Prenatal diagnosis The Genetics Center, Inc.

The Genetics Center, Inc. Address, phone, and fax

Genetics and Prenatal Diagnosis:

Some straightforward answers to
common questions

Prenatal diagnosis is available for many genetic conditions, and a growing number of women are seeking advice regarding prenatal testing for a present or planned pregnancy. In most cases, a genetics consultation is important for both the patient and physician.

What can be prenatally diagnosed?
Chromosome abnormalities:

Down syndrome and other chromosome abnormalities increase in frequency as the age of the mother increases. Women who will be 35 years or older at the time of delivery are candidates for prenatal chromosome diagnosis.
In women under 35, abnormal results of maternal serum screening may indicate an increased risk for Down syndrome.
Other individuals with family histories of chromosome abnormalities, or with family histories which may raise a suspicion of chromosome abnormalities, may benefit from prenatal diagnosis.

Metabolic diseases:

Many metabolic diseases, such as Tay Sachs disease and PKU, can be diagnosed prenatally. The need for such prenatal diagnosis must be established prior to performing the amniocentesis so that the proper testing can be ordered and accomplished in a timely manner.

Spina bifida and other birth defects:

Measurement of alpha-fetoprotein allows detection of most cases of spina bifida and several other birth defects.

Other genetic diseases:

Cystic fibrosis, neurofibromatosis, Huntington disease, beta-thalassemia, hemophilia, Duchenne muscular dystrophy, and a variety of other diseases can be detected prenatally under certain circumstances. Genetic evaluation is essential in selecting the appropriate tests to perform and identifying additional individuals in the family who may require testing. It is best to consider these issues before a pregnancy, since genetic testing sometimes takes a considerable amount of time.

Who benefits from a genetic consultation?
The referring physician:

Because the geneticist can identify all genetic risk factors and suggest appropriate testing, the referring physician can be confident that all medically indicated testing will be offered to the patient and that unnecessary testing is avoided.

The patient and family:

The geneticist discusses genetic risk factors and any medically indicated genetic testing, allotting sufficient time for questions. Risks of prenatal testing and details about the prenatal diagnosis procedures are thoroughly discussed. Having all of this information allows prospective parents to make a truly informed decision about genetic testing and/or prenatal diagnosis.

Who decides about obtaining a genetic consultation?

The decision to make a referral for a genetics specialist is based on medical and family information. Patients may also request that their physician refer them for genetics consultation.

The genetic consultation consists of obtaining a detailed family history, identifying any factors occurring during a pregnancy that may increase the risk that the fetus will have a birth defect, determining appropriate prenatal testing, and explaining the risks and benefits of the suggested prenatal testing.

What if a previous genetic evaluation has been done?

Genetics is one of the most rapidly changing fields of medicine. It is possible that information obtained only a year ago may already be out of date. Review consultations can be scheduled prior to, or on the same day, as an amniocentesis.

Why "bother" with genetic consultation at all?

It is a personal decision to pursue prenatal diagnosis and genetic evaluation. However, for a prenatal diagnostic procedure that involves a small risk to a fetus or mother, a truly informed decision is important. Therefore, a genetic consultation is important prior to any prenatal diagnosis procedure other than those which would not put the fetus at risk (such as ultrasound or maternal blood testing).
Medical genetics today is such a highly specialized field that few non-geneticists can claim sufficient expertise to provide a thorough prenatal genetic evaluation and answer relevant genetics questions.