Superfecundation is the fertilization of two or more ova during the same ovulatory cycle, by separate coital acts. When the fertilization is by sperm from different fathers, it is called heteropaternal superfecundation.
In other words, fraternal twins can have different fathers.
According to this article in the medical literature, approximately 1 in 12 sets of dizygotic (fraternal) twins result from superfecundation.
The same paper (1993) estimates that 1 in 400 sets of fraternal twins born to married, white American women result from heteropaternal superfecundation.
Heteropaternal superfecundation has been suggested as an explanation for the "black and white" twins I wrote about here. There's been no official word on the mother's sexual history, or whether paternity tests were done, so it remains speculative.
And maybe the twins who married each other without realizing they were related had different fathers, and were merely half-siblings. Although I doubt that would have been much consolation.
This blog is so educational! Never heard the word superfecundation and can't wait to use it in a conversation... :-)
Posted by: Tessa | 21 January 2008 at 10:36 AM
It could also be a result of sloppy fertility treatments.... This was something I really worried about before the boys were born - Jelle once joked about the possibility of them being Chinese. Not something I found amusing!
Posted by: Hilary | 21 January 2008 at 01:19 PM
Hilary,
Here's a Dutch example of exactly what you're referring to: http://www.msnbc.msn.com/id/9438648/
Posted by: Martina | 21 January 2008 at 01:38 PM
Just read the link - wow... the mother is probably viewed as loose and the father is pitied. Very Dutch though, the way people on the street responded - gotta love their directness!
You should add superfetation to the above post. Can you imagine going through labour 2 months in a row?
Posted by: Hilary | 22 January 2008 at 12:32 PM
Superfetation is next Monday's post. Don't give anything away . . .
Posted by: Martina | 22 January 2008 at 07:13 PM
This happened to me with my twins with the exception that they were both in the same bag and there was only one placenta. The girls were totally different all the way around. One blonde with green eyes & the other brown with brown.Go figure!
Posted by: Arlene | 17 December 2009 at 11:41 AM