http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10641935&dopt=Abstract
A case of superfecundation and dual paternity in a twin pregnancy is presented. Placental abruption developed at week 33 of gestation and the two boys had to be saved by emergency cesarean section. As they shared one placenta, had almost identical weight and had the same sex, they were assumed to be monozygotic. However,
a subsequent paternity suit led to the conclusion, based on DNA-analysis, that the twin brothers had been fathered by two different men. Obstetrical implications are discussed."
The implications of such a scenario are rather interesting in respects to CS and custody. Twins could each have different visitation schedules (one supervised, one shared custody), different levels of support, and different judges making determinations about their cases (this might occur if each father proactively and independently files for paternity establishment). Also, I would presume that in ALL fraternal twin births, BOTH twins would need to be DNA tested for paternity establishment. If only ONE twin is positive for the father testing, for example, would mom need to reimburse dad for the cost of the second test? Can just ONE of the fathers be made responsible for the birthing costs, if no paternity has been established for twin 2, for example?
If dad of twin 1 works days and can provide daytime care for his child, would he then get daytime custody of one twin, while the other goes to daycare? Etc.