Can you get pregnant while still pregnant? Yes, it's called superfetation and yes, it's super rare

It may sound impossible, but in extremely rare cases, a woman can become pregnant while she is already pregnant.

According to Kuya Kim, the condition is called superfetation, a phenomenon so uncommon that only around 10 documented cases have been reported worldwide.

Dr. Mae C. Syki-Young explained that superfetation happens when a second pregnancy occurs during an existing one.

"Superfetation means you're already pregnant and have been diagnosed as pregnant, then you become pregnant again. It's a pregnancy within an existing pregnancy," she said.

What is superfetation?

Superfetation is a rare condition in which a woman conceives a second baby while she is already pregnant.

As a result, two fetuses develop in the uterus at the same time. But because they are conceived weeks apart, the two fetuses have different gestational ages.

Under normal circumstances, this should not happen because the body naturally prevents another pregnancy once conception occurs.

Normally, ovulation stops during pregnancy, preventing the release of another egg. A mucus plug also forms in the cervix, making it difficult for sperm to enter the uterus. At the same time, the uterine lining changes to support the growing embryo and is no longer receptive to another implantation.

For superfetation to occur, all of these natural mechanisms would have to fail. The ovary would need to release another egg, that egg would have to be fertilized by sperm, and the newly formed embryo would have to successfully implant in the uterus despite an ongoing pregnancy.

Why does it happen?

Doctors still don't have a clear explanation for why superfetation occurs.

"It cannot be explained — that's the thing. That's why it's very, very rare. Normally, the body shuts everything down. Once you're pregnant, ovulation stops," Dr. Syki-Young said.

For example, when a woman is five weeks pregnant, she should no longer be ovulating. But in the rare event that another egg is released, fertilized, and successfully implanted, a second embryo can begin developing alongside the first.

This results in two babies growing in the same uterus, but with different gestational ages.

Just how rare is it?

There are only around 10 documented cases of superfetation, Dr. Syki-Young said, adding she's never encountered a case herself.

"I haven't seen one. It's very difficult to document. Superfetation is extremely rare—its chances are almost zero. Sometimes it can appear to be twins where one baby is simply growing more slowly because a baby's gestational age is estimated based on measurements," she said.

Experts say that most documented cases have been linked to Assisted Reproductive Technology (ART), although superfetation remains exceptionally rare even among women undergoing fertility treatments.

The condition is more commonly observed in certain animals, including rodents, small mammals, and some species of fish.

Is superfetation the same as having twins?

Although both involve two babies developing in the uterus and are often delivered at the same time, superfetation is different from a twin pregnancy.

In twins, both embryos are conceived during the same menstrual cycle. In superfetation, however, the embryos are conceived at different times, resulting in different gestational ages.

For this reason, babies born through superfetation are not technically considered twins from a medical standpoint.

Is it dangerous?

Like twin pregnancies, superfetation is considered a high-risk pregnancy because the mother is carrying two babies.

However, the biggest challenge is deciding when to deliver them.

"With superfetation, you're carrying two babies, so the care is similar to that of twins and it's considered high-risk. But the challenge is deciding when to deliver because one baby is older while the other is younger," Dr. Syki-Young said.

According to Dr. Syki-Young, doctors aim to allow the older baby to reach around 38 to 39 weeks of gestation whenever possible.

By then, the younger baby may have reached 35 to 37 weeks, an age at which babies generally have a good chance of surviving outside the womb.

Because of this, regular prenatal checkups, proper nutrition, and close monitoring by an OB-GYN are essential. The goal is to safely deliver both babies while protecting the mother's health. — Carby Basina/LA, GMA News