Superfetation

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Updated Mar 5, 2025 | 07:00 PM IST

Woman Discovers She Was 4 Months Pregnant Days After Giving Birth—Doctor Explains How

SummaryIt is a rare phenomenon where a second pregnancy occurs alongside an existing one. Read on to know more about it.

Dr Joe Whittington, who goes by Dr Joe on his social media platforms is a certified MD in Emergency Medicine based in Apple Valley, California is a social media medical educator. He uploads many real-life health-related stories and cases to educate general public about it. In one such videos, he featured a woman who just had her baby four days ago and found out that she was four months pregnant.

Is This Possible?

Dr Joe says, "technically, yes". This phenomenon is known as superfetation that occurs when a woman releases an egg and it gets fertilized and implanted after she is already pregnant.

He says, "Usually pregnancy changes such as hormonal changes, changes in the uterus, and the cervical mucous plug all work to prevent this. So superfetation is extremely rare with only about 10 documented cases. But, it is possible."

What Is Superfetation?

It is a rare phenomenon where a second pregnancy occurs alongside an existing one. This happens when another ovum or the egg is fertilized by sperm and implanted in the womb days or weeks later than the first one. Babies born from superfetation are often considered twins as they may be born on the same birth on the same day. However, not always does it happen. In the case that Dr Joe picked up, the baby had a difference of four months.

ALSO READ: Pregnancy Trimesters, Everything You Need To Know About It

So, How Does It Happen?

In humans, pregnancy occurs when an egg is fertilized by sperm and implants in the uterus. For superfetation to happen, a second egg must be fertilized and implanted separately while a pregnancy is already underway.

For this to occur, three highly unlikely events must take place:

Ovulation during an ongoing pregnancy – This is rare because pregnancy hormones typically prevent further ovulation.

Fertilization of the second egg – Once pregnant, a woman’s cervix forms a mucus plug that blocks sperm from entering, making fertilization extremely unlikely.

Implantation in an already pregnant uterus – Implantation requires specific hormonal changes that usually don’t occur once pregnancy has begun.

Additionally, a growing fetus takes up space, making it harder for another embryo to implant.

Because these conditions are so improbable, superfetation is considered nearly impossible in natural pregnancies. However, a few reported cases exist, primarily in women undergoing fertility treatments like in vitro fertilization (IVF). In such cases, an embryo is transferred into the uterus, but if ovulation unexpectedly occurs and the egg is fertilized, superfetation might happen a few weeks later.

Could There Be Any Complications?

The biggest complication with superfetation is premature birth. The baby maybe born before time and could have the following medical conditions:

  • trouble breathing
  • low birth weight
  • movement and coordination problems
  • difficulties with feeding
  • brain hemorrhage or bleeding in the brain
  • neonatal respiratory distress syndrome, which is a breathing disorder caused by underdeveloped lungs

Women too could have complication, which includes high blood pressure and protein in the urine, a condition called preeclampsia, and gestational diabetes.

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