I found this:
Definition of consanguinity
In clinical genetics, a consanguineous marriage is defined as a union between two individuals who are related as second cousins or closer, with the inbreeding coefficient (
F) equal or higher than 0.0156 (Bittles
2001), where (
F) represents a measure of the proportion of loci at which the offspring of a consanguineous union is expected to inherit identical gene copies from both parents. This includes unions termed first cousins, first cousins once removed and second cousins.
In some communities, the highest inbreeding coefficients are reached with unions between double first cousins practiced among Arabs and uncle–niece marriages practiced in South India where (
F) reaches 0.125 (Hamamy et al.
2011) [Fig.
2].
https://tinyurl.com/hsqavhm
But then Jaime and Cersei are siblings. Shouldn't Cersei's latest kid have three heads or something? How many of her kids were Jaime's?