Your Definitive Guide to Prenatal Testing

The prenatal period is the time before your baby is born, an important time in fetal growth and development. Prenatal tests and screenings are essential in ensuring both your own health and the health of your baby. There are many screening tests recommended by the American College of Obstetricians and Gynecologists, so let’s dig in!

At this point, you’ve probably peed on a stick and gotten a positive result on a home pregnancy test. That means your body has begun producing a level of a hormone called Human Chorionic Gonadotropin that is detectable in your urine. Human Chorionic Gonadotropic (or beta-hCG) is produced in response to the placenta implanting in the uterus. Home pregnancy tests are considered qualitative beta-hCG tests. That is, they tell you whether or not there is a detectable level of the hormone in your urine. Your doctor will want to do an additional test, a blood test called a quantitative beta-hCG test, to measure exactly how much of the hormone is being produced. Too much beta-hCG could indicate a problem that would require further investigation.

You will also get a bunch of other blood tests. First is a CBC, or a complete blood count, to check for anemia or any other blood abnormalities. Then your blood type will be determined as well as your Rh factor. Most people are Rh positive. If you’re found to be Rh negative (and the baby’s father is Rh positive), you will be easily treated to make sure your baby doesn’t develop hemolytic anemia. Your blood will also be tested for antibodies against rubella (German measles) and varicella (chicken pox). If you don’t have antibodies that means you’re not immune to these diseases and are at risk of contracting either of the illnesses. You should exercise extra caution around—or completely avoid—anyone who has chicken pox or German measles.

Further blood tests include screening for sexually transmitted infections like chlamydia, gonorrhea, syphilis, and HIV. You will also be screened for hepatitis B. If you are determined to be at risk, additional screenings include hepatitis C, herpes, toxoplasmosis, and Zika virus. You may also need a vaginal swab to test for trichomonas vaginalis.

But wait, like a late-night infomercial, there’s more! Your doctor will most likely want to do a Pap test as well. And she or he won’t let you leave the office without having you pee in a cup to make sure there’s no bacteria in your urine. Even if you have no symptoms of a urinary tract infection, that bacteria can harm your developing baby. A simple course of antibiotics can wipe out the infection.

Additionally, you may choose to do some optional genetic testing. Your doctor may offer a carrier screen for cystic fibrosis (CF) and/or spinal muscular atrophy. These are tests done on your blood, saliva, or a scraping from the inside of your cheek to determine if you are a genetic carrier of these diseases. If you are found to be a carrier, your partner should also be tested to determine your baby’s risk. This can be done before or any time during your pregnancy.

Another optional genetic screen can be done after 10 weeks. Noninvasive prenatal testing (NIPT), sometimes referred to as noninvasive prenatal screening (NIPS), can analyze fragments of your baby’s DNA from a sample of your blood. This test can screen for missing or extra chromosomes, or aneuploidy. Specifically, NIPT looks for trisomy 21 (also known as Down Syndrome), trisomy 18, trisomy 13, and any extra or missing X or Y chromosomes. At that time, if an abnormality is detected, a chorionic villus sampling (at 10 to 13 weeks) or an amniocentesis (at 14 to 20 weeks) can be performed to test the fetal tissue directly. These two tests can also detect cystic fibrosis.

Between the 11th and 14th weeks of pregnancy, if you’ve opted out of NIPT, a nuchal translucency screening can be done on ultrasound. In this screening, the thickness of the back of the baby’s neck is measured on the sonographic image. Increased thickening could indicate Down Syndrome or heart issues.

You should have a maternal serum screen at about 15 to 20 weeks to look for chromosomal abnormalities and neural tube defects like spina bifida. This test is also called a triple test, a quad screen, or an AFP.

Gestational diabetes is a concern around 24 to 28 weeks into your pregnancy. You will be given a glucose challenge, which consists of drinking a syrupy drink and having a blood test about an hour later to determine your risk of developing gestational diabetes. Based on your resulting blood sugar level, you may be given a glucose tolerance test (or GTT). The GTT involves a fasting blood sugar test, followed by ingestion of a sugary beverage and subsequent blood sugar level testing every few hours after that. If you’re diagnosed with gestational diabetes, you may be treated with insulin.

After 28 weeks is when the non-stress test comes in. This test consists of measuring the baby’s heart rate to determine whether he or she is getting enough oxygen.

Finally, at around 35 or 36 weeks, your doctor will perform a vaginal and rectal swab to test for group B streptococcus. Although harmless to you, group B strep can cause pneumonia or other infections in your newborn. If you are positive for group B strep, you will be given antibiotics during labor to prevent vertical transmission to your baby.

The next test you will be given is whether or not you can function with little or no sleep for the next few years. Welcome to parenthood!

Janette DeFelice
Dr. Janette DeFelice is a writer currently focusing on how the changing environment affects our health. She holds a Doctor of Medicine degree from Chicago Medical School where she taught clinical and diagnostic skills to beginning medical students, and a Master’s degree in Humanities from the University of Chicago. She also has a Bachelor’s degree in Political Science. Her writing can be seen online at BeTheChangeMom, ChicagoNow, and Medium, and she’s very excited to have published her first novel, Delia Rising: A Ballet in Three Acts. She lives in Chicago’s west suburbs with her school-age twins, her husband, and a family cat named Clara Barton.

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