When does a woman become forbidden while giving birth
Question
At which point does a woman become forbidden to her husband while giving birth?
Answer
Dear …!
May you have an easy birth and mazal tov!
After the water breaks, you have to make sure that there is no blood in the water. After the escape of the cervical mucous plug, the woman becomes prohibited. If there is a cervical dilatation of more than two fingers, there is a suspicion that she is forbidden, and if this continues for a long time, one should consult an experienced rabbi.
If there are frequent birth pangs, every 3-5 minutes, one should suspect that there is blood; if this continues for a long time, one should consult an experienced rabbi.
If a woman is unable to walk unassisted, and needs help, she is considered as being in the middle of giving birth, and is prohibited to her husband.
Source
Shulchan Oruch, section Yore Dea, chapter 194