The occurrence, known as heteropaternal superfecundation, is rare with few publicly known about.
It happens when a woman’s eggs are fertilised by two men within a short period of time.
- ‘Superfecundation’ refers to the fertilisation of multiple eggs from separate acts of intercourse, and ‘heteropaternal’ means they are fertilised by more than one father
- It can happen when a woman produces multiple eggs in one ovulation period and they are fertilised by different men within a few days
- It can also happen if a woman ovulates twice within a short period of time and both eggs are fertilised by different men
- Reported cases are very rare – apart from the one in 2015 involving twin girls in New Jersey, only the third such case known to ever occur in the US. The last case was a pair of Vietnamese fraternal twins confirmed to have different fathers.
- Turkish media reported a similar case in 2010 involving twin boys.