This is an excerpt from the FDA website from 2010 on finasteride (https://www.accessdata.fda.gov/drugsatfda_docs/label/2011/020788s018lbl.pdf). Dr. Ed Epstein, from the Bosley Medical Group is a urologist by training and has kept up on the latest information on the impact or lack of impact of the drug finasteride on risks for an unborn fetus. “I am not aware of new studies on amounts of finasteride in semen or vaginal absorption data” that reflect increased risks for fetal abnormalities induced by finasteride other than what is written in the FDA white paper referenced above.
Some doctors are concerned that patients who go on finasteride should get semen analysis to keep track of semen levels in case these level dropped while a patient was on the drug finasteride. Dr. Epstein said: “Concerning getting semen analysis on child bearing age men starting finasteride, I totally disagree. Typically a male infertility workup is suggested after one year of unprotected intercourse. The subgroup of men who have low sperm counts on finasteride are those with preexisting conditions and appear to respond to discontinuation of finasteride.”In other words, he feels that a young man should not worry about either low semen counts caused by finasteride, but that they could always stop the drug and if there was a causal relationship, it would reverse. He also suggested than men with low sperm counts while on finasteride, probably had it before they started the drug and should get any low sperm count evaluated by an expert.
The FDA while paper referenced above showed that studies on semen in sperm were either not present or when present were so low as it not cause a risk to a pregnant woman or a woman who is expecting to become pregnant. “Semen levels have been measured in 35 men taking finasteride 1 mg/day for 6 weeks. In 60% (21 of 35) of the samples, finasteride levels were undetectable (<0.2 ng/mL). The mean finasteride level was 0.26 ng/mL and the highest level measured was 1.52 ng/mL. Using the highest semen level measured and assuming 100% absorption from a 5-mL ejaculate per day, human exposure through vaginal absorption would be up to 7.6 ng per day, which is 750 times lower than the exposure from the no-effect dose for developmental abnormalities in Rhesus monkeys and 650-fold less than the dose of finasteride (5 ?g) that had no effect on circulating DHT levels in men”Another opinion can be found here: https://www.medpagetoday.com/Endocrinology/Infertility/41424