© Shutterstock

What is superfetation? -

Superfetation occurs when a pregnant woman gets pregnant for a second time.

© Shutterstock

What is superfetation? -

With superfetation, a new pregnancy occurs, despite the human body making it nearly impossible to do so.

© Shutterstock

Is it the same as twins? -

No, superfetation pregnancies are not the same as twins, although they share some similarities, such as sharing the same womb and being delivered at the same time.

© Shutterstock

Is it the same as twins? -

The embryos will, however, have different gestational ages, with the first one maturing at a different rate than the second.

© Shutterstock

Is it the same as twins? -

And unlike twins, embryos from superfetation are not formed during the same menstrual cycle.

© Shutterstock

Is superfetation the same as superfecundation? -

No. In superfecundation, two or more eggs are released during the same menstrual cycle. Those eggs are then fertilized, but it does not occur in different menstrual cycles.

© Shutterstock

How common is it? -

Superfetation in humans is extremely rare. So much so that there are only about 10 documented cases.

© Shutterstock

How common is it? -

Superfetation is, however, more common in other species, such as rodents, as well as other small mammals and fish.

© Shutterstock

What happens in superfetation? -

For superfetation to occur naturally, a woman would have to go through two menstrual cycles, consecutively, and each cycle would result in a pregnancy. Then, a few other things would have to happen.

© Shutterstock

What happens in superfetation: ovulation -

First, an egg must be released during an ongoing pregnancy.

© Shutterstock

What happens in superfetation: fertilization -

Then, the said egg must be fertilized. After, it has to implant into the pregnant woman’s womb.

© Shutterstock

How far apart is the embryos’ gestational age? -

In most cases, the gestational age difference between the two embryos is between two and four weeks.

© Shutterstock

It’s very unlikely -

Women’s bodies have very effective mechanisms that prevent this from happening, so bypassing the body’s natural defenses is indeed a rare event. Let’s take a look at some of the ways the body avoids superfetation.

© Shutterstock

Ovulation -

Hormonal changes during pregnancy will prevent ovulation. Without an egg, there’s no pregnancy.

© Shutterstock

The cervix -

The mucus in the cervix thickens during pregnancy, and this makes it extremely difficult for sperm to reach the uterus, making fertilization nearly impossible.

© Shutterstock

Hormones -

Hormone changes not only stop ovulation, but also make it very difficult for an embryo to implant in the uterine lining.

© Shutterstock

Causes -

What exactly causes superfetation remains unknown. The cases are so rare that scientists don't have enough samples to study it. Most of them, however, involve assistive reproductive technologies.

© Shutterstock

Cases: in vitro fertilization (IVF) -

One documented case of superfetation involved a woman who became pregnant with twins through IVF. A third embryo was then discovered. It had been conceived at a different time, without IVF.

© Shutterstock

Cases: artificial insemination -

Another case is that of a woman who became pregnant after undergoing intrauterine insemination (IUI). Doctors discovered that she was already pregnant when she was inseminated. This was, however, an ectopic pregnancy.

© Shutterstock

Cases: surrogate -

Six months after being impregnated with a couple’s embryo through IVF, a surrogate discovered she was carrying a second embryo.

© Shutterstock

Are there any symptoms? -

There are no symptoms specific to superfetation, other than the common ones experienced during a regular pregnancy.

© Shutterstock

Diagnosis -

Diagnosis may prove difficult, especially due to its similarity with other conditions involving twins.

© Shutterstock

Diagnosis -

The only evidence would be one fetus being more developed than the other, indicating a different gestational age.

© Shutterstock

Can superfetation be a misdiagnosis of other conditions? -

Some researchers have suggested this to be the case. One of these conditions is twin-to-twin transfusion syndrome.

© Shutterstock

Twin-to-twin transfusion syndrome -

This is when one twin gets more nutrients through blood, and therefore develops at a faster rate than the other twin.

© Shutterstock

Other conditions -

Placental insufficiency may also lead to a misdiagnosis of superfetation. This occurs when the placenta doesn’t deliver enough nutrients to both fetuses (twins), leading to differentiations in their respective developments.

© Shutterstock

What to do in the case of superfetation? -

A C-section is usually recommended in such cases. This is because both fetuses develop at different rates, and the younger fetus may be born prematurely as a result.

© Shutterstock

Complications of superfetation -

In addition to the risk of premature birth, pregnant women experiencing this condition also face higher risks of complications.

© Shutterstock

Complications of superfetation -

These include gestational diabetes, high blood pressure, and preeclampsia (protein in the urine).

© Shutterstock

Prevention -

The likelihood of a superfetation pregnancy is extremely low, but it can be prevented by using contraception or abstaining from intercourse during pregnancy.

Sources: (Cleveland Clinic) (Healthlline)

See also: Things you cannot do while pregnant

© Shutterstock