One of the most important aspects of an obstetric history is the identification of genetic diseases that exist in the family. Since many of these conditions can skip generations and can be inherited in different ways, it's important to note them and, if necessary, obtain more detailed information about the family member(s) who are affected.

Some examples:

Mental retardation: most cases of mental retardation do not have any inheritable component. However, some conditions such as Down syndrome and Fragile X syndrome in other family members (on either your side or the baby's father's side) could pose a risk to your baby. If a family member has mental retardation, a genetic counselor can help you determine what, if any, risk there may be to your baby. This may involve obtaining records or even a physical exam of the affected person, and then genetic testing of you or the baby's father.

Sex-linked disorders: hemophilia is the most common example of a condition that is carried by females but only affects males. Any males in the family who have bleeding disorders should prompt a genetic consult in which the family tree can determine if you could have inherited the gene and are at risk of passing it on to a male fetus.

Autosomal dominant disorders: these are disorders in which there is a 50% chance of transmitting the gene to the fetus. An example is Marfan syndrome, in which a relative may be tall, have long fingers and toes, problems with eyesight, cardiac problems, and other findings. Autosomal dominant disorders can often be subtle in their manifestations.

Autosomal recessive disorders: these are conditions in which both parents must carry the abnormal gene in question in order for the fetus to inherit the condition. Usually, if a relative is affected with one of these conditions, it must be a first-degree relative (parent or sibling) for there to be a significant risk to your baby. Nonetheless, relatives who have conditions such as cystic fibrosis, Tay-Sachs disease, or beta-thalassemia must be noted so that the risk to your baby can be estimated. Several of the autosomal recessive disorders are considered for automatic testing of all pregnant women - see the chapter on screening for more information.