Superfetation and superfecundadtion are two different events of twin pregnancies. In superfetation, one fetus implants on top of another fetus and both are at different stages of gestational age. With superfecundation, there are twins but they are at the saame gestational age, and there can be either two or the same father.
Superfetation is the simultaneous occurrence of more than one stage of developing offspring in the same animal. In mammals, it manifests as the formation of an embryo from a different cycle while another embryo or fetus is already present in the uterus. When two separate instances of fertilisation occur during the same menstrual cycle, it is known as superfecundation.
Superfetation is claimed to be common in some species of animals, but is extremely rare in humans. In mammals, it can occur only where there are two uteri, or where the estrous cycle continues through pregnancy. The risk with superfetation in humans is that the second baby is often born prematurely, which can increase its odds of experiencing lung development problems.
Superfetation happens when twins are conceived many days or weeks apart from two separate ovulations and from two different fathers or the same father, the second one after the first has already implanted. Superfecundation are twins with different fathers but ovulations the same day.Superfetation happens when twins are conceived weeks apart from ovulation happening on different days. For superfetation to happen, two things have to happen:
1. You have to ovulate twice (dizyogtic) several weeks apart
2. You did get pregnant again after the first fetus has already implanted
The result of two pregnancies happening weeks apart is that the two twins are in different developmental stages and one fetus is more advanced in pregnancy then the other. This is an extremely rare event in humans and has been reported only a few times. Superfetation can happen with the same father or different fathers.
Superfecundation happens when twins are conceived by different fathers, usually within a couple of days from having sex with different men but from ovulation happening on the same day or within a few days.