Alpha-fetoprotein (AFP): A protein made by the fetus. In women carrying a fetus with spina bifida and certain other conditions, levels in the mother's blood tend to be a little higher. In women carrying a fetus with Down syndrome, levels in the maternal blood tend to be a little lower.

Canavan disease: A severe, progressive disease of the brain that is usually fatal in childhood. It is an autosomal recessive genetic disease.

Genetic syndrome: A medical condition that is caused by changes in an individual's genes (their DNA). It may be passed down through a family or occur for the first time in one individual. Some genetic syndromes are very severe and some are fairly mild.

Hemoglobinopathies: A group of inherited disorders affecting red blood cells that can result in severe anemia and often other problems. Treatment may involve blood transfusions. Examples are sickle cell disease and thalassemia.

Hydrocephalus: An often serious condition where fluid builds up in the brain. It is sometimes detected prenatally by ultrasound and may be caused by genetic problems.

Spina bifida: An opening in the spine allows the spinal cord to be exposed andoften resulting in varying degrees of physical disability. Surgical repair is needed after birth. The use of a daily multivitamin with folate prior to conception reduces the chance for this condition to develop.

Tay-Sachs disease: A very severe, progressive disease of the brain that results in death in early childhood. It is an autosomal recessive disease so both parents must be carriers in order to have an affected child.

Ultrasound: A technique that uses high frequency sound waves to image the fetal anatomy.