Twins with two fathers are possible with heteroparental superfecundation and heteroparental superfetation. Superfecundation and superfetation and two rare events.
- Superfecundation is when there are twins from ovulation on the same day with two separate fathers.
- Superfetation happens if there is a second pregnancy from two separate ovulations; the second ovulation can occur weeks or even months after the first.
- You have to ovulate twice (dizyogtic).
- You have to have sexual intercourse with different men within a couple of days of ovulation.
Both of these events can happen on the same day or different days, as sperm can survive for up to 5 days. Multiple ovulations happen in about 1% (or more) of all ovulations, and more often when you take ovulation-inducing medications.
Superfetation happens when a woman gets pregnant again after the implantation of one fetus. For this to happen the pregnant woman must ovulate after she is already pregnant and this egg must be fertilized by another sperm. This can occur weeks or even months after the first egg is fertilized, and the result is that one fetus is more advanced in pregnancy then the other. This is an extermely rare event in humans and has been reported only a few times. Superfetation can happen with the same father or different fathers (heteroparental).