- The causes of monozygotic twinning are generally unknown and unidentified. No one really knows why an egg splits; technically it's a malfunction of the normal development process.
- There's no hereditary trait that makes it more likely for you to have identical twins. Identical twins do NOT run in families. Although there are families with a high incidence of identical twins, it is due to chance, coincidence, or plain good luck.
- Identical twins represent about a third of all twins. Dizygotic twins are twice as common as monozygotic.
- Birth rate statistics for identical twinning have remained stable over the years, despite the overall increase in twins and multiples since the late 1980's. The odds of having identical twins is about 3 in 1,000, whereas the birth rate for ALL twins is about 3 in 100.
- Identical twinning is not generally influenced by fertility-enhancing treatments like drugs or in vitro, although monozygotic twins have been produced in pregnancies that were the result of such treatments.
- Birth rate for identical twins are consistent across populations; it is the same regardless of race, geography or maternal age.
To recap a bit, I had a di/di pregnancy ("dichorionic/diamniotic"). A di/di pregnancy is a type of twin pregnancy where each twin has its own chorionic and amnionic sacs. In fact, it's the safest type of twin pregnancy to have - the babies don't need to share anything. A di/di pregnancy often results with dizygotic aka fraternal twins - BUT (and this is a big but) it also results with monozygotic (aka identical) twins. Enter Conor and Caden!