Aside knowing your genotype before marriage, there's need for one to know her rhesus factor! INCOMPATIBILTY IS A LEADING CAUSE OF MISCARRIAGE

Rhesus factor is an antigen that exists on the surface of red blood cells in most people about 85% human. It is also referred to as Rh factor, People who have the Rh have "positive"(+) blood types, such as A+,O+,or B+. are said to be rhesus factor positive, while those whose have the Rh "negative"(-) blood types, such as A-,O-, or AB- are said to be rhesus factor negative. The "+" and "-" in front of the blood group is the rhesus factor. Generally, we have A+,A-,B+,B-,AB+,AB-,O+,O-.Rhesus factor is genetic in nature. It is inherited from the parents, emphatically the father.
HOW DOES IT CAUSE MISCARRIAGE
If a Rh- woman is impregnated by an Rh+ man, there would be a problem if the baby inherits Rh+from the father. We have here what is medically called Rhesus factor INCOMPATIBILTY. The baby would obviously be Rh+. The antibodies are immediately activated to immune system. The activated antibodies would see the new Rh+ as foreign body or a threat and consequently they would be at alert to attack and get rid of the foreign body. Unfortunately as such, after this particular childbirth, the woman would keep having miscarriage because the activated antibodies would see subsequent Rh+ pregnancies as foreign bodies and would keep fighting and taking them off.
Women with Rh activated antibodies are said to be Rh sensitized and once these antibodies are activated, they can never be deactivated until the woman dies. Rh induced antibodies are activated in a Rh- woman child birth, abortion, miscarriage and ectopic pregnancy.
If a Rh- woman commits an abortion for a Rh+ man and the antibodies are activated in her system, the woman might end up child less throughout her life except if she later marries another man with the same Rh-. The possibility of a Rh-woman finding an Rh-man is slim as about 85% of human beings are Rh+. This is a warning to our young girls who commits abortion all in the name of boyfriend and girlfriend relationship.
If your a woman with Rh- and your fiance is Rh+ and you have not committed abortion for him and you don't want to leave him, then you need to take note of the following:
In order to prevent the activation of the antibodies, doctor would give women in this category an injection called RHOGAM during and after pregnancy to prevent spontaneous abortion due to Rhesus factor INCOMPATIBILTY. The injection normally administered 28 weeks into pregnancy, 72 hours after delivery, after ectopic pregnancy, miscarriage or abortion. If the injection is not administered and the antibodies are activated, they would never be deactivated again.
In many African cultures up till today, women who are so unfortunate to find themselves having serial spontaneous abortions due to Rhesus factor INCOMPATIBILTY are considered witches by some of their people. Some of the women would accuse their in-laws of being behind their predicament.
So if your a woman with Rh-, you need to be very careful. It might be difficult for you to get a husband with a Rh- because about 85% human beings are Rh+. So, in order not to find yourself in the aforementioned problem, put all that have been said at the back of your mind and go for genetic counseling. If you have a daughter or a sister with Rh-, counsel them on rhesus factor INCOMPATIBILTY and the dangers lying there in.
It should also be noted that Rh- person(man or woman) cannot receive blood donations from a Rh+ person even if they have the same blood group. The consequences of such blood transfusion is fatal. It would lead to death as the blood would cloth. This is due to the INCOMPATIBILTY in their Rhesus factor.