GUIDE
You will have blood drawn several times during pregnancy to check blood type, Rh factor, complete blood count, infections, immunity, and more.
Most blood work is done at your first prenatal visit, with additional tests at 24-28 weeks and in the third trimester. Understanding what each test checks — and why — makes the process less stressful and helps you ask the right questions.
Be prepared from day one
Your first prenatal visit involves the most extensive blood draw of your pregnancy. Multiple vials will be collected to run a comprehensive panel of tests. This is standard and expected — the tests establish your baseline health status and screen for conditions that could affect your pregnancy.
These tests are recommended by ACOG, the CDC, and the U.S. Preventive Services Task Force for all pregnant people, regardless of age, health history, or risk level. They are not optional add-ons — they are the standard of care.
| Test | When | What It Checks |
|---|---|---|
| Blood type and Rh factor | First visit | Determines your blood type (A, B, AB, O) and Rh status. Rh-negative mothers need RhoGAM to prevent antibody issues. |
| Complete blood count (CBC) | First visit | Checks red blood cells, white blood cells, hemoglobin, hematocrit, and platelets. Screens for anemia and infection. |
| Rubella immunity | First visit | Confirms you are immune to rubella (German measles). If not immune, you will be vaccinated postpartum — the vaccine cannot be given during pregnancy. |
| Hepatitis B surface antigen | First visit | Screens for active hepatitis B infection. If positive, your baby will receive treatment at birth to prevent transmission. |
| HIV screening | First visit | Recommended for all pregnant people by ACOG and CDC. Early detection allows treatment to reduce transmission risk to near zero. |
| Syphilis (RPR/VDRL) | First visit | Screens for syphilis, which can cause serious complications if untreated. Treatable with antibiotics during pregnancy. |
| Chlamydia and gonorrhea | First visit | Urine or swab test. Both are treatable with antibiotics and can cause complications if undetected. |
| Urinalysis and urine culture | First visit | Screens for urinary tract infections and asymptomatic bacteriuria, which can lead to kidney infections if untreated. |
| Varicella (chickenpox) immunity | First visit | Confirms immunity. Chickenpox during pregnancy can cause serious complications. Vaccine given postpartum if not immune. |
About 15 percent of people are Rh-negative. If you are Rh-negative and your baby is Rh-positive (which depends on the father's Rh status), your immune system could develop antibodies against the baby's red blood cells. This is called Rh sensitization and can cause serious problems in future pregnancies.
The solution is simple and highly effective: a RhoGAM (Rh immunoglobulin) injection at 28 weeks, and another within 72 hours after delivery if the baby is confirmed Rh-positive. RhoGAM is also given after any event that could cause fetal-maternal blood mixing, such as amniocentesis, bleeding, or trauma.
If you are Rh-positive, this does not apply to you at all.
| Test | When | What It Checks |
|---|---|---|
| NIPT (cell-free DNA screening) | Weeks 10–13 | Screens for trisomies 21, 18, 13 and sex chromosome conditions. Optional but recommended by ACOG for all pregnancies. |
| First-trimester screening blood work | Weeks 10–13 | PAPP-A and free beta-hCG measured alongside the nuchal translucency scan for combined screening. |
| Carrier screening | Any time | Tests whether you carry genes for cystic fibrosis, sickle cell disease, spinal muscular atrophy, and other conditions. Ideally done before or early in pregnancy. |
| Thyroid function (TSH) | First visit | Not universal but often ordered. Thyroid disorders are common and can affect pregnancy outcomes if untreated. |
Carrier screening tests whether you carry a gene variant for conditions like cystic fibrosis, sickle cell disease, spinal muscular atrophy, fragile X syndrome, and others. Carriers are healthy — they have one working copy of the gene — but if both parents carry a variant for the same condition, each pregnancy has a 25 percent chance of being affected.
ACOG recommends that carrier screening be offered to all pregnant people (or ideally before pregnancy). Expanded carrier panels now test for over 100 conditions with a single blood draw. If you are found to be a carrier, your partner should be tested as well.
Carrier screening is different from the NIPT, which screens for chromosomal conditions. They test for different things and are complementary.
| Test | When | What It Checks |
|---|---|---|
| Glucose screening | Weeks 24–28 | 1-hour glucose challenge test for gestational diabetes. If failed, a 3-hour diagnostic test follows. |
| CBC repeat | Weeks 26–28 | Checks for anemia, which is common in the third trimester due to increased blood volume demands. |
| Rh antibody screen | Week 28 | Repeat antibody screen for Rh-negative people. RhoGAM injection given if no antibodies detected. |
| Third-trimester infection screening | Weeks 35–37 | Repeat syphilis, HIV, and/or hepatitis B screening may be done based on risk factors and state requirements. |
| Group B strep (GBS) | Weeks 36–37 | Vaginal/rectal swab (not a blood test) to screen for GBS colonization. Positive results mean IV antibiotics during labor. |
The glucose screening test at 24-28 weeks checks for gestational diabetes. You drink a sugary solution and have your blood drawn one hour later. About 15 to 25 percent of people fail this initial screening and need the three-hour diagnostic test. Most of those who fail the one-hour test do not have gestational diabetes.
Drink plenty of water in the hours before your appointment. Well-hydrated veins are easier to draw from, which means fewer attempts and less discomfort. This is especially helpful for the first-visit panel, which requires multiple vials.
Pregnancy blood work follows a clear timeline: comprehensive screening at the first visit, optional genetic screening in the first trimester, glucose and anemia checks in the second trimester, and final screening in the third trimester. The Group B strep test at 36-37 weeks is a swab rather than a blood test but is part of the same testing sequence.
For the complete schedule of every prenatal appointment and what happens at each one, see our prenatal visit schedule. And make sure your prenatal vitamins are covering the nutritional basics, especially iron if your CBC shows borderline levels.
This guide is for informational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider with any questions about your pregnancy.
