Halakhah do Królów II 20:23

From the laws of the commandment is that which they, may their memory be blessed, said (Yevamot 78a) [that if] an Egyptian marries [another] Egyptian and she converts while she is still pregnant, the offspring is called the second [generation], as it states, "Children that will be born to them, etc." - and the verse makes it dependent on the birth; and [that if] an Ammonite convert marries an Egyptian woman, the offspring is an Ammonite, [but in the case of] an Egyptian convert that married an Ammonite woman, the offspring is an Egyptian. This is the general principle: With the [gentile] peoples alone, it goes after the males, and like we find that Scripture relates them to the males, as it is stated (II Kings 20:12), Baladan the son of Baladan. [But if] they [both] convert, it goes according to he less [advantageous]. And the rest of the details of the commandment are elucidated in the eighth chapter of Yevamot and at the end of Kiddushin (see Tur, Even HaEzer 4).