We all know that fertility varies from woman to woman: Fertility can even vary from one pregnancy to the next. Some women may struggle for ages to conceive or need to rely on medications and treatments to get pregnant. Other women may seem to be very fertile and have no problem getting pregnant as soon as they begin trying. And of course, accidents can happen and others may be caught off guard with a surprise pregnancy. The unthinkable can also occur…getting pregnant while already pregnant. It may seem impossible, and may even seem to go against nature and what we’ve been told about our bodies, but for a small number of women – it has actually happened!
This crazy phenomenon can happen two ways. One way is known as superfetation, where a pregnant woman releases an egg, despite already being pregnant. That second egg gets fertilized, and then the woman is pregnant with two babies simultaneously.
This is not to be confused with superfecundation – which is when two eggs get released during the same cycle, but get fertilized at different times.This means that it’s actually possible for a woman to be pregnant with two babies at the same time – and that she can even be impregnated by different fathers! Of course, this goes against everything we know about female biology.
Pregnancy hormones are supposed to shut down a woman’s reproductive system and make it impossible to ovulate when she is pregnant. However, sometimes it happens… and a woman becomes pregnant while she’s already pregnant!
14 Yup... It's Possible!
You already know how a baby is made. Egg + sperm = baby. One of the “perks” to being pregnant is not having to worry about a menstrual cycle for nine months. No menstrual cycle, no ovulation, right?
Well, in an unusual phenomenon known as superfetation, a pregnant woman releases ANOTHER egg a few weeks into her pregnancy. If that second egg becomes fertilized, the woman is then pregnant with two babies simultaneously.
A woman technically should not be able to ovulate if she’s pregnant. There’s not a lot of medical data available to explain how superfetation manages to happen even when it is not supposed to.Some may point out that these cases of twins or double births could just be the result of the slower growth and development of one of the twins. It’s possible. However, reproductive medicine expert Karen Boyle points out that we can’t just dismiss the possibility of superfetation just because it’s not always recognized when it does happen.
13 Delayed Implantation
In humans, superfetation seems to happen so rarely that Boyle was only able to find ten cases of it on record when she appeared on Good Morning America to discuss the topic.Boyle suggests that superfetation occurs when the implantation of the first embryo is delayed, which prevents the initial spike in pregnancy hormones. Delayed implantation of an embryo happens in rabbits, horses, sheep, kangaroos, and rodents. Some of these animals actually have two uteri to accommodate the double pregnancy, or their menstrual cycle continues despite the pregnancy. In humans, superfetation seems to happen so rarely that Boyle was only able to find ten cases of it on record when she appeared on Good Morning America to discuss the topic.
After her segment aired on Good Morning America, Boyle received many comments and messages from people who believed that they experienced superfetation themselves. Many others wrote to say that they knew of sets of twins, one of whom appeared to have been conceived much later than the other.
12 Against The Odds
Although it can happen in animals, it seems like superfetation in humans is a very rare accident. Normally, when a woman is pregnant, the hormonal and physical changes of pregnancy work together to prevent another conception. In the case of superfetation, somehow, a pregnant woman still continues to ovulate. But there are still a few other roadblocks that egg will need to get past before getting fertilized!
After ovulation, the egg needs to come in contact with a male’s sperm. Considering the tricky timing involved in trying to conceive, this isn’t an easy task. Not only that – if a woman is already pregnant, then somehow the male’s sperm has to bypass the mucus plug that will block the cervix.
If, despite all these factors, the egg still manages to get fertilized, implantation still needs to happen. When a woman is already pregnant, her hormones may make the uterus an unfavorable place for another fertilized egg to implant.
11 The Timing Has To Be Just Right
There is only a handful of days during a woman’s menstrual cycle when pregnancy is possible. There are technically six days in the “fertile window” of a woman’s cycle, made up of the typical lifespan of sperm, which is 5 days, and the lifespan of an egg, which is only about 24 hours.
If a woman only has sex six or more days before she ovulates, the chances that she’ll get pregnant are about zero. If she has sex five days before ovulation, her chances bump up to about 10%. If a woman has sex three days leading up to and including the day she ovulates, she has a much better chance of becoming pregnant.
