Predisposing factors

Predisposing factors

The cause of monozygotic twinning is unknown. Fewer than 20 families have been described with an inherited tendency towards monozygotic twinning (people in these families have nearly a 50% chance of delivering monozygotic twins). Some evidence suggests that the environment of the womb causes the zygote to split in most cases.
Dizygotic twin pregnancies are slightly more likely when the following factors are present in the woman:
She is of African descent (especially Yoruba} Between the age of 30 and 40 years Greater than average height and weight Several previous pregnancies. Women undergoing certain fertility treatments may have a greater chance of dizygotic multiple births. This can vary depending on what types of fertility treatments are used. With in vitro fertilisation (IVF), this is primarily due to the insertion of multiple embryos into the uterus. Some other treatments such as the drug Clomid can stimulate a woman to release multiple eggs, allowing the possibility of multiples. Many fertility treatments have no effect on the likelihood of multiple births.
There is also speculation that the West African predisposition to twinning is due to the large amount of yams in their diet. These yams contain phytoestrogen, this natural hormone may stimulate the ovaries.