In the earlier part of the 19th century, manuals advised women to have orgasms as a way to encourage conception, but manuals in the 1870s started taking the opposite view, telling women that if they orgasmed, they would be too weak to conceive. If the couple consulted a "marriage manual" like this from that period, they might think that she needed to avoid orgasms or anything that could bring on lustful feelings in order to conceive. If it was suspected that the male was impotent or was having problems performing, there were a variety of treatments. Electricity was used to help give a man an erection, special diets were prescribed, sometimes drugs were used (occasionally in an injection), or occasionally a measure such as circumcision was recommended. Most physicians by this time, though, seemed to realize that male impotence was a psychological problem, and generally had more effective treatments.
I couldn't find a source right at my fingertips, but I believe that they had a pretty good sense of how a woman's cycle worked by the 1880s. Although doctors were pretty wrapped up in prescribing medications and trying new-fangled techniques, a midwife might advise the couple to pay close attention to the woman's cycle and try to time intercourse accordingly, as EllenG suggested.
Now reading back over your post, I realize that you don't specify which country you are most concerned with.
My research is in 19th century America, and so in that area, a couple of books that I can recommend:
D’Emilio, John and Estelle B. Freedman. Intimate Matters: A History of Sexuality in America. New York: Harper & Row, 1988.
Haller, John S. and Robin B. Haller. The Physician and Sexuality in Victorian America. Urbana, Ill.: U of Illinois Press, 1974.