How many blood tests are done during pregnancy?

Most pregnant women undergo at least 6 to 8 blood tests across the three trimesters, including CBC, blood type, STI screening, glucose challenge, and optional genetic tests like NIPT.

Is blood taken for all pregnancy tests?

No, some tests like the glucose challenge require drinking a sugary solution before blood draw, and GBS screening involves a swab. However, the majority of routine prenatal screenings are blood-based.

What blood tests are done at 12 weeks pregnant?

At 12 weeks, the first-trimester combined screen (blood for PAPP-A and hCG) is common, along with CBC, blood type, Rh factor, rubella immunity, and STI panel.

Do I need to fast before pregnancy blood tests?

Most prenatal blood tests do not require fasting, except for the glucose tolerance test (OGTT) and sometimes lipid panels. Always follow your provider's instructions.

Can blood tests detect birth defects?

Yes, blood tests like the quad screen and NIPT can estimate the risk of neural tube defects and chromosomal abnormalities such as Down syndrome. They are screening, not diagnostic tests.

What All Blood Tests Are Done During Pregnancy: A Complete Guide

Discover what all blood tests are done during pregnancy today. From first-trimester screening to glucose testing, this guide covers every essential prenatal blood test.

Blood tests during pregnancy are routine medical screenings that monitor the health of both the mother and the developing baby. Today, standard prenatal care in the United States includes a series of blood tests performed at different stages of pregnancy to detect potential complications, confirm blood type, check for infections, and assess genetic risks. These tests help your healthcare provider ensure a safe pregnancy and guide decisions about additional screenings or interventions. Below is a comprehensive, original guide to every common blood test you can expect, organized by trimester.

First-Trimester Blood Tests (Weeks 1–13)

The first trimester is critical for establishing a baseline of maternal health and identifying early risk factors. Your provider will typically order the following blood tests at your initial prenatal visit.

Complete Blood Count (CBC)

A CBC measures red blood cells, white blood cells, hemoglobin, and platelets. It screens for anemia, infections, and clotting disorders. Today, many labs also include a differential count to assess immune function.

Blood Type and Rh Factor

This test determines your ABO blood group (A, B, AB, or O) and Rh factor (positive or negative). If you are Rh-negative, you will need an Rh immunoglobulin shot later in pregnancy to prevent Rh incompatibility with the baby.

Rubella (German Measles) Immunity

A blood test checks for antibodies against rubella. If you are not immune, vaccination is recommended after delivery.

Sexually Transmitted Infection (STI) Screening

Blood tests for syphilis (RPR or VDRL), HIV, hepatitis B, and hepatitis C are standard. Early detection allows treatment to reduce transmission risk to the baby.

First-Trimester Combined Screening (for Down Syndrome and Trisomy 18)

This includes a blood test for pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG), combined with an ultrasound nuchal translucency measurement. Results provide a risk estimate for chromosomal abnormalities.

Second-Trimester Blood Tests (Weeks 14–27)

During the second trimester, additional screenings evaluate fetal development and maternal health.

Quad Screen (Maternal Serum Screening)

This blood test measures four markers: alpha-fetoprotein (AFP), hCG, estriol, and inhibin A. It screens for neural tube defects (like spina bifida), Down syndrome, and trisomy 18. Today, some labs now offer a penta screen adding a fifth marker for improved accuracy.

Glucose Challenge Test (GCT)

Between 24 and 28 weeks, you will drink a sugary solution, and blood is drawn one hour later to screen for gestational diabetes. If the result is elevated, a three-hour oral glucose tolerance test (OGTT) follows for diagnosis.

Anemia Recheck

A repeat CBC may be ordered to ensure hemoglobin levels remain adequate as blood volume expands.

Third-Trimester Blood Tests (Weeks 28–40)

In the final trimester, blood tests focus on preparing for delivery and monitoring late-onset conditions.

Glucose Tolerance Test (if not done earlier)

If you missed the second-trimester screen or have risk factors, the OGTT may be performed now.

Group B Streptococcus (GBS) Screening

While primarily a vaginal/rectal swab, a blood test for GBS antibodies may be used in some practices to assess colonization risk.

Complete Blood Count (CBC) Before Delivery

Another CBC is often ordered near term to check for anemia that could affect blood loss during birth.

HIV and Hepatitis B Repeat

If you are at high risk, a repeat blood test for HIV and hepatitis B may be recommended in the third trimester.

Additional Blood Tests Based on Risk Factors

Depending on your medical history, ethnicity, or symptoms, your provider may order these additional blood tests.

Thyroid function tests (TSH, T4): to detect hypothyroidism or hyperthyroidism, which can affect fetal brain development.
Vitamin D levels: deficiency is common and linked to gestational diabetes and preterm birth.
Iron studies (ferritin, serum iron): for anemia that does not improve with oral supplements.
Genetic carrier screening (e.g., cystic fibrosis, spinal muscular atrophy, sickle cell disease): offered to all pregnant women today per ACOG guidelines.
Cell-free DNA screening (NIPT): a blood test that analyzes fetal DNA for trisomies 21, 18, and 13, and can also determine fetal sex as early as 10 weeks.

Summary Table of Routine Prenatal Blood Tests

Test	Trimester	What It Screens
Complete Blood Count (CBC)	First, Third	Anemia, infection, clotting
Blood Type & Rh Factor	First	Blood group, Rh incompatibility
Rubella Immunity	First	Rubella antibody status
STI Panel (HIV, Hep B, Syphilis)	First (repeat if high risk)	Infections that affect baby
First-Trimester Combined Screen	First	Down syndrome, trisomy 18
Quad Screen	Second	Neural tube defects, trisomies
Glucose Challenge Test	Second	Gestational diabetes
GBS Screening (swab + blood)	Third	Group B Strep colonization

Why These Blood Tests Matter for You and Your Baby

Each blood test provides a snapshot of your health and the pregnancy's progress. Early detection of conditions like anemia, gestational diabetes, or infections allows for timely management, reducing risks of preterm labor, preeclampsia, or birth defects. Today, advances in non-invasive prenatal testing (NIPT) have made genetic screening safer and more accurate, with detection rates above 99% for common trisomies. Your healthcare provider will interpret results in the context of your age, medical history, and ultrasound findings.

Take the Next Step in Your Prenatal Care

Understanding what blood tests are done during pregnancy empowers you to ask informed questions and actively participate in your care. At prenatalscreenings.com, we offer reliable, doctor-reviewed resources and direct access to essential prenatal screening tests. Order your prenatal blood test panel today and gain peace of mind with comprehensive results delivered securely. Your health and your baby's future deserve the best start.