From: Rabbi Moshe Sofer
To: Rabbi Hersh Kunitz
A woman who saw blood during intercourse twice before her pregnancy was recognizable and once after poses a serious halachic concern. The Chasam Sofer rules leniently by relying on the Ra'avad's position that the first sighting does not count without a prior bedikah, thus leaving her with only two sightings and no established chazakah. He advises she seek medical treatment and that the next intercourse occur in the fifth or sixth month of pregnancy when bleeding is less likely.
Source: Shu"t Chasam Sofer YD §164