There was a lot of research done on the Pill when it was first made available to American women on a mass scale in the early 1960s. The big takeaway, relevant since use was primarily restricted to already-married women, is that women on the Pill had a higher “coital frequency” than women not on the Pill and that pre-Pill, women were in fact having less sex with their husbands over time to avoid pregnancy. Marrying young was resulting in not as much sex after the first ten years, due to desire for limiting fertility rather than lack of interest according to separate surveys of husbands and wives.
But once the Pill was introduced, women who went on it had more sex and of course had fewer children. It sure seemed like cake was being had and eaten too. This is particularly interesting given that decades later research on women taking the Pill showed it to be heavily correlated with reduced sex interest in women and lower libido. Thus we have the origin story for the mythical housewife who wasn’t that into it but just trying to keep her man satisfied.
The other thing I just remembered about this is that the Pill was the only contraceptive with a substantial increase in sex-having vs non-Pill users. Sterilizations on either male or female side, condoms, jellies, and the like never showed people utilizing them to have more sex than people avoiding contraceptive use.