The Rhesus factor (Rh) plays a great role in conception and childbirth especially on the side of the female.
SCENARIOS
Scenario #1
A man with Rh+ marries a woman with Rh+ have no genetic issues with conception and childbirth.
Scenario #2
A man with Rh- marries a woman with Rh+. These two will equally have no genetic issues with conception and childbirth.
Scenario #3
A man with Rh- marries a woman with Rh-, they also will have no problems genetically.
Scenario #4
But the issue props up when a man with Rh+ marries a woman with Rh-.
In the woman’s first pregnancy (whether she carries to term or not), most especially during childbirth, there’s an exchange of blood between the mother and the foetus. As such, the mother’s body takes not of the Rh factor of the child (Rh+) and signals it down as a foreign body (antigen) and then produces soldiers (antibodies) to fight against any such antigen that enters the body.
Therefore in subsequent pregnancies, the antibodies will always flag down the Rh+- antigens and seek to destroy them leading to miscarriages.
Modern medicine, however, has been able to come up with a drug which is given to the woman after her first conception (whether she carries to term or not). This drug is injected into her body immediately after childbirth or a miscarriage to fool the body into believing that there is no Rh+-antigens present in the bloodstream and thus no antibodies are formed to ensure successful subsequent pregnancies.