Timing is everything when it comes to conceiving. We already know it doesn’t always happen on the first try. So the chances of successfully conceiving not once, but on two separate occasions, during a fertile window is obviously very rare.
10 The Egg Needs To Get Fertilized
So the timing somehow manages to work out… not once, but twice. A woman conceives and gets pregnant, and then somehow, despite already being pregnant, her body releases another egg. To get that egg fertilized, the chances are, again, really slim to begin with. For the majority of a menstrual cycle, women’s bodies are rejecting sperm. Sperm die within a few hours because they can’t survive in the acidic pH level in the vagina.
These chances are made seemingly even more impossible due to the current pregnancy. During pregnancy, a mucus plug forms in the opening of the cervix. The mucus plug acts as a barrier to keep disease-transmitting bacteria from entering the pregnant uterus. In addition to keeping bacteria out, it basically keeps sperm out of the uterus, too, which means that those little swimmers won’t make it anywhere near the fallopian tubes, which is where fertilization takes place.
9 The Fertilized Egg Needs To Implant
If a pregnant woman ovulates again, and that egg somehow manages to become fertilized, for superfetation to occur, that egg will need to successfully implant in the uterus. Implantation typically happens seven to ten days after ovulation and it can only happen in a specific uterine environment. Obviously, the best conditions needed for implantation to occur would call for a woman who is not already pregnant. That uterus gets crowded pretty quickly!
Researchers have been studying why some embryos successfully implant in the womb and lead to pregnancy, and why other embryos fail. It is believed that human embryos produce a chemical which signals to the uterus that it’s time to prepare its lining for implantation. With that line of thinking, there must be some biological mistake or accident for a second fertilized egg to implant in an already-pregnant uterus. Or, depending on how you look at it, the conditions must be exactly, perfectly, right.
8 Are The Babies Born At the Same Time?
In many of the earlier known cases of superfetation, the babies’ age difference wasn’t discovered until after both children were delivered. The babies were born at the same time, although technically, one was really born a few weeks prematurely.
It is thought that there is a possibility some cases of superfetation may have gone undocumented. It was likely thought that the difference in birth size and weight of the two babies was due to one baby’s growth and development simply being retarded in the uterus, rather than being conceived weeks after the first baby was conceived. Because the second baby would be delivered prematurely, there is a possibility of complications.
Nowadays, it’s possible that the superfetation can be spotted via an ultrasound, which gives the parents and the medical team time to plan for multiple deliveries. Usually, the babies are delivered via a planned C-section, since they will reach full-term at different times.
7 Risks Of Superfetation
The most obvious risk of superfetation would be delivering a baby prematurely. Superfetation babies are born at the same time, meaning that depending on the length of time between the two conceptions, there’s a risk that a normally timed birth for one baby will be a premature birth for the other.
A baby is considered premature if he arrives before 37 weeks. While not all premature babies have health problems, the earlier in a pregnancy a baby is born, the more likely he is to have concerns. Premature babies may need to stay in the hospital longer after birth, and may also have long-term health issues that can stay with them their whole lives. Some premature babies may have issues with jaundice, anemia, infections, and problems with their heart, lungs, immune system, and other systems of the body.
A premature baby may need special equipment, treatment, or medicine in the hospital, and even after he goes home.
6 Wouldn't It Just Be Like Having Twins?
No, although the mother is carrying two babies, superfetation is not the same thing as having twins. Multiple births, such as twins and triplets, are on the rise, due in part to the increased use of fertility treatments. There are a few different ways that a woman can become pregnant with twins.
Multiple eggs are released. Both (or more eggs) are fertilized. This is how fraternal twins are conceived. This can happen with or without the use of fertility drugs.One egg is released, but splits in two, resulting in identical twins. This can also happen with or without the use of fertility drugs.In the case of IVF, there may be more than one fertilized egg put back into the uterus. The thought behind replacing more than one fertilized egg is that they may not all implant; however, they sometimes do.
