What Is A Superfetation Pregnancy?

Not many people realize it, but getting pregnant, from a statistical standpoint, can be considered a miracle. Many people understand the process, yet they may not truly realize what goes into becoming pregnant (and the things you should never do during pregnancy).

First, when a female baby is born, they have between 1 and 2 million eggs. Once she hits puberty and can begin to conceive children, that number reduces to between 300,000 and 400,000, according to Healthline.

To become pregnant is a complicated process, explains USCF Health. The sperm travels through the vagina and cervix (an environment that can change depending on hormonal control, possibly destroying the sperm) and then through the fallopian tubes.

Once a month, an egg is released through ovulation and the release of sperm needs to be timed properly so the sperm meets the egg. Contact is random and the egg can only be fertilized for between 12 to 24 hours.

Fertilization occurs in the fallopian tube where the egg then races to the uterus where it will develop into an embryo. The embryo implants itself in the uterus. This is the stage where the woman considers herself to be pregnant.

With these steps in mind, a woman has a 15 to 25% chance of getting pregnant every month if she's trying to do so, according to HealthPartners. Such a complicated system can have kinks, right? Specifically, what happens if you get pregnant while you're already pregnant? Is that possible?

Getting pregnant while already pregnant is called superfetation

Let's get this out of the way first. Yes, it's technically possible to become pregnant while already pregnant. It even has a name — superfetation. However, the chances of superfetation are so low that every known case of it is basically considered a medical miracle.

It's so rare because your body tries its best to not get you pregnant again when you're already pregnant. When you are pregnant, a hormone is released called hCG which shuts down the connection between your ovaries and pituitary gland that is required to ovulate and therefore become pregnant, according to Self. So how is superfetation possible?

A woman would need to ovulate again, her cervix would need to be open enough to let sperm through (a cervix is firmly shut during pregnancy to prevent a premature birth), and the timing would need to be right to allow sperm to meet the egg. Needless to say, superfetation can only happen very early on in pregnancy.

The chances of superfetation are so close to impossible that almost all the cases of it occurring happened to women who were undergoing fertility treatments, according to Healthline.