An extremely rare phenomenon, superfetation, or superfoetation, is the fact that a woman becomes pregnant when she is already pregnant, only a few days apart. Only about ten cases are currently confirmed in the world. Superfluous pregnancy, on the other hand, is more common in animals, especially rodents such as rabbits.

Usually, a woman stops ovulating when she becomes pregnant. Superficiality is the fact of having two ovulations, delayed by a few days. We can therefore observe two fertilizations of the oocytes, which can be the result of two relationships: with the same partner or two different men. 

The two fetuses will implant in the uterus and evolve later. They will therefore have different weights and sizes. The phenomenon is all the more exceptional since the modification of the endometrium, also called the uterine lining, is generally not compatible with the implantation of another egg in the uterus. Indeed, in the days following fertilization, it will thicken with the appearance of blood vessels and cells to provide a favorable environment for implantation.

The case of in vitro fertilization (IVF)

In France, during IVF, doctors implant a maximum of two embryos whose age can vary from D2 to D4 for example. Their term will be postponed by a few days. We can then speak of superfluous pregnancy.

In most cases, a thorough medical examination will explain this exceptional phenomenon. In a study published in 2008 by the Journal of Obstetrics and Reproductive Biology *, scientists put forward several suggestions: 

• A genetic system “qualitatively and / or quantitatively stimulates the placental production of hCG, can trigger another ovulation and allows implantation”; 
• Double ovulation: it sometimes occurs in women on medication to promote procreation; 
• A uterine malformation: such as a didelphic uterus, also called a double uterus, for example.

In the case of superficiality, we cannot speak of twins who are conceived during a single sexual intercourse. Monozygotic twins are produced from the same egg split in two during the first 15 days after fertilization. In the case of dizygotic twins, or “fraternal twins”, we observe the presence of two oocytes having been fertilized by two spermatozoa during the same report.

The rarity of cases and the skepticism of some health professionals vis-à-vis this phenomenon, make pregnancy superfluous difficult to detect. Some will be confused with dizygotic twin pregnancies.  

It is mainly the intrauterine growth retardation of one of the fetuses that makes it possible to suspect a superficiality. It will be important to determine if the difference in height is due to a difference in gestational age or if it is a growth disorder that could be a symptom of an abnormality or health problem in the future. baby.

As in the case of a twin birth, the delivery of the first fetus will trigger that of the second. Infants are delivered at the same time, although one of the babies will be slightly less developed.