A Texas mom gave birth to 'twin' boys in October of 2021, but these twins were conceived approximately a week apart, a rare situation known as superfetation.

Wait, getting pregnant when you're already pregnant?

It's a thing, though rare, and a Ft. Worth, Texas mom became pregnant and then about a week later conceived again. She gave birth to the boys, who are thriving, in October of 2021.

In March of 2021, Cara Winhold and her husband Blake found out they were pregnant. In their ultrasound about five weeks later, they saw one baby developing.

Sadly, Winhold had a history of recurrent miscarriage, and so her doctors were watching this pregnancy closely in an attempt to do whatever they could to ensure she didn't lose the baby. They asked her to come back for another ultrasound at two weeks to check the baby's growth and make sure all was still well.

Imagine her and her husband's surprise as they saw at the follow-up that there was another sac and another growing baby in it. In an interview with The Daily Mail, Winhold said that on her first scan, she saw the sac with one baby and when she went back two weeks later there was another little tiny sack in the corner with another baby in it. She said Baby A seemed more developed, while the other one was like a dot on the screen.

Cara had suffered multiple pregnancy losses before, with her most current just a month before she conceived her sons Cayden and Colson. She nearly died with one, as she bled out so much. Her doctors wanted to follow her closely when she became pregnant so soon after her last miscarriage, and that's how they knew the timing of the conception for the second baby.

What Is Superfetation?

So, just what is superfetation? In a nutshell? It's when a second pregnancy occurs in the middle of a concurrent pregnancy--two completely different conceptions within a short amount of time.

It's rare, with about .3% of pregnant women having it occur. That said, clinicians believe that when it does occur, one 'twin' may be lost, and so there's no real way to know just how often it happens. To date, there are about 10 cases in medical literature.

While there are few cases of superfetation being available for study and description in medical literature or research, the bulk of those reported are often associated with those who are undergoing fertility treatments like artificial insemination (IUI) or in-vitro fertilization (IVF). In IUI (intrauterine insemination) scenarios, a woman's ovaries have been stimulated to produce more than one viable follicle to become an egg. Typically, though, only one to two follicles make it that far. Sperm is inserted and if an additional follicle that matured to a dropped egg meets up with sperm that survived long enough to fertilize it, superfetation can occur.

With IVF, already conceived embryos are transferred into a woman's uterus but if the woman ovulates as well, and releases an egg that is fertilized by sperm in the weeks following her transfer (provided the transfer was a successful transfer where pregnancy occurred) she could experience superfetation.

Neither scenario was the case for Winhold, however. She also said twins don't run in their family.

The truth is, getting pregnant in and of itself is complicated. The circumstances that need to occur for someone to get pregnant are pretty precise when it all boils down to it.

But for superfetation to happen, it's even more rare.

This is mainly due to three factors involved.

When pregnancy begins, a woman releases hormones that stop ovulation. This is why you don't have a period when pregnant, and why many women won't have a period for many months after a baby is born--they're still releasing those hormones. (This is also why many women believe you can't get pregnant right after a baby is born or you're nursing, but that is a myth.)

So for a person to continue ovulating despite pregnancy is the first rare step in superfetation.

Pretty miraculously, that second egg needs to be fertilized by sperm. It's already pretty tough for sperm to make it through the fertilization process on a good day, but when a woman is pregnant, mucus builds up in her cervical canal. This is the 'mucus plug' that we all know about, and this is what makes that sperm getting through even more an improbable event.

But even more rare--if the first two odds of superfetation are defied, the fertilized embryo has to implant in the uterus. Even in cases of IVF where a hand-picked embryo is transferred, there is no guarantee it will implant and continue to grow. In the case where an embryo is already implanted and growing--taking up space in the not-yet-stretched uterus, there just may not be adequate spacing or environment for the implantation of a second embryo. When a woman is ovulating, hormones to help implantation are created (or in fertility treatments, added) and if she's already pregnant, she won't make or release those. That makes the implantation process even more difficult than it already would be, and again, adds to the rarity of another, separate pregnancy occurring.

That all said--if all the stars align and two pregnancies DO occur at the same time...the growing babies will be two different gestational ages. Traditional 'twins', whether identical or fraternal, develop from two fertilized eggs that were released and fertilized at the same time, meaning they're the same gestational age throughout the pregnancy.

Winhold said that her doctors surmise she most likely ovulated twice, released two eggs, and they were fertilized at two different times--about a week or so apart.

When the babies were born, they were 35w 2 days. Colson was slightly larger than Cayden. Colson was Baby A, who had been conceived first, and at their six-month checkup, still outweighed him--by four pounds. Still, both babies are thriving and their big brother Wyatt, 3, is thrilled with them.

Congratulations to the whole incredible family!