How frequent is heteropaternal superfecundation?

@article{Wenk1992HowFI,
  title={How frequent is heteropaternal superfecundation?},
  author={Robert E Wenk and Terry Houtz and Michael A Brooks and Francis A Chiafari},
  journal={Acta geneticae medicae et gemellologiae},
  year={1992},
  volume={41 1},
  pages={43-7}
}
A newly discovered case of heteropaternal superfecundation (HS) is reported. Three HS cases were found in a parentage test database of 39,000 records. The frequency of HS among dizygotic twins whose parents were involved in paternity suits is 2.4%. Although the study population appears similar to the general population with respect to twinning data, inferences about the frequency of HS in other populations should be drawn with caution.