and the womb agitated, there occurs in it a sort of tickling sensation (CFO, pt. 6)

So you were wondering, were Baker and Bellis the first to propose that orgasm aided fertilization? In fact, the Hippocratic school agreed with them, at least according to McLaren (1990). A Hippocratic medical text called On Generation also includes this charming description of the orgasm.

I assert that when the genitals are rubbed and the womb agitated, there occurs in it a sort of tickling sensation, and the rest of the body derives pleasure and warmth from it. The woman also has a discharge that flows into the womb so that the womb becomes moist, sometimes the outside of the womb too when the opening of the womb.[From Lonie (1981) as quoted by McLaren]

Unfortunately, McLaren does not quote the part of the text that describes increased likelihood of fertilization directly, and I can’t find an online version of the treatise.

Citations

Lonie, Iain M., ed. 1981. The Hippocratic treatises, "On generation," "On the nature of the child," "Diseases IV". Berlin; New York: De Gruyter.

McLaren, Angus. 1990. A history of contraception: from antiquity to the present day, Family, sexuality, and social relations in past times. Oxford, UK; Cambridge, Mass., USA: B. Blackwell.