The most common cause of multiple pregnancies these days is assisted reproductive technology (ART). Treatments that stimulate ovulation can lead to the maturation of several oocytes in a single cycle, and if several embryos are transferred to the uterus during an IVF procedure to increase the chances of success, they can all take! Triplets and even quadruplets can come naturally, but it is much rarer.
How can a multiple pregnancy happen without IVF?
In the case of identical twins, a single embryo divides into two, and each one begins to develop on its own.
Fraternal twins are born when a woman has two or three eggs that mature simultaneously and all fertilize.
Triplets, quadruplets, and quintuplets are most often the product of a combination of two factors: the fertilization of two eggs and the division of one or both.
How often does this happen in nature?
Generally speaking, humans are designed to bear one child at a time. But there can be glitches in the program!
Twins come along quite often; there is one set of twins for every 250 pregnancies.
Triplets occur at a rate of 1 in every 10,000 pregnancies.
Quadruplets are much rarer, with a rate of 1 in every 700,000 pregnancies [1].
But if fertility treatments or IVF are involved, the probability of twins is almost 30% higher, with triplets appearing once in every 1,000 pregnancies [2].
In the United States, the number of embryos implanted in a woman through IVF will depend on her age and prognosis [4].
Does the number of babies affect the course of a pregnancy?
Additional risks are inherent in a multiple pregnancy. The more babies, the harder it is to carry a pregnancy to term. While a single child is carried an average of 38-40 weeks, twin pregnancies average 35, triplets 32, and quadruplets 30 weeks [1]. It is worth noting that many of the known methods of preserving and prolonging a pregnancy prove to be unsuccessful in the case of a multiple pregnancy [3].
Lower birth weight is also common in a multiple pregnancy. Twins tend to weigh around five pounds (2300 g) each at birth, triplets less than four (around 1600 g), and quads can weigh in at three pounds or under (1300 g.) [1].
Future mothers of triplets and quadruplets need to visit their doctor more often than other pregnant women and be in constant contact with them to keep things well monitored and under control.
