A twin pregnancy means that there are two fetuses in the uterus. This is rare and may be due to family history, fertility treatments, or other factors. A twin pregnancy increases the risk of complications for the pregnant woman and the fetus, which is why more frequent prenatal check-ups are necessary.
Twins are two offspring produced by the same pregnancy. Twins can be either monozygotic, meaning that they develop from one zygote, which splits and forms two embryos, or dizygotic, meaning that each twin develops from a separate egg and each egg is fertilized by its own sperm cell.