Genetic Testing

During pregnancy, you will have the option of testing for genetic diseases. Your provider may recommend additional testing based on your age, ethnicity, and reported personal or family history. Examples of these special tests are:

Chromosomal Screening Tests (for the fetus)

  1. California State Prenatal Screening Program (CPSP): The state screen provides pregnant women with a risk assessment for Down Syndrome (Trisomy 21), Edwards Syndrome (Trisomy 18), Smith-LemliOpitz Syndrome, and open neural tube defects. If you decide to proceed with this test, your blood will be drawn by our office during your visit (10 weeks – 13 weeks, 6 days) and again later in your pregnancy (15 – 20 weeks). You will also need to schedule a Nuchal Translucency Ultrasound at UCSF Radiology during your 12th week of pregnancy. These three components–1st-trimester blood draw, 2nd-trimester blood draw, and the Nuchal Translucency ultrasound–make up the California State Prenatal Screening Program. 
  2. Non-Invasive Prenatal Testing (NIPT): NIPT is a non-invasive blood draw that can detect common fetal chromosomal abnormalities, rare sex aneuploidies, and select microdeletions. This test provides a high degree of accuracy without the risks associated with more invasive procedures and can be done any time after 10 weeks. 

Usually, the CPSP and NIPT are done in combination to produce the most accurate screening assessment of the fetus currently available. 

Chromosomal Diagnostic Tests (for the fetus)

  • Chorionic Villus Sampling: 10 – 14 weeks
  • Amniocentesis: 16 – 20 weeks

Carrier Testing for Cystic Fibrosis

Cystic Fibrosis (CF) is one of the most common inherited diseases. About 1 in 3200 Caucasians in the United States have cystic fibrosis, which means 1 in 29 Caucasians are carriers of this condition. Although it is less common in people of other ethnic or racial backgrounds, you may still wish to consider carrier testing even if you are only part Caucasian or if your partner is not Caucasian.

Cystic Fibrosis affects the lungs and pancreas, requiring lifelong treatment or lung transplantation. Cystic Fibrosis does not affect intelligence. It is a genetic disease that is inherited from both parents as an autosomal recessive condition. This means a child has a chance of being afflicted if both parents are carriers. A carrier is someone who has only one gene with the CF mutation and one gene that is normal. Carriers are typically symptom-free and do not know that they carry the mutation. 

If no one in your family has cystic fibrosis, the chance that you are a carrier is based on your ethnic group: 

  • Caucasian: 1 in 29
  • Hispanic: 1 in 46
  • African-American: 1 in 65
  • Asian-American: 1 in 90

If you and your partner are both carriers of a cystic fibrosis gene mutation, there are tests available to determine whether the baby has the disease. This testing can be performed using cells from chorionic villus sampling (CVS) or amniocentesis. If both members of a couple are carriers of a cystic fibrosis gene, in each pregnancy there is a 25% chance of having a child with the disease and a 75% chance of having a child without the disease. 
Carrier testing for cystic fibrosis involves either a blood or saliva sample. Because the laboratory isolates DNA and tests for specific genetic mutations connected with specific diseases, the result is highly accurate. 

Expanded Carrier Testing

It is possible to test you and your partner for other diseases for which you could be carriers. Some of these diseases cause birth defects and/or shortened lifespan. Some can be treated if detected early. As a carrier, you are likely healthy and have no idea that you have an abnormality in your genes. However, if both you and your partner are a carrier of the same disease, there is a 25% risk with every pregnancy that the baby could inherit both parental gene mutations and possibly be affected. 

Thankfully there is only a 1% chance that both you and your partner are a carrier of the same disease but now is an opportunity to do carrier screening with a simple blood test to test for the possibility. If both you and your partner are carriers of the same disease, then there is genetic counseling and the option of diagnostic testing for the fetus. 

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