It's normal to want to understand why a miscarriage happened, and it's frustrating that definitive answers are few and far between. After hearing about the need for RhoGAM after a miscarriage, many Rh negative women wonder whether that blood type might play a role in causing the miscarriages.
The short answer is that no, being Rh negative by itself does not cause miscarriage or pregnancy loss. Women who are Rh negative, who have kept up to date with recommended RhoGAM shots, and who do not have antibodies against Rh factor do not face increased risk for pregnancy loss due to having Rh negative blood.
Assuming a woman does become sensitized to Rh factor, however, the primary risk is not of pregnancy loss but of Rh incompatibility issues with any future baby to whom she gives birth.
In Rh-negative moms who are sensitized to Rh factor, there's also an increased risk of stillbirth due to a condition called immune hydrops fetalis that can develop in the second and third trimesters -- but this condition is not a factor in first-trimester miscarriages. The most common cause of first-trimester miscarriages is chromosomal abnormalities in the baby.
If you are Rh negative and concerned that you might be sensitized to Rh factor, talk to your doctor about having a blood test done to check for anti-Rh antibodies. If the test comes back negative, then your Rh status will not bring any increased risks in a future pregnancy (but do continue to get RhoGAM shots per your doctor's recommendations). Mothers who are sensitized to Rh factor should be vigilant about seeking prenatal care in any subsequent pregnancy.
Sources:
A.D.A.M. "Rh incompatibility." About.com A.D.A.M. Healthcare Center 18 Aug 2006. Accessed 27 Nov 2007.
