Why are there so many multiple pregnancies with In Vitro Fertilization? 2026

In recent years, the number of twin babies has increased significantly, a circumstance resulting from current assisted reproduction techniques. Medicine has always known the spontaneous incidence of multiple pregnancies: one double or twin pregnancy for every 84 single pregnancies, that is, one pair of twins are born for every 84 single children.

During the first years of In Vitro Fertilization, as pointed out by Dr. Juan Ordás, specialist in Gynecology and Reproductive Medicine at the Assisted Reproduction Unit of the Vithas Nuestra Señora de América Hospital, there was a very high incidence of multiple pregnancies.

Amazon Essentials by Sofia Grainge - Summer 2026 Promotion

"Although, under normal health conditions, a mother tolerates a twin pregnancy quite well, despite the fact that there is greater morbidity and mortality than in a single pregnancy, it is not the same in the event that there are three or more fetuses in the mother's womb." In this case, as the specialist points out, "the very high rates of abortion, premature births, maternal hemorrhages and serious pathologies associated with pregnancy make pregnancy completely undesirable in these circumstances."

The law on assisted human reproduction techniques limits the maximum number of embryos that can be transferred in each cycle to three. Even so, although rare, a small number of triple pregnancies can occur which, as Dr. Ordás states, “we must avoid.”

Twin pregnancy in figures

Of the percentage of children born after an In Vitro Fertilization cycle, between 20 and 22% correspond to pregnancies with two fetuses, rarely three. As Dr. Ordás points out, “if we limit the transfer of embryos to only two, the figures are reduced to less than 18%, but we are still well above the one in 84 that occurs naturally.”

The usual complication of twin pregnancy is prematurity: "children born with low weight have to remain in pediatric intensive care units and have higher mortality and morbidity. To this must be added the concern about the future development of these children, often burdened by growth disorders, diseases and defects in intellectual development."

The current trend in Reproductive Medicine is aimed at preventing pregnancies from occurring, no longer triples, but doubles. To achieve this, as Dr. Ordás points out, a series of changes are being tested based on the better quality of the embryos and the better preparation of the mother's endometrium. "The transfer of single, good quality embryos on day +5 of their development provides a higher number of pregnancies if we compare it with the transfer on day +3. However, we do not always do it this way because the methods for selecting the best embryos are still imprecise and not all of them reach development on day +5; sometimes none arrive, therefore, and while we perfect the techniques, the current policy must continue."