As we discovered in the first article of the series debunking myths, the gestation process is extremely complex and full of peculiar and wonderful situations.
In this second article we are going to demystify another myth about pregnancy, and that is the belief that a woman cannot get pregnant when she is already pregnant, since it IS possible, although very rare.
Today we come to talk about: Superfetation.
What is superfetation?
Superfetation is a very rare phenomenon in which a woman becomes pregnant while already pregnant. This happens when a new egg is fertilized by a sperm in a different menstrual cycle than the first pregnancy. It is very rare since the normal biological process of a pregnant woman inhibits ovulation and the environment of the uterus is prepared to nourish only one developing embryo, which is why it is a process that has been poorly documented since there are not many cases and it is considered a biological anomaly.
In other animals such as horses, fish and some rodents it is more frequent but in humans it is a truly exceptional condition.
Under what conditions does superfetation occur?
- Despite being pregnant, a woman continues to ovulate, which normally does not happen. During pregnancy, hormones usually stop the ovulatory cycle, so a hormonal imbalance is necessary for this to happen, and this imbalance must not be incompatible with the life of the first baby.
- The second embryo implants in the uterus, which is already occupied by the first developing embryo. This is difficult because the body is already adapted to nurturing the first pregnancy.
- Superfetation is considered possible only during the first 3 months of the first pregnancy, when the first baby is still very underdeveloped and there is still room in the uterus for this second pregnancy to be possible.
What is the probability of having superfetation?
The likelihood of having superfetation is extremely low. This phenomenon is very rare in humans and only a few confirmed cases have been documented worldwide. Because it occurs when the normal biological cycle of pregnancy is disrupted (ovulation stops), the chances of it happening are almost negligible.
There are no precise statistics on the exact frequency of superfetation, but it is considered an extremely rare event. It is more common in some animals, but in humans fewer than a dozen cases have been recorded in modern medical literature.
What is the birth of a woman with superfetation like?
The birth of a woman with superfetation can be complicated because the two babies have different gestational ages. This means that one of the fetuses has had more time to develop than the other. Here are some facts about the birth:
- Doctors usually schedule delivery when the most advanced fetus is ready to be born. The younger fetus may be born prematurely if the time difference between conceptions is significant.
- A baby who was conceived later is usually more immature, so may need special care if born early.
- Depending on the development of both fetuses and the health of the mother, delivery can be vaginal or by Caesarean section. The decision will depend on the condition of the babies and the length of time the pregnancy has been prolonged.
- The two babies may be born with a large difference in their development, meaning that the younger one may need intensive neonatal care if he or she has not reached sufficient maturity.
Does superfetation have any additional risks compared to a normal birth?
The risks for the mother are similar to those of a normal multiple birth, and for the baby they are those of a premature birth if the second baby is not yet fully developed.
Is superfetation genetic?
Superfetation is not considered a genetic phenomenon. There is no scientific evidence to suggest that this condition is hereditary or related to genetic factors, and it is rather considered an extremely rare event that occurs due to unusual biological circumstances, such as the continuation of ovulation after a pregnancy has already started, something that does not normally happen.
Since there is no evidence linking it to genetics, it is believed to be an accidental or exceptional event of the body and not something that can be passed down from generation to generation.
Can superfetation occur with different fathers?
Yes, superfetation can occur with different fathers. This happens if a woman has sexual intercourse with two different men at close times but separated by one ovulatory cycle. If one egg is fertilized by one man's sperm and, later, another egg is fertilized by another man's sperm, both embryos can develop at the same time in the uterus, resulting in fetuses with different biological fathers.
This phenomenon is known as heteropaternal superfecundation and, although it is extremely rare, it has been documented in some cases. In these cases, the fetuses would be half-siblings, sharing the same mother but with different fathers.
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