Tosefta untuk Ulangan 21:16

One who is born after the fallen (i.e., a stillbirth), even though [the stillborn] emerged in the eighth month or in the ninth month [of pregnancy], [or when] its head emerged [it was already] dead, [the subsequent newborn male] is a first-born for purposes of inheritance but is not a first-born for purposes of [redemption from] a priest, as it is said (Deut. 21:16), "He may not treat as a first-born the son of the beloved [wife], etc." This is the general rule: Anything whose head and most of its body emerged alive exempts that which comes after it from the [status of] first-born, but not the five selas of the son (i.e., the redemption price paid to the priest). Two wives of two men that had never given birth, and they gave birth in a hiding-place (e.g., in times of war (Jastrow)), and one of them died, the second one is a first-born for purposes of inheritance, but is not a first-born for purposes of the priest. [If] she and a priestess gave birth -- [or] she and a Levitess, [or] she and a woman who had already given birth -- to two males, [the one that is considered hers] is a first-born for purposes of the priest but is not a first-born for purposes of inheritance. [If] one of them died, or if they were male and female, [the one that is considered hers] is neither a first-born for purposes of inheritance, or for purposes of the priest.