The human body seemed to be a total mystery, and scientists are still learning how it works. One of the most common misconceptions is that it is impossible for a pregnant woman to get pregnant again. This condition called superfetation may be rare, but it does happen.

This topic was addressed recently by New York Times after a curious reader asked if it is possible for two fetuses to develop at varying stages at the same time.

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Last year, BBC News reported that an Australian woman gave birth to twins, but they were conceived 10 days apart. It is not common for women to release another egg after conception although the monthly cycle of ovulation normally stops upon pregnancy. There are only 10 known cases of superfetation across the world.

Connie Hedmark, an obstetrician from Marquette General Hospital in Michigan, explained that superfetation is very remarkable. He said that a woman's system is usually shut down by a pregnancy hormone that is why it is impossible for her to undergo ovulation during pregnancy.

According to Medical Daily, some doctors do not believe it because it is not within the bounds of the biological norm. Jason James, M.D. and medical director at FemCare Ob-GYN in Miami said that superfetation might result in unequal development and growth of twins, but they are of the same gestational age.

Although doctors are unsure about why this occurs, there is a theory that if the implantation of the first embryo is delayed, hormone spike is subdued.