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Prenatal Screening and Diagnostics

  • Tests that can provide valuable information about a baby's health
  • Detects possible birth defects or genetic disorders
  • Different screening tests are performed at certain time points during the pregnancy
  • Involves Laboratory Medicine, High-Risk Pregnancy Program, and Prenatal Genetic Diagnosis Program

Prenatal Screening and Diagnostics


Pregnant and expecting mothers have the opportunity to learn a lot about their unborn child's health with today's genetic screening and diagnostic tests. Prenatal genetic testing allows the expectant mother and her health care team to provide the best health care for the baby. At Yale Medicine, prenatal screening and diagnostic tests are completed in a clinical chemistry lab. Scientists and researchers work with doctors caring for expecting mothers to help monitor pregnancies and ensure that mothers and their loved ones are identifying any possible challenges early. 

"One of the important distinctions to make is whether the test is for screening or diagnosis," says Yale Medicine's Katherine Harper Campbell, MD, MPH, medical director of the Yale Medicine's Maternal-Fetal Medicine section. A screening test allows the mother and her care team to know if a baby has a higher risk of developing a condition, Dr. Campbell explains. "A diagnostic test is more invasive and can convey a clear 'yes' or 'no' about a condition or disease a baby has," Dr. Campbell says. 

At Yale Medicine, a team of experts in diverse areas, including ultrasound, fetal care and genetic counseling, work together to provide the highest level of personalized care for all expectant mothers. 

What is prenatal screening?

By taking biochemical and ultrasound measurements, physicians can identify pregnancies at a serious risk of birth defects. With the results, healthcare providers can calculate specific risks of Down’s syndrome, a genetic disorder that can lead to mild to severe intellectual disability and occurs in about 1 in 700 infants. A test is also possible for Trisomy 18, a severe genetic disorder, as well as spinal birth defects.

Prenatal testing involves both screening tests and diagnostic tests. Screening tests are not diagnostic. They can provide information regarding the risk of a baby having a certain disorder or condition. Only diagnostic tests are definitive and can identify if a baby does have a birth defect.

What is the benefit of prenatal testing?

The tests can be especially helpful for pregnant women who are older, as the results can help them to decide whether to have further diagnostic testing relatively early in their pregnancies. Risk assessment includes not only blood test results and ultrasound measurements, but also incorporate factors such as age and ethnicity to determine risk of pregnancy abnormalities.

"We also recommend that expectant mothers undergo carrier screening for the status of any common recessive genetic diseases, including cystic fibrosis, spinal muscular atrophy and Fragile X syndrome," Dr. Campbell says. The best time for carrier screening is prior to conception or early in the pregnancy. 

What is a prenatal cell-free DNA (cfDNA) screening test?

This is a blood test that can determine the sex of the baby and provide information regarding the risk of a child having a chromosomal disorder. This test is recommended for women who are at least 10 weeks pregnant. "The biggest appeal of this test is that it can be done from a simple blood sample," Dr. Campbell says. 

Which tests are performed to determine potential birth defects?

The following are prenatal tests frequently performed at Yale Medicine. Speak with your doctor about potential false-positive results.

  • First-Trimester Screen (nuchal translucency, hCG, and PAPP-A): This test is usually performed during weeks 11-13 of pregnancy. It's a noninvasive evaluation combining a mother's blood screening with an ultrasound of the fetus. The test includes nuchal translucency, a portion that can help discover other potential abnormalities, including heart disorders. Primarily, the test is for chromosomal abnormalities, including Down syndrome or Trisomy-18.
  • Chorionic Villus Sampling (CVS): This test can be administered during weeks 10-13 of pregnancy. A sample of tissue is taken from the placenta and evaluated to identify chromosomal abnormalities and other inherited disorders, including Down syndrome and cystic fibrosis.
  • Second-Trimester Quad Screen (AFP, hCG, Estriol, Inhibin-A), Integrated Screens: This screen can be done during weeks 16-18 of pregnancy. This blood test measures levels of alpha-fetoprotein (AFP), a fetus-produced protein; human chorionic gonadotropin (hCG), a hormone made in the placenta; estriol, an estrogen formed by the mother and the placenta; and inhibin-A, a protein produced in the placenta and in the ovaries. It tests for Down syndrome, Trisomy-18, and other chromosomal abnormalities. It can also help evaluate the chance for neural tube defects, such as spina bifida, and abdominal wall defects, such as omphalocele.
  • Amniocentesis (also referred to as amniotic fluid test or AFT): This diagnostic test is performed during weeks 15-20 of pregnancy. A small amount of amniotic fluid is sampled from the amniotic sac that surrounds the fetus.

Who is first-trimester risk assessment for?

The first trimester lasts between weeks 1-12 and all pregnant women should consider screening tests during this time. Every baby has a tiny risk of having Down syndrome—even babies of two young parents.

What happens at a first-trimester risk assessment?

Noninvasive screening methods are used, including ultrasound and blood analysis. Blood is typically drawn before the patient’s appointment, so expecting mothers can receive results immediately.

The quad screen, also called the quadruple marker test or second-trimester screen, is recommended for women between 15 and 20 weeks of pregnancy to measure serum alpha-fetoprotein (AFP) and determine risk for open fetal spinal defect (or spina bifida).

What makes Yale Medicine's approach to prenatal screening unique?

Through our epidemiological monitoring program, we share data with obstetricians and physicians and work closely with them to track performance. We monitor trends in overall test results and review them with our clinicians every quarter to ensure that pregnant patients are receiving the best possible care, as well as the most up-to-date prenatal testing.