This is the story of a pregnancy, that of Sophie Small. During the first ultrasound at 7 weeks of pregnancy, doctors found two embryos, and a significant difference in size between the two. It was during birth in 2021, that they realized that the two babies are not the same gestational age, reports the British newspaper The Sun, in an article on May 21. The two children were actually conceived 28 days apart. Sophie Small was already pregnant when she became pregnant a second time. Her first baby was born at 36 weeks, while the second, the result of later sexual intercourse, was born younger, at 32 weeks.
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There is an explanation for this extraordinary phenomenon. This is a so-called superfetal pregnancy, which characterizes a pregnant woman a second time during her pregnancy. The latter is considered twin since children are born on the same day, even if they were conceived after two different sexual intercourse. How is that possible? In this case, ovulation continues while it is interrupted during a classic pregnancy. "An egg is therefore expelled by the ovaries while another has already been fertilized during the previous menstrual cycle," explains Olivier Pape, obstetrician gynecologist, author of a thesis on superfetation in 2008. The second is then fertilized in turn through another sexual intercourse, and a second embryo begins to develop." The parents of babies may thus be different.
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A superfetatory pregnancy can only be diagnosed before childbirth under two conditions. First, the various ultrasounds must be able to prove that a second baby appeared later. Then, the growth lag must be constant until birth.
If superfetal pregnancy is a common phenomenon in some animals, it is the exception in the human species. "Only a dozen cases have been studied scientifically to date in the world," says obstetrician gynecologist Odile Bagot.
Medically induced superfetations?
Based on current knowledge, medically assisted reproduction (ART) may be the cause of some cases of superfoetation. "In these specific situations, women continued to ovulate after becoming pregnant thanks to medications prescribed to promote fertilization," says Dr. Odile Bagot.
This is the case of Rebecca Roberts, a British mother who continues to share her testimony on her social networks since the birth of her twins in 2020. After a pregnancy favored by a drug boosting her ovulation, the young woman notes during her third ultrasound the appearance of a second baby. "My twins were conceived three weeks apart. Their size difference was impressive, even during the first weeks after birth," she said in a video posted on YouTube. Her children would be the 14th case of superfetation studied by science, she writes.
Other cases have been observed after in vitro fertilization: "Some patients studied in these cases of superfoetation were inseminated when they had already become pregnant naturally," reports gynecologist Odile Bagot.
A malformation of the uterus?
A genetic predisposition may also exist. "The interruption of ovulation in pregnant women is caused by the production by the placenta of the hormone hCG," explains Dr. Olivier Pape. And the genetic makeup of some women could be the cause of less secretion of this hormone."
In two cases studied, malformations of the uterus were the cause of a superfetal pregnancy. The uterus was then positioned and oriented to promote a second fertilization. "These cases were observed in patients with uteruses called "bicornes" or "didelphes", that is to say having an unusual shape and a smaller size than average," informs gynecologist Olivier Pape.
That being said, gynecologist Odile Bagot wants to reassure: "These pregnancies are so rare that they should not be a cause for concern. It is therefore useless to protect yourself after becoming pregnant, to try to avoid a possible multiple pregnancy. "
