Superfetation occurs when a second fertilized ovum implants in a uterus already containing a pregnancy of at least 1 month (69). Superfetation has been suggested in some cases in which the twins are markedly discordant for birth weight, supposedly due to different gestational ages (69,81).

How often does superfetation happen?

Though rare, this condition is believed to affect as many as 0.3% of women but often one twin is lost so the true numbers are not known.

Can you get pregnant while 3 months pregnant?

And yet – at least for a handful of women – it has happened. In an odd phenomenon known as superfetation, a pregnant woman releases an egg a few weeks into her pregnancy. The second egg is fertilized, and the woman is then pregnant with two babies simultaneously.