Yes, You Can Get Pregnant When You’re Already Pregnant

Think being pregnant prevents another pregnancy? Surprisingly enough, getting pregnant while you’re already pregnant may seem like a far-fetched notion, but it IS possible. So if you’re asking “Can you get pregnant while pregnant?” the answer is yes. 

Don’t let this fact scare you. The very rare occurrence of getting pregnant during an existing pregnancy is known as “superfetation,” and it happens when someone who is already pregnant becomes pregnant a second time, ultimately giving birth to twins who are a few days or weeks apart in gestation.

Superfetation is extremely rare, and there are a few reported cases in medical literature. Very little is actually known about the condition, how it works, and what causes it to happen.

With this article, we aim to share a bit more about what superfetation is, the biological processes behind it, and potential causes and risks associated with it. We’ll also shine a spotlight on notable, real-life cases of successful superfetation worldwide.

What Is Superfetation? (And How Is It Different from Twins?)

Superfetation is the extremely rare phenomenon of getting pregnant while you are already pregnant. The normal processes of pregnancy (like hormonal changes) stop ovulation so that when an embryo is developing in your uterus another pregnancy can’t take hold. But in very rare cases, the body bypasses those natural barriers to create the conditions for a second pregnancy to develop. 

A superfetation pregnancy is when you get pregnant while you are already pregnant. Even though the pregnancies are similar, it is not a twin pregnancy and they are not the same thing. Twins are two eggs fertilized at the same time, whereas superfetation is two eggs fertilized at different times. In superfetation, a second ovulation and implantation takes place after the initial pregnancy to create a second pregnancy in the same womb and the babies are conceived weeks apart and are of different gestational ages. 

A third combination is known as superfecundation, in which two eggs are fertilized within the same cycle by different sexual encounters. Essentially, multiple eggs are released and fertilized during multiple sexual encounters. Two or more eggs can be fertilized by the same partner or different partners resulting in fraternal twins with different fathers. Twins with different daddies is an extremely rare occurrence and may only be discovered if paternity is contested. With the rise of fertility treatments and drugs to induce ovulation, though, it may occur more often than we realize. 

Why Is Superfetation So Rare?

In typical pregnancies, the following biological barriers are put in place to stop a second pregnancy from developing:

• ovulation stops

• cervix seals with mucus plug

• uterine lining thickens 

Once an egg has been fertilized and implanted in the uterine wall, the body then initiates these processes so that you’re unlikely to get pregnant again. 

After implantation, your body ramps up the production of pregnancy hormones like hCG (human chorionic gonadotropin), estrogen, and progesterone to support a pregnancy. The uterine lining itself thickens to support a growing embryo, but also to tell the body to stop menstruating. This halts all other “normal” processes of a typical menstrual cycle - including ovulation. Meanwhile, your cervical mucus becomes increasingly sticky and thick in order to prevent new sperm, bacteria, or viruses from reaching the uterus. It eventually forms a “mucus plug” and acts as a protective barrier throughout pregnancy. 

Together, these processes make it highly unlikely you will get pregnant again while already pregnant. For superfetation to occur, your body would need to release an additional egg (ovulation), have sperm meet the egg to be fertilized, and implant into the uterine lining to develop. If all three of these events are able to take place in an existing pregnancy, superfetation is possible; however, the chances of all three happening successfully are extremely low. It is so rare that little medical research has been done to study exactly what causes it, the likelihood of it happening, and potential symptoms. 

Understanding your menstrual cycle and your unique cycle patterns can help you plan and optimize your fertility more precisely. Keeping track of the timing of ovulation can help you plan a pregnancy or avoid one as well. There are many methods to track ovulation from calendars and apps to basal body thermometers and monitoring your cervical mucus. 

One of the most accurate ways to predict and confirm ovulation is by tracking your hormones directly. Even if you are not trying to conceive, hormone testing can help you understand other aspects of your reproductive health. This can be done with an at-home hormone tracking device like Mira. With Mira, you can track key hormone levels like estrogen (and its metabolite in urine E3G), LH, progesterone (and its metabolite in urine PdG), and FSH in a simple and non-invasive way. You can get precise daily hormone level readings, similar to those from a lab, and monitor your hormonal map over time through dynamic charts on your smartphone – clearly pinpointing your ovulation patterns. 

How Does Superfetation Happen? (Step-by-Step Process)

Conceiving while pregnant is extremely rare and a number of steps need to take place before it is even possible to happen, let alone likely. 

Step 1: Ovulation During Pregnancy

Pregnancy hormones rise rapidly in the first trimester and are responsible for many of those telltale early signs of pregnancy. After implantation, hCG (human chorionic gonadotropin), estrogen, and progesterone prevent ongoing ovulation. It’s why you don’t have a period while you’re pregnant, but in rare cases ovulation may still take place. 

Step 2: Sperm Fertilizes a Second Egg

The second step necessary for superfetation to occur is fertilization. That means that once an egg is released, it must be fertilized by a sperm. To conceive, sperm must travel through the vagina and cervix in order to reach an egg in the uterine tubes.

