If a woman is pregnant, is it possible for her to get pregnant again? This question definitely seems impossible, but, incredible as it may seem, it is a situation that can happen. Only one in every 1 million pregnancies will occur this way and this extremely rare condition is called superfetation.

What Is Superfetation?

Superfetation is when an additional fetus is conceived days or even weeks after the first baby has been created. A baby conceived through superfetation will usually be born on the same date as the first baby, because this is medically necessary. In most cases, there is induction of labor or a c-section, but, gestationally, one baby is “older” than the other. Superfetation is much more common among animals; among mammals, it is well documented in dogs, rabbits, kangaroos, sheep, buffalo, horses, and panthers, but it is “almost” nonexistent in humans — which still, however, puts us in the statistics. Difference Between Regular Twins and Superfetation (h2) Superfetation differs from the conception of twins, where multiple eggs are released in a single cycle. This can happen naturally or be stimulated with fertility drugs. When more than one egg is fertilized and implants in the uterus, the result is dizygotic twins, triplets, or other multiples. In superfetation, however, they differ in maturity, as they were conceived days or even weeks apart.

Is Superfetation a Rare Condition?

To call superfetation in humans “rare” would be underestimating how unusual this phenomenon is. Up until now, science has been able to confirm about eleven cases since 1932, the year of the first report. Some cases of pregnancy with these characteristics stand out because of the difference in age between the babies. Still, experts have doubts about some of these cases documented in the medical literature. On the other hand, these same experts admit that it is not known with exact certainty how often superfetation occurs (if it actually does), because being so uncommon, a case of superfetation may go undetected and not be properly reported, being mistaken for regular twin pregnancies.

Difference in Size and Weight of the Babies

The difference in gestational age and size can, in some cases, be attributed to a medical condition such as twin-to-twin transfusion syndrome, a condition in which two babies share the same placenta (most twins have separate placentas) due to abnormal formation of important blood vessel connections, and one of the twins absorbs a greater share of nutrients.

Children with Different Fathers

This results in one baby being larger than the other, although in these cases they are always identical twins, while in cases of superfetation the babies will not be identical, and can even have different fathers. This size difference is called growth discordance. Growth discordance is not uncommon, and as noted above, it can be caused by twin-to-twin transfusion syndrome. Other possible causes of growth discordance include congenital infection and chromosomal abnormalities. In the case of fraternal twins, it can literally come down to “luck,” as genetically some babies are programmed to be larger or smaller at birth than others.

How Does Superfetation Happen?

Some scientists are still skeptical about superfetation and believe there must be another explanation for cases where it seems to have happened. Normally, physical and hormonal changes occur after conception which make further conception impossible when a pregnancy is already underway. First and most importantly, once a woman is pregnant, ovulation stops. After conception occurs in a normal pregnancy, the corpus luteum (and later the baby’s placenta) releases hormones that stop ovulation. In addition, the lining of the uterus thickens to prevent a second embryo from attaching. Finally, the cervix forms a barrier known as the mucous plug, which is designed to protect the developing fetus from microbes that could enter the uterus from outside.

Improbable Factors

Just as it prevents microbial infection, the mucous plug is also an effective barrier to sperm. To sum up what’s been said before: superfetation is so improbable because three almost impossible things need to happen for it to occur:

  • Ovulation must happen while the woman is already pregnant.
  • Sperm must somehow overcome the mucous plug.
  • Implantation must occur in a uterus that is no longer prepared for it.

Furthermore, there is no medical data available on how superfetation actually happens, since all we have are suppositions. However, one medical theory is that in some cases, it is possible that the implantation of the first embryo is delayed. As a result, the early rise in pregnancy hormone levels is delayed, allowing space for another conception to occur.

Risks of Superfetation

If the two fetuses are at different gestational ages, there is a risk that the second will be delivered prematurely. Since there is a higher rate of twins born before 37 weeks, this increases the risk for the younger baby, leading to serious problems such as undeveloped lungs causing several breathing issues throughout their life. However, most of the verified cases were babies who were only 10 days to three weeks apart, and in these same cases all the babies were generally born safely and without any health problems.

What Causes Superfetation?

Artificial fertility treatments are considered responsible for the cases in which superfetation is believed to have occurred. Although it’s not exactly known how these treatments might influence or even cause this phenomenon.

Most Well-Known Cases of Superfetation

All cases of superfetation are strange, but some have been even more surprising. As mentioned earlier, it is believed that the number of cases has increased because of the growing number of assisted reproduction procedures performed each year. However, we have records of similar cases going back decades, and it is even claimed that there are records in Greek mythology. Here are some cases of superfetation, or at least the best-known ones that have been reported in the medical world: 1. Two babies were born five minutes apart, but the second was conceived when the mother was already two months pregnant

  • In 1960, there was a case of superfetation that was clearly about getting pregnant while already being pregnant. A woman gave birth to two babies whom the nurse thought were twins.
  • However, one of the doctors present at the birth noticed that the baby born five minutes before the other showed all the signs of being premature. To confirm this, the doctor did some tests and took an X-ray of the thigh bones of both boys.
  • The reports revealed that there was a striking difference in the bone age of the two boys, which shouldn’t have been the case if they were twins born at the same time.
  • The doctor realized that the baby born five minutes later was in fact full-term, while the baby born five minutes earlier was premature and had been born two months before the due date. The premature baby was actually conceived when the mother was already two months pregnant with her first baby.

2. Two babies born three weeks apart in Essex

  • In 2007, again in Essex in the United Kingdom, a mother gave birth to two babies who were also conceived three weeks apart. The mother got pregnant again when she was already three weeks pregnant with her first baby.

3. Two babies born on the same day by c-section in Arkansas:

  • In 2009, in Arkansas, a woman conceived another baby while already two and a half weeks pregnant.
  • Once doctors ran the necessary tests, they confirmed that if both babies could reach full term, they would be born nearly a month apart.
  • Both babies were born healthy by c-section on December 2, with one baby being 15 days more premature than the other.

And in Brazil, Has There Been Any Case? At the beginning of the year (2017) a video of an ultrasound scan made the rounds on social media. In the footage, which received thousands of views and shares, the doctor claims it is a case of superfetation, in which the patient had a twin pregnancy and, three weeks later, became pregnant again. According to him, it is possible to see the three embryos: two with the same gestational age and one at a different age. Although it appears to be a possible resident of Barreiras, Bahia, the woman’s identity was not revealed. There is also no information on the doctor who handled the case. Although there are many remarkable things that happen inside a woman’s body while she is pregnant, superfetation is one of the rarest and most surprising of all! See Also: Twin Pregnancy – What Changes to Expect in the Pregnant Woman’s Body? Photos: MultipleParent, Nevit Dilmen