The Different Types of Prenatal Screening Tests: Part 2, Blood Screens

Prenatal screening can be an important part of prenatal care. It can help detect specific health conditions in babies before birth. Your healthcare provider may recommend several screening tests during your pregnancy, each of which can help provide important information about your baby's health. Learn more about the different types of prenatal screening tests available and what they can offer expectant parents here.

Non-invasive prenatal screening tests

Non-invasive prenatal screening tests are blood tests that a pregnant person can take to check the pregnancy for certain chromosomal conditions, such as trisomy 21, 18, and 13. Non-invasive prenatal screening (NIPS), also called non-invasive prenatal testing (NIPT), can be performed as early as 9 weeks gestation, and unlike other prenatal blood screens, they generally do not have a maximum gestational age. NIPS or NIPT typically involves a simple blood collection from the pregnant person, and there’s no associated risk to the pregnancy. Results from NIPS/NIPT usually are available within one to two weeks, and will indicate whether there is an increased chance of certain chromosome conditions in the pregnancy.

The American College of OB/GYNs recommends that all pregnant patients have the option to undergo NIPS/NIPT. Although this screening is not diagnostic, and it’s possible to have false positive or false negative results, research in pregnancies of all risks has demonstrated NIPS to be more accurate than other prenatal blood screens.

Combined first-trimester screening

Combined first-trimester screening has two essential components: the nuchal translucency (NT) sonogram at 11w0d-13w6d, and a maternal blood sample collection performed within this same window. Data from the NT sonogram and the blood sample are analyzed to provide an adjusted risk for Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18); sometimes, a combined risk for Edwards syndrome and Patau syndrome (trisomy 13) will be provided. Since both the NT sonogram and the maternal blood sample collection are technically non-invasive, there are no linked risks for pregnancy loss from combined first-trimester screening. While this screening does not perform as well as NIPS/NIPT for identifying certain chromosome conditions, it may be a good option for parents whose insurance does not cover NIPS/NIPT without a “high risk” indication.

Serum integrated screening

Serum integrated screening, or integrated screening for short, analyzes chemicals from a first-trimester maternal blood sample and a second-trimester maternal blood sample. It provides an adjusted risk for Down syndrome, trisomy 18, and spina bifida once both blood samples have been collected and analyzed. Since serum integrated screening does not involve an ultrasound, it may be preferred by your prenatal care provider if an NT-certified sonographer is not available in your area. Still, the performance of NIPS/NIPT for detecting fetal chromosome conditions is much higher than that of serum integrated screening, and NIPS/NIPT also does not require a prenatal ultrasound to be performed.

Quad screening (Quad Marker Test)

Another type of prenatal screening test is the quad screen, or quadruple screen test, which may be offered during the second trimester of pregnancy. This blood test checks for specific hormones produced by the baby and the placenta and can indicate a higher chance of certain congenital conditions, such as Down syndrome. The quad screen is typically done between 16 and 18 weeks of pregnancy, and results tend to be available within one to two weeks.

Prenatal screening tests vs. prenatal diagnostic tests

Amniocentesis and chorionic villus sampling (CVS) are two types of prenatal screening tests that analyze samples directly from the pregnancy – an amniotic fluid sample for amniocentesis and tiny pieces of placental tissue for CVS. A trained physician (usually a high-risk OB/GYN called a Maternal Fetal Medicine specialist) performs amniocentesis by inserting a needle into the uterus to collect a few tablespoons of amniotic fluid containing genetic material from the baby’s cells. Amniocentesis is performed under ultrasound guidance so that the physician is able to collect the amniotic fluid sample from the largest fluid pocket, as far away from the baby as possible. This procedure is usually only performed after around 16 weeks gestation, when the membranous layers of the gestational sac have fused together. In contrast, an MFM specialist usually performs a CVS procedure between 10 to 14 weeks gestation and does this by taking a very small placenta biopsy.

This biopsy can be completed either through a transabdominal approach or a transvaginal approach, depending on factors such as the location of the placenta’s attachment to the uterus. Although both the amniocentesis and CVS procedures are considered safe when performed by an experienced provider, these procedures do carry some risks for pregnancy loss, such as if the bag of water were to break or infection were to occur after the procedure. It’s always important to talk to your provider about the risks and benefits of prenatal diagnostic procedures like amniocentesis and CVS so you can make an informed choice.

Some parents choose to begin their prenatal screening and testing journey with non-invasive prenatal screening tests, such as NIPS, knowing they can follow up with prenatal diagnostic testing if NIPS reveals an abnormal or high-risk result. In other instances, parents may prefer to schedule prenatal diagnostics testing as their first-tier approach for gathering health information about their baby. If you’re not sure what approach is right for you, you might benefit from consulting with a genetic counselor about your pregnancy and family history, any other risk factors you perceive, and each of your options for prenatal screening and testing.

Read more about the benefits and limitations of non-invasive prenatal screening tests.

Please note: JunoDx.com and the materials and information it contains are not intended to, and do not constitute medical or other health advice or diagnosis and should not be used as such. You should always consult with a qualified physician or health professional about your specific circumstances.