The normal process of getting pregnant is an ovum is released, becomes fertilized and implants itself on the uterine lining where it eventually becomes a fetus.
However, some women can get pregnant a second time while they’re already pregnant with one baby.
A pregnancy like this is known as superfetation but is very rare and can only occur under specific circumstances.
It’s very rare in human beings because once a woman is pregnant, changes in the body’s hormone prevents her from ovulating.
However, if the woman keeps ovulating and the ovum is fertilized and gets implanted in the uterus, she can carry a double pregnancy.
The reasons why women can continue ovulating while already pregnant are not widely studied and more research is being conducted.
Moreover, double pregnancy can occur if a woman has a double uterus or if she ovulates multiple times.
In common cases, once a woman gets pregnant, the body emits hormones that stop ovulation. They also block other pregnancies from occurring.
Additionally, the cervix forms a protective barrier that prevents the sperms from penetrating.
This means, for superfetation to occur, there has to be irregular ovulation or once an ovum has already been fertilized.