After implantation, progesterone levels rise to help support your body in maintaining a pregnancy. It does this through thickening the uterine lining, preventing ovulation, and aiding in the development of the cervical mucus plug. Cervical mucus becomes increasingly sticky and thick to form a “plug” that acts as a protective barrier. It prevents bacteria or viruses from reaching the uterus, but also from sperm entering the uterus to fertilize a new egg. For superfetation to occur, a second sperm must make it through the protective mucus barrier in order to both find and fertilize another egg. 

Step 3: Implantation Against the Odds

Once fertilization happens, the fertilized egg must then not only be able to find a spot in an already occupied uterus, but it must also endure the implantation process. Considering the fact that in typical pregnancies, the body will have stopped producing key hormones that aid with implantation, this process for the second fertilized egg can be extremely difficult.

If all three of these events are able to take place in an existing pregnancy, superfetation is possible. However, the chances of all three happening successfully are extremely low.

Many of the reported cases of superfetation have occurred in those already undergoing certain fertility treatments, such as in-vitro fertilization. For example, it’s possible to ovulate even after a fertilized egg has already been transferred to the uterus via IVF. If the second egg released through ovulation becomes fertilized, then it is possible to become pregnant “again” shortly after an IVF procedure. 

Documented Cases of Superfetation

Surprisingly, superfetation is actually quite common and well-documented in mammals such as panthers, buffalo, and hares. However, it is an extraordinarily rare occurrence among humans due to the biological processes that must take place for it to happen.

There are very few reported cases of superfetation (less than 10 documented in medical research worldwide) – here are three of the most notable cases.

Can You Detect Superfetation Before Birth?

A superfetation pregnancy can be hard to diagnose. Pregnancy symptoms aren’t necessarily unique to the type of pregnancy you have so you may not notice anything out of the ordinary. Early ultrasounds may even miss the second pregnancy because the second baby is smaller than the first and may go unseen. 

Doctors and ultrasound technicians aren’t usually on the lookout for someone getting pregnant while pregnant because it is such a rare occurrence. Early in a superfetation pregnancy, doctors often simply assume that you are having twins. Over time though, they may notice that one fetus is larger in size than the other. This condition is called “twin growth discordance,” and in addition to superfetation, growth discordance can also be caused by intrauterine growth restriction (IUGR), placental insufficiency, or twin-to-twin transfusion syndrome.

IUGR is a common diagnosis for low growth rate and with proper management you can have a favorable outcome. Superfetation can only be diagnosed and confirmed after birth with DNA testing.

Superfetation is extremely rare but not scientifically impossible. If you suspect superfetation has occurred, it’s important to speak to your doctor right away. While they won’t be able to confirm anything until after the birth, it’s essential for proper fetal management and maternal care for the best possible outcome. 

What Are the Risks of Superfetation?

While there are successful reports of superfetation, there are a few risks involved with this type of pregnancy.

For the Baby

The primary risk for this type of pregnancy is that the second fetus will be developmentally behind the first fetus in the womb. This means that at birth, the second fetus risks being born prematurely. A premature birth can increase a child’s likelihood of experiencing complications such as breathing issues, intestinal problems, and developmental delays. 

For the Mother

In addition to the risks associated with the baby, mothers of twins are also at an increased risk of developing preeclampsia, gestational diabetes, and iron deficiency anemia. Prenatal vitamins can help reduce the risk of these pregnancy complications and help promote overall well-being. They provide essential vitamins for both the mother and baby and help support fetal development. Research shows that this helps to reduce the risk of birth defects - such as anencephaly, spina bifida, and congenital heart disease. Mira’s own Prenatal Multi-Vitamin is crafted in-house by our fertility experts and contains the essential nutrients required before, during, and after pregnancy. 

Is It Riskier Than Twin Pregnancies?

There are inherent complications with carrying more than one baby and twin pregnancies can have increased risks for both the mother and baby. The risks of a superfetation pregnancy are similar to those of a normal twin pregnancy, and it is usually managed the same way as other multiple pregnancies.

The biggest risk of a superfetation pregnancy stems from the differing gestational ages of the fetuses, with one baby developing at a different rate than the other due to different conception times.

Final Thoughts: Should You Worry About Superfetation?

Due to lack of research, there is no specific number or range to describe the average pregnant individual’s “chances” of superfetation, but superfetation is an extremely rare phenomenon and there are very few documented cases of it happening. So can you get pregnant while pregnant? Yes. Should you worry about it? No! 

Getting pregnant while pregnant (superfetation) is so rare that your chance of experiencing this phenomenon is nearly zero. Doctors and medical experts tend to agree that the odds of it occurring are “extremely small,” with Good Morning America reporting that the chances of it happening are “one in several million.” One doctor explained that you are more likely to win the lottery or get struck by lightning than have a superfetation pregnancy. 

Frequently Asked Questions

Can you ovulate while pregnant? Can you ovulate during pregnancy? 

It is extremely rare and you are unlikely to ovulate during pregnancy as there are biological processes in place to prevent it, but it is scientifically possible.

How to conceive twins?

There are no guaranteed ways to conceive twins. Multiples are more likely in some situations like with in vitro fertilization (IVF) and some fertility drugs. Your chances of conceiving twins are also higher if you have a family history of multiples.