A double pregnancy, also known as superfetation, is a rare phenomenon where a second pregnancy occurs while a woman is already pregnant. In superfetation, another ovum (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 since they may be born during the same birth on the same day. However, they are two separate pregnancies.

Superfetation is rare in humans and observed in animals much more frequently. There are only a few cases of supposed superfetation in the medical literature. Most cases occurred in women undergoing fertility treatments such as in vitro fertilization (IVF). For superfetation to happen, the following conditions must be met:

• Ovulation (release of an ovum by an ovary) during an ongoing pregnancy, which is incredibly unlikely because hormones released during pregnancy function to prevent further ovulation.
• The second ovum must be fertilized by a sperm cell, which is also unlikely because once a woman is pregnant, their cervix forms a mucus plug that blocks the passage of sperm.

Its important to note that superfetation is nearly impossible in all pregnancies, including those involving assistive reproductive technology.

If a woman experiences superfetation, there may be some complications. For example, if one fetus matures more rapidly than the other, the younger fetus may be born prematurely. In such cases, a healthcare provider may recommend a planned C-section to increase the chances of a healthy delivery for both babies without complications.

In conclusion, a double pregnancy or superfetation is a rare phenomenon where a woman becomes pregnant a second time while already pregnant. It is nearly impossible in all pregnancies, including those involving assistive reproductive technology. If it does occur, it can lead to some complications, and healthcare providers may recommend a planned C-section to increase the chances of a healthy delivery for both babies without complications.