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How Does Genetic Screening Work?

Obstetrics & Gynecology located in Amarillo, TX

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Prenatal genetic screening is optional, noninvasive testing that provides information about your fetus’s risk of having certain genetic disorders. Learn how it works and what it can (and can’t) reveal about your developing baby’s health.

Pregnancy is a time of joyful expectation for many women. But in some cases, it can be a time of unsettling anxiety too. You may find yourself wondering and worrying about your unborn baby’s health, particularly if you’re older than 35 or have a family history of genetic disorders.

While most babies are born healthy, it’s important to understand your prenatal genetic screening options, including how the process works and what kind of details it can (and can’t) reveal about your baby’s health. 

Here, our seasoned team of board-certified obstetrics experts at Panhandle Obstetrics and Gynecology in Amarillo, Texas, offers further insight into the optional process of prenatal genetic screening and the information it provides.

What is prenatal genetic screening?

Prenatal genetic screening refers to a set of noninvasive tests that give you information about whether your developing baby has a higher risk of certain genetic disorders compared to the general population.

Genetic disorders develop when a harmful change to a gene called a pathogenic variant, or mutation, affects a person’s genetic quality or quantity. Genetic disorders can be:


These genetic mutations affect the structures (chromosomes) that hold DNA within each cell. The appearance of an extra, duplicated chromosome is a genetic disorder known as trisomy; a missing chromosome is called monosomy. Trisomy 21, or Down syndrome, is one of the most common chromosomal genetic disorders. 

Single gene

Monogenic disorders are caused by a single gene mutation inherited from just one parent. These disorders are typically recognized by their striking familial inheritance patterns. Cystic fibrosis and sickle cell disease are examples of single-gene genetic disorders. 


Multifactorial genetic disorders arise from a combination of gene mutations present at birth and gene-affecting environmental, circumstantial, and lifestyle factors. 

Many chronic illnesses (i.e., heart disease, type 2 diabetes, Alzheimer’s disease) and mental health disorders (i.e., depression, schizophrenia) are known to cluster in families and have a genetic component. Because they don’t have a clear-cut pattern of inheritance, however, they’re considered complex, multifactorial genetic disorders. 

How does genetic screening work?

To determine whether your baby is more or less likely to inherit certain gene-related birth defects, prenatal screening tests use four basic techniques:

  • Carrier testing
  • Blood testing
  • Ultrasound imaging
  • Cell-free DNA screening

Using a blood sample or cheek swab, carrier testing can determine whether you or your partner carries any gene mutations for monogenic (single gene) disorders. You can opt to have carrier testing any time before or during pregnancy. 

Prenatal genetic screening tests, which include blood tests, ultrasound imaging, and cell-free DNA screening, are offered in the first two trimesters of pregnancy. 

First trimester 

Offered between weeks 11-14 of gestation in the first trimester, early genetic screening uses a blood test to check for two specific substances, along with a specific type of ultrasound exam called a nuchal translucency screening, which measures the amount of fluid behind your baby’s neck.

The combined information from the blood test and ultrasound exam assesses the risk level of common chromosomal disorders like Down syndrome. 

As early as 10 weeks of gestation, you can opt to have a cell-free fetal DNA screening. This noninvasive test checks a sample of your blood for fetal DNA, specifically looking for signs of chromosomal conditions like Down syndrome, trisomy 13, and trisomy 18. 

Second trimester 

Offered between weeks 15-22 of gestation, second-trimester genetic screening includes another maternal blood test and a second ultrasound. 

The blood test — known as the “quad” screen — measures the levels of four proteins made by a developing fetus: alpha-fetoprotein (AFP), unconjugated estriol (UE), human chorionic gonadotropin (hCG), and inhibin-A. Abnormal (high or low) levels can indicate an increased risk of chromosomal disorders or neural tube defects (NTDs) that cause abnormal brain and spine development. 

A second fetal ultrasound exam (done between weeks 18-22 of pregnancy) checks for major physical defects in the brain and spine, abdomen, heart, facial features, and limbs. 

Should I consider genetic screening?

Opting for prenatal genetic testing is a personal choice. While results within the normal range may ease your anxieties, abnormal results might lead to a heart-wrenching decision. 

But it’s very important to recognize that prenatal genetic screening is a risk assessment, not a diagnosis — it doesn’t tell you for sure that your developing fetus has a genetic condition. 

If screening results indicate an elevated risk for a genetic disorder, you can choose to undergo prenatal diagnostic genetic testing, such as amniocentesis or chorionic villus sampling (CVS), for more conclusive results. Some of the main reasons families opt for diagnostic genetic testing during pregnancy are:

  • Family or personal history of genetic disorders
  • Pregnancy occurring after the age of 35
  • A history of recurrent miscarriage or stillbirth

To learn more about the prenatal genetic screening options available at Panhandle Obstetrics and Gynecology, or to schedule an appointment at our office, give us a call at 806-359-5468 today.