What factors increase the probability of having fraternal twins

As well as having a genetic basis, which could be the case if there are various sets of non-identical twins in the family, there are other factors that can increase the odds of having non-identical twins. Amongst these:

• Maternal age between 35-39 years old: as the ovarian reserve diminishes, levels of FSH increase. This can lead to an increased possibility of multiple ovulation.
• Births: having had previous births is also related to a higher probability of having fraternal twins.
• Geographical location: The rate of dizygotic twins (non-identical twins) shows regional variations, probably to due a genetic factor.
• Body build; a body mass index (BMI) of over 30, and a greater height have been associated with an increased probability of having fraternal twins.
• Assisted reproduction techniques (ART): for different reasons, such as the transfer of more than one embryo into the uterus, ART increases the chances of having non-identical twins.

However, it is important to know that multiple pregnancies carry with them increased risks, as much for the mother as for the babies. For this reason, ART is taking measuures, such as the transfer of a single embryo during each embryonic transfer, to reduce the number of multiple pregnancies.