Type of testing for genetic disorders during pregnancy
There are many types of testing for genetic disorders during pregnancy. Your obstetrician will recommend the right one for you. Sometimes, more than one genetic test or screening is required for definite results. The earlier these prenatal tests are done the better prepared you can be for the future. It is important to note that not everyone who is asked to do a prenatal test or who has a positive result will have a baby with genetic or chromosomal abnormalities.
What is genetic disorder testing?
Genetic prenatal screening and testing determines whether your baby carries genes for certain disorders. The most common being Down syndrome, Spina bifida and Tay-Sachs, etc. While some tests have a high rate of accuracy they are not able to predict severity.
Reasons for genetic prenatal testing:
- You are pregnant and over the age of 35
- A family medical history of genetic or chromosomal abnormalities
- You already have a child (or children) with birth defects
- You have had two or more miscarriages
- You have delivered a stillborn baby with symptoms of genetic illness
- A previous test suggests your pregnancy is at high risk for a genetic disorder
What are the different types of testing for genetic disorders during pregnancy?
- Ultrasound: Also called a sonogram, it is non-invasive, relatively low risk and cost effective. This makes it an indispensable tool in monitoring pregnancy, especially when high risk. There are many different kinds:
- First trimester ultrasound: It determines the viability of a fetus when there is spotting during pregnancy, cramping in the first trimester or other irregularities.
- Level 2 ultrasound: A detailed, full fetal anatomy scan with sophisticated imaging for detection of abnormalities.
- Amniocentesis: This diagnostic prenatal test can help you identify inherited diseases like Tay-Sachs, chromosomal abnormalities like Down syndrome and open neural tube defects such as Spina bifida. It is recommended approximately between 15 to 23 weeks of your pregnancy.
- First trimester screening: A non-invasive screening option combining a maternal blood screening test with an ultrasound evaluation of the fetus to identify risk for specific chromosomal abnormalities, including Down syndrome, Trisomy-21 and Trisomy-18.
- Integrated screening: This prenatal testing procedure combines measurements from a nuchal translucency ultrasound and two blood tests. Unlike your first trimester assessment, it will also determine if there is an increased chance of Spina bifida.
- Sequential Screening: This form of prenatal testing offers a way to estimate if your baby will be born with chromosomal abnormalities like Down syndrome, Trisomy 18, as well as open neural tube defects. Two blood tests measure proteins that are made by the developing baby and placenta. The first blood test is taken between the 11th and 13th week of your pregnancy. The second blood test is taken ideally between 15 and 18 weeks, although it can be done up to the 21st week. An ultrasound is performed between the 11th and 13th week, to confirm the right timeframe for the screening. This also includes the nuchal translucency.
- Maternal serum screens: It uses blood taken at 15 to 20 weeks of pregnancy to screen for Down syndrome and Trisomy 18 for women who have NOT had first trimester screening or integrated prenatal screening. Approximately 85% of pregnancies with Down syndrome and 60% of pregnancies with the chromosome abnormality Trisomy 18 are identified as screen positive with this blood test.
- Blood tests: There are a couple of blood tests (like the one above) that can help determine your risks. A multiple marker screening may be recommended to determine your baby's risk of certain chromosomal abnormalities (like Down syndrome and trisomy 18) and neural tube defects (such as Spina bifida). This is done in the second trimester, between 16 and 20 weeks. An AFP blood test is normally done as part of the multiple marker screening. This test screens for a protein called alpha-fetoprotein in order to detect the possibility of neural tube defects. It's possible to have an AFP blood test if you have had first-trimester combined screening and are not having a multiple marker screening.
- Non-Invasive Prenatal Testing (NIPT): A new option in the prenatal screening and testing for trisomy 21 and a few other fetal chromosomal abnormalities using cell-free fetal DNA. Testing is typically done between 10-22 weeks. Results can take a week or more.
Genetic counseling helps understand your options and your risks. All types of testing for genetic disorders during pregnancy is voluntary.
Dr. Jorge L. Gomez earned his Medical Degree in 1990 at Central Del Caribe University in Bayamon, Puerto Rico. Following residency in Obstetrics and Gynecology at Bronx-Lebanon Hospital center in the Bronx, NY (1990–1994), he completed additional fellowship training at New York University Medical Center NY, specializing in Maternal Fetal Medicine (1994-1996). After his fellowship in 1996 he joined South Florida Perinatal Medicine. Dr. Gomez is Board certified in OBGYN and Maternal Fetal Medicine. From 2003–2007 He was a reviewer for the American Journal Of Obstetrics and Gynecology.