Understanding Rh Factor Inheritance: Explaining Rh- Negative Babies

Question
I AM O + MY HUSBAND IS O+ OUR FIRST TWO CHILDREN ARE O+ BUT OUR THIRD CHILD IS O RHESUS D NEGATIVE IS THERE A REASON FOR THIS

Answer
There are two alleles for each Rh factor. An allele is an alternative form of a gene. An Rh factor refers to the "+" or "-" part of the blood type. Since there are two alleles and your third child is Rh- (or D-), that would mean you and your husband have the following alleles:
you: Rh+ / Rh-
your husband: Rh+ / Rh-.
With your third child, you both passed along the Rh- allele. This resulted in the child being Rh-. For your first two children, one of two things happened. Either you both passed along the Rh+ allele, or one of you passed along the Rh+ allele and the other passed along the Rh- allele. If someone ends up with two Rh+ alleles, they are Rh+. When someone ends up with an Rh+ allele and an Rh- allele, they are Rh+. Let me know if you have more questions.

- Beth