Dan Greenberg (The Arkansas Project) notes that the report of United States v. Dickinson, 1 Hempstead 1, 2 n.1 (Ark. Terr. 1820) — possibly the very first reported case from the Arkansas Territory — says the following:
The old notion that if the woman conceived, it could not be a rape, because she must in such cases have consented, is quite exploded. 1 Hale, 631; 1 Hawkins, ch. 41, sec. 8; 1 East, P.C. ch. 10, sec. 7, p. 445; 1 Russ. on Crimes, 677. Impregnation, it is well known, does not depend on the consciousness or volition of the female. If the uterine organs be in a condition favorable to impregnation, this may take place as readily as if the intercourse was voluntary. Taylor’s Med. Jurisprudence.
To be sure, this passage ought not be accused of originality — Hawkins’ Pleas of the Crown (1716) states that, though “it hath been said by some to be no Rape to force a Woman who conceived at the Time; for it is said, That if she had not consented, she could not have conceived,” “this Opinion seems very questionable.”
Needless to say, ancient authorities count for more in law than in medicine, but my understanding is that medicine has not reached a different result than that given in the report of United States v. Dickinson.