Unlike having twins, which occurs when multiple eggs are fertilized at the same time or a fertilized egg splits in two, superfetation leads to a woman being pregnant with a second baby that’s younger than the pre-existing pregnancy. In the few cases of superfetation that have been studied, the age gap between the two babies is usually no greater than a few weeks.
5 And Then There's Superfecundation!
While we’re on the topic of twins, let’s talk about superfecundation. (Superfecundation is not the same as superfetation.) Superfecundation refers to when a woman releases multiple eggs during ovulation. This of course, results in twins, like we mentioned before.
As you may know from brushing up on biology while trying to conceive, there’s a window of time during ovulation that the egg is released and can be successfully fertilized. When we think of twins, we assume that the egg or eggs they came from were fertilized during a single act of intercourse. However, it’s actually possible for one egg to be fertilized during one attempt, and the other egg during another attempt. A couple could have sex in the morning and later on in the evening and conceive twins, one egg in the morning, and one at night.
That ovulation window can last a few days, and with more than one egg released, if a woman has sex more than once during that window – or with more than one man – there’s a chance that the multiple released eggs could be fertilized at different times…
…by different men. That’s called heteropaternal superfecundation. Try and wrap your head around that for a minute!
4 Two Babies Conceived Two Weeks Apart
Julia Grovenburg, an Arkansas woman, became pregnant twice, two weeks apart. Her babies had separate due dates: her daughter Jillian was due on December 24, and her son Hudson was due on January 10.
Due to the difference in the size of the two developing babies, Grovenburg's obstetrician, Dr. Michel Muylaert, confirmed during the pregnancy that the couple was likely dealing with a case of superfetation. When Grovenburg went in for her ultrasound, they initially saw one baby developing. That baby was of a certain gestational age. They then noticed another heartbeat in a baby that was much younger developmentally.
A 2009 TIME magazine article documented Grovenburg’s story, which baffled readers, doctors, and researchers alike. However, the article went on to say that the situation shouldn’t cause much concern. It was thought that the pregnancy would behave like a twin pregnancy. Because the age difference between the babies was only two weeks, the second baby would be nearly full-term anyway. Grovernburg gave birth to two healthy babies on December 2, 2009.
3 Two Babies Conceived Ten Days Apart
In 2015, a woman in Australia thought she might never become pregnant, but she gave birth to twins who were conceived ten days apart, despite only having sex once during her fertile period. How in the world is s that even possible?
As a result of superfetation, Kate Hill conceived twin daughters, Charlotte and Olivia, ten days apart. The girls were born on the same day, but had different due dates. They were also born at different sizes, weights, and stages of development. It was also reported that the twins have different blood types.
What makes the situation even more unusual is that Hill and her husband only had sex that one time. That means that his sperm stayed alive for ten days and hung around long enough to fertilize the second egg that was released.
Hill was receiving hormone treatmenst for PCOS, polycystic ovary syndrome, a condition that meant she was not ovulating regularly.
2 A Possible Cause?
While it’s still hard to understand how superfetation can happen, one possible explanation points to fertility treatments. Kate Hill from Australia was undergoing hormonal therapy due to her PCOS, and she and her husband conceived two babies ten days apart. It’s thought that PCOS can cause complications with ovulation, making it very difficult for women suffering with the condition to conceive. While it has been suggested that hormonal medications and fertility treatments might change the functions of the body enough to allow a woman with PCOS to finally be able to get pregnant, it’s still unclear how superfetation manages to occur.
Because of Hill’s reproductive assistance, her doctor was able to determine exactly when she got pregnant. Because embryos develop at a rapid pace, especially in the early stages of pregnancy, it was easy to track the growth of both babies and see that they were in different stages of development.
Even though it may seem highly impossible for Hill to have gotten pregnant twice within ten days, it happened. Some things can’t be explained, not even by science.
1 Don't Freak Out
To date, there are less than a dozen cases of superfetation on record. Due to the small number of recorded double pregnancies that researchers have to work with, it's still not clear why superfetation sometimes occurs. There is no telling whether there are any factors that can increase the likelihood of superfetation, but it is definitely an extremely rare situation - one that you probably don't have to worry about!