Prenatal Testing: Common Tests, Why They're Performed & What They Tell Us in Pregnancy

NIPT/Non-invasive Prenatal Testing: 

MaterniT 21 PLUS screens for certain chromosomal abnormalities called trisomies, including trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome).

But it digs deeper, screening for certain sex chromosome aneuploidies (SCAs, abnormal numbers of X or Y chromosomes) and select microdeletions (missing parts of chromosomes).

We are not just checking to see the gender of your baby, the testing is more detailed vs just gender.

Nuchal Translucency:

Nuchal translucency (NT) is the sonographic appearance of a collection of fluid under the skin behind the fetal neck in the first-trimester of pregnancy. The term translucency is used, irrespective of whether it is septated or not and whether it is confined to the neck or envelopes the whole fetus. In fetuses with chromosomal abnormalities, cardiac defects and many genetic syndromes the NT thickness is increased.

Screening by NT can detect about 80% of fetuses with trisomy 21 and other major aneuploides for a false positive rate of 5%. The combination of NT and maternal serum free β-hCG and PAPP-A improves the detection to 90%. There is now evidence that the detection rate can increase to about 95% and the false positive rate can be reduced to 3% by also examining the nasal bone, ductus venosus flow and tricuspid flow.

AFP(alpha-fetoprotein)/Quad Screening:

The alpha-fetoprotein (AFP) test is a blood test for pregnant people. Healthcare providers use the AFP test to check a fetus’s risks of birth defects or genetic conditions.

The AFP test measures alpha-fetoprotein levels. Alpha-fetoprotein is a protein that develops in the liver of a fetus. Irregular AFP levels in pregnant people can be a sign of a genetic disorder or birth defect (congenital disability).

Anatomy Ultrasound:

A 20-week ultrasound takes measurements of your fetal organs and body parts to make sure the fetus is growing appropriately. The scan also looks for signs of specific congenital disabilities or structural issues with certain organs.

Some specific parts your provider will examine are the fetal:

• Heart.
• Brain, neck and spine.
• Kidneys and bladder.
• Arms and legs.
• Hands, fingers, feet and toes.
• Lips, chin, nose, eyes and face.
• Chest and lungs.
• Stomach and intestines.

The ultrasound technician will also:

• Listen to the fetal heart rate for abnormal rhythms.
• Check the umbilical cord for blood flow and where it attaches to the placenta.
• Look at the placenta to make sure it’s not covering your cervix (placenta previa).
• Check your uterus, ovaries and cervix.
• Measure the amount of amniotic fluid.

Glucose Challenge Test:

Gestational diabetes

The American College of Obstetricians and Gynecologists recommends performing a one-hour blood glucose challenge test to screen for gestational diabetes in low-risk pregnant women between 24 and 28 weeks of pregnancy.

Your provider may recommend earlier screening if you're at increased risk of developing gestational diabetes. Risk factors may include:

• Gestational diabetes in an earlier pregnancy
• Family history of diabetes
• Obesity
• Having a medical condition associated with the development of diabetes, such as metabolic syndrome or polycystic ovary syndrome

If your provider determines you're at risk or you have a suspicious value on the one-hour test, you may be advised to take a three-hour glucose tolerance test.

Group Beta-Strep Test:

According to ACOG, GBS most often is found in the vagina and rectum. This means that GBS can pass from a pregnant woman to her fetus during labor. This is rare and happens to 1 or 2 babies out of 100 when the mother does not receive treatment with antibiotics during labor. The chance of a newborn getting sick is much lower when the mother receives treatment.  

Pregnant women are screened for GBS as part of routine prenatal care. The test for GBS is called a culture. It is now done between 36 and 38 weeks of pregnancy. In this test, a swab is used to take a sample from the vagina and rectum.

If the results show that GBS is present, most women will receive antibiotics through an intravenous (IV) line once labor has started. This is done to help protect the fetus from being infected. The best time for treatment is during labor. Penicillin is the antibiotic that is most often given to prevent early-onset disease in newborns. While treatment with antibiotics during labor can help prevent early-onset GBS disease in a baby, this treatment does not prevent late-onset disease.

STD testing: First and Third Trimester

STDs can complicate pregnancy and may have serious consequences for both a woman and her developing baby. As a healthcare provider caring for pregnant women, we have a key role in safeguarding the health of both a mother and her unborn child.

A critical component of appropriate prenatal care is ensuring that pregnant patients are tested for STDs starting early in their pregnancy and repeat close to delivery. To ensure that the correct tests are being performed, we encourage you to have open, honest conversations with your providers about symptoms you have experienced or are currently experiencing and any high-risk sexual behaviors in which you engage.

LIST of STIs:

• HIV, Syphillis, Hepatitis B, Chlamydia, Gonorrhea, Trichomonas, HSV 2
• Including other infections: Bacterial Vaginosis, ureaplasma

References:

https://www.labcorp.com/pregnancy/maternit21-plus

https://fetalmedicine.org/fmf-certification-2/nuchal-translucency-scan

https://my.clevelandclinic.org/health/diagnostics/24301-alpha-fetoprotein-test

https://my.clevelandclinic.org/health/diagnostics/22644-20-week-ultrasound

https://www.mayoclinic.org/tests-procedures/glucose-tolerance-test/about/pac-20394296

https://www.acog.org/womens-health/faqs/group-b-strep-and-pregnancy

https://www.cdc.gov/std/pregnancy/stdfact-pregnancy-detailed.htm