The Mishna on our daf discusses a case in which a man divorces his wife claiming that she is an aylonit – a woman who cannot conceive. The rishonim point out that theoretically a man need not divorce a woman with such a condition; since one of the essential points of marriage is having children, once a man discovers that his wife cannot bear children he can claim mekah ta’ut – that the entire marriage was predicated on a mistaken assumption – and have the marriage annulled. Rashi suggests that although a person can make such a claim, in practice people do not do so because, “En adam oseh be’ilato be’ilat zenut – a person does not want to make the relations that he had with his wife into promiscuous acts”. Tosafot simply explain that the woman was not definitely an aylonit bur rather had only some of the indicators that pointed to that condition.
From the detailed discussions in the Gemara – mainly in Massekhet Yevamot – it appears that an aylonit suffers from a genetic defect that does not allow her to have children. This is a different categorization than an akarah – a barren woman – whose physical and sexual development is ordinarily normal, but cannot have children because of some other deficiency or impediment. From those descriptions it appears that an aylonit can be recognized by certain unique physical traits, including a lack of secondary sex characteristics like pubic hairs. Furthermore, it appears from the Gemara that there are different types of aylonit, ranging from women who have an overabundance of male hormones to those who suffer from Turner syndrome, where only one X chromosome is present and fully functioning. Approximately 98% of all fetuses with Turner syndrome spontaneously abort; the incidence of Turner syndrome in live female births is believed to be about 1 in 2500.
Within Jewish law there are many discussions about the status of an aylonit, mainly because of the lack of secondary female sex characteristics and because they develop at a relatively advanced age. Thus we find questions about when an aylonit is considered to have reached the age of adulthood, which halakha ordinarily defines as physical maturity.