Prenatal Testing & Screening
First Things First: Tests to Confirm that You’re Pregnant
All pregnancy tests work by detecting a hormone in your blood or urine that’s there only if you’re pregnant. This hormone – human chorionic gonadotropin (hCG) – is produced when a fertilized egg implants in your uterus.
There are two types of pregnancy tests:
- A urine test can be performed at your doctor’s office or with a home pregnancy test
- Urine tests can usually tell if you’re pregnant about one week after a missed period
- A blood test checks your blood for hCG, and you need to see a doctor to have this test
- Blood tests can detect hCG earlier in a pregnancy than urine tests, usually 6 to 8 days after you ovulate
If a home pregnancy test shows that you’re pregnant, call your doctor right away. He or she can use a more sensitive test along with a pelvic exam to confirm it. Plus, seeing your doctor early in your pregnancy helps you and your baby stay as healthy as possible (visit our Prenatal Care & Delivery page to learn more about care during pregnancy).
Routine Tests During Pregnancy
Certain laboratory tests are recommended for all women as part of routine prenatal care. These tests can help detect conditions that might put you or your fetus at risk of complications, and allow for timely treatment.
Tests Done in Early Pregnancy
- Complete Blood Count (CBC) with Differential/Platelet – Measures the numbers of different types of cells that make up your blood to check for anemia, infection and your blood-clotting ability
- Urinalysis and Urine Culture – Detects urinary tract disease, infection, glucose (high levels may be a sign of diabetes) and protein.
- Hepatitis B – Pregnant women with Hepatitis B virus (which infects the liver) can pass the virus to their babies
- Rubella (German Measles) – Can cause birth defects if a woman is infected during pregnancy. Your blood is tested to see if you’ve had a past rubella infection or if you’ve been vaccinated against it.
- HIV – Pregnant women infected with HIV can be given medication and take other steps that greatly reduce the chance of passing the virus to their babies
- Varicella Zoster V Antibodies (Chicken Pox) – This test is done to detect whether a women is immune to varicella (chicken pox).
- Blood Typing – Determines your blood type and Rh factor (a protein on the surface of red blood cells). Blood types are either A, B, AB or O, and the Rh factor is either positive or negative.Problems can occur if a woman is Rh negative and her baby is Rh positive.
- Antibody Screen – If you are Rh negative, your immune system can develop an antibody that attaches to the Rh-positive antigens on your fetus’ red blood cells, targeting them for destruction. An antibody screen is used to detect these antibodies. The first Rh-positive baby is unlikely to become ill, but antibodies produced during a first pregnancy will affect future Rh-positive babies
- Sexually Transmitted Disease (STD) Testing – Pregnant women are screened for syphilis (a test called rapid plasma reagin, or RPR) and chlamydia early in pregnancy because these STDs can be passed to their babies and cause other complications.
- Thyroid Stimulating Hormone (TSH) – Because thyroid problems are associated with pregnancy complications, women are tested to ensure that their thyroid is functioning properly. This is tested in patients with specific family or medical history.
Tests Done Mid-Pregnancy
- Glucose Tolerance Test – This measures the level of glucose (sugar) in your blood; a high level may be a sign of gestational diabetes
- Hemoglobin and Hematocrit – It’s not uncommon to develop anemia as your pregnancy progresses, so your blood will be tested in your late second trimester or early third trimester
- RPR (Syphilis screen #2) – All women receive a second test to screen for syphilis in their second trimester
Tests Done in Late Pregnancy
- Group B Strep (GBS) Culture – GBS is a type of bacteria that lives in the vagina and rectum. Many women carry GBS without having symptoms, but it can be passed to a baby during birth and cause serious health problems. Antibiotics can be given during labor to help prevent infection of the baby.
Tests to Screen for Birth Defects
Today there are several noninvasive screening tests available to you in the first and second trimesters of pregnancy to assess the chances that your fetus may have a genetic (inherited) disorder and/or birth defects. If you are at risk, your doctor will discuss these optional tests with you.
- Sequential Screen – A two-stage screening that assesses the risk of several chromosomal abnormalities including Down syndrome. The first stage (combining ultrasound and blood testing) can be performed between 11 weeks and 13 weeks and 6 days. The second stage (blood testing) can be performed between 15 and 22 weeks.
- Maternal Serum Quad Screen– A maternal blood screening test that looks for four specific substances in the blood
- Alpha Fetoprotein (AFP) – This blood test checks the level of AFP in a pregnant woman’s blood during the second trimester
- Carrier Screening – Testing that’s done to see if you or your partner carry a genetic mutation that could cause a serious inherited disorder (such as cystic fibrosis) in your baby
- Non-invasive prenatal testing (NIPT) – Also called cell free DNA testing (cfDNA), this blood test analyzes fetal DNA circulating in a pregnant woman’s blood; it can be performed at 10 weeks. The American Congress of Ob/Gyn does not recommend NIPT in pregnancies when there is more than one fetus (twins, triplets, etc…).
It’s important to understand that these screening tests do not diagnose a problem; they only signal that further testing (such as amniocentesis or chorionic villus sampling) should be done.
Because many of these tests are done in women who are at high risk for having a child with a chromosomal abnormality or birth defect, we often recommend that they undergo genetic counseling to understand their options.
Questions about Prenatal Testing and Screening?
The physicians and nurses at WOMEN’S HEALTH of Central Massachusetts are here to provide answers. Simply contact us.