average about two to four weeks early. This means lower birth weight, which hazards risks for respiratory distress and cerebral palsy. A higher number of birth defects are also often seen in babies from a multiple pregnancy.
Unquestionably, a multiple pregnancy is riskier to the mother. She stands a higher chance of developing gestational diabetes or eclampsia. She may need to scale back on activities earlier and use bedrest as a means of delaying labor. Twins may be delivered vaginally, but higher order multiples usually require caesarian section. More risk to the health of the uterus also occurs, and there is greater likelihood of conditions like prolapse or hemorrhage.
Given the additional risks of the multiple pregnancy, mothers pregnant with twins or more are usually considered high risk. They require additional prenatal visits to assess the health of the babies and mother. Doctors will advise on acceptable activities, calorie consumption, and in other areas to try to best treat moms.
Some doctors do advise reducing a multiple pregnancy in a procedure called selective reduction. One or more of the fetuses could be aborted to better insure health and safety of the others. For some, this procedure is morally abhorrent, and for all it can pose risk of losing all children during the procedure. Doctors in support of it feel that reduction, though it poses some risk to all fetuses, also greatly increases chances of good maternal and fetal health, for the remaining fetuses.
Another approach, since many are opposed to after the fact reduction methods, is to limit embryo implantation. Reproductive specialists recommend implanting no more than three embryos in any one cycle, and some regions make it illegal to implant more than two. Even if both attach, a twin birth is much less complicated than triplet or quadruplet births. Each additional fetus increases risk of complications.