EXPLAINER: You can get pregnant while still pregnant

Bettinna Carlos’ rare pregnancy shines spotlight on one of medicine’s rarest phenomena.

Most people assumed actress and TV host Bettinna Carlos was simply expecting twins.

But when she recently revealed that her sons were actually conceived about 10 days apart—a condition known as superfetation—many Filipinos were left asking the same question: Can someone really get pregnant while already pregnant?

The surprising answer is yes—but only in extraordinarily rare circumstances.

Superfetation is one of the rarest reproductive phenomena ever documented in humans. It happens when a woman who is already pregnant releases another egg, which is then fertilized and successfully implants in the uterus. Instead of being conceived at the same time like ordinary twins, the babies develop days or even weeks apart, giving them different gestational ages while sharing the same womb.

Medical literature has documented only about 10 to 14 confirmed cases worldwide, making it a condition so rare that many obstetricians may never encounter one throughout their careers.

Why it is so rare

Human biology is designed to prevent a second pregnancy from happening.

Once an embryo implants, pregnancy hormones—particularly progesterone—signal the ovaries to stop releasing eggs. At the same time, the cervix forms a thick mucus plug that blocks sperm from entering the uterus, while the uterine lining changes in ways that make it difficult for another embryo to implant.

For superfetation to occur, all three of these natural safeguards must somehow fail at the same time.

Doctors say that combination is so unlikely that the condition is considered almost impossible under normal circumstances.

Not the same as ordinary twins

Superfetation is often confused with ordinary twins, but they are biologically different.

Traditional fraternal twins are conceived during the same ovulation cycle when two eggs are fertilized around the same time.

In superfetation, however, the pregnancies begin in separate ovulation events. One baby is already developing before the second embryo is even conceived.

This means the younger fetus is biologically less mature, even though both babies eventually have to be delivered on the same day.

Different from “twins with different fathers”

Another condition frequently mistaken for superfetation is superfecundation.

Superfecundation occurs when two eggs released during the same menstrual cycle are fertilized separately, sometimes even by different fathers.

Superfetation, on the other hand, happens across separate conception events after pregnancy has already begun and usually involves the same biological father.

How do doctors discover it?

Most cases are identified during early pregnancy ultrasounds.

Doctors notice that one fetus is significantly smaller than the other—not because of poor growth, but because it is actually younger. The developmental gap is too large to be explained by normal differences seen in twin pregnancies.

Further scans help confirm that the babies are progressing normally despite their different gestational ages.

The biggest challenge

Perhaps the greatest difficulty comes at delivery.

Because both babies share the same uterus, doctors cannot simply allow the younger fetus to remain inside after the older one is born.

Instead, obstetricians carefully monitor both babies throughout the pregnancy and choose a delivery date that offers the safest balance between allowing the older baby to reach maturity while minimizing the younger baby’s prematurity.

This is why many superfetation pregnancies result in premature births and require specialized neonatal care.

Why more cases are being reported

While spontaneous superfetation remains exceptionally rare, doctors say modern fertility treatments have made such cases slightly more likely.

Procedures such as in vitro fertilization (IVF) or medications that stimulate ovulation may occasionally create circumstances in which a second conception becomes possible shortly after an initial pregnancy has already begun.

Even so, the condition remains one of the rarest events in reproductive medicine.

Carlos’ experience may have introduced superfetation to many Filipinos for the first time, but for medical experts, it serves as a remarkable reminder that while human biology follows well-established rules, nature can still produce extraordinary exceptions.

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