It is not true that 1.7% of the population is ‘born between the sexes’. The proportion of people with DSDs (‘intersex’ conditions) is 0.018%.
Conditions in which chromosomal sex is inconsistent with phenotypic sex, or in which the phenotype is not classifiable as either male or female, occur in 0.018% of the population .
The claim that 1.7% of the population is ‘intersex’  includes conditions which most clinicians do not recognize as intersex , and is often wrongly used to back up the ideological assertion that ‘sex is a spectrum’, or that biological sex is not dimorphic.
The philosopher Kathleen Stock points out that she would be considered as “intersex” under Fausto-Sterling’s “preposterously over-demanding conditions on sex category membership”, as she lost an ovary in early adulthood , which would count as “intersex” according to Fausto-Sterling.
 Sax, L. (2002). How common is intersex? a response to Anne Fausto-Sterling. J Sex Res. 39 (3): 174-8. [Link]
 Fausto-Sterling, A. (2000). Sexing the Body: Gender Politics and the Construction of Sexuality. New York: Basic Books. [Link]
 Stock, K. (2021). Material Girls. Little, Brown Book Group: p.56 [Link]