August 12, 2023 Updated on July 01, 2026

Prenatal blood tests by trimester: A complete guide to lab work before and during pregnancy

by Lisa Dreher, MS, RDN, LDN
updated by Raegen Barger, RDN, LD, IFNCP

Preconception

Pregnancy

Supplements & Science

If you have ever sat in a waiting room wondering what all those vials of blood are actually checking for, you are not alone. You roll up your sleeve, someone draws a few tubes, and a week or two later you hear that everything looks "normal," often without much explanation of what was measured or why it matters.

Understanding your prenatal blood tests can help you feel more informed and more involved in your own care. Pregnancy places real demands on the body, and lab work is one of the main tools your provider uses to make sure both you and your baby are well supported across each trimester. Some tests are part of standard prenatal care everywhere. Others are worth a conversation, especially if you have specific symptoms, a relevant health history, or a desire to look more closely at your nutrient status.

This guide walks through prenatal blood tests by trimester in plain language. We will cover the standard panels you can expect, the nutrient markers that often come up in preconception and prenatal nutrition conversations, and how to talk with your provider about what makes sense for you. None of this replaces individualized medical advice, but it can help you walk into your appointments with better questions and more confidence.

Prenatal blood tests change across pregnancy. Early on, standard labs typically include a complete blood count, blood type and antibody screen, and screening for certain infections, along with optional genetic screening. Additional nutrient markers like iron studies, vitamin D, and thyroid function may be checked based on your symptoms, history, and provider judgment. Around 24 to 28 weeks, most people are screened for gestational diabetes and rechecked for anemia.

Key Takeaways

Prenatal lab work is organized loosely by trimester, with the heaviest panel of standard tests typically drawn at your first prenatal visit.
Some tests, such as a complete blood count, blood typing, and infection screening, are part of routine prenatal care for nearly everyone.
Other tests, including certain nutrient and thyroid markers, are ordered based on individual risk factors, symptoms, and provider judgment rather than given to everyone automatically.
Gestational diabetes screening usually happens around 24 to 28 weeks, with earlier screening considered for some people who have specific risk factors.
Preconception is a valuable window to check key nutrient markers and address any gaps before pregnancy increases the demand on your body.

Why prenatal blood tests matter

Prenatal blood tests give your provider a window into how your body is adapting to pregnancy and whether anything needs closer attention. Pregnancy changes nearly every system in the body. Blood volume expands significantly, the demand for certain nutrients rises, hormone levels shift, and the body works to support a growing placenta and baby.

Lab work helps catch issues that may not cause obvious symptoms yet, such as low iron stores, an underactive thyroid, or rising blood sugar. It also establishes a baseline early in pregnancy that your provider can compare against later results. Many of the conditions screened for during pregnancy are far easier to support when they are identified early.

It helps to know that there are two broad categories of prenatal testing. Standard or routine tests are recommended for nearly all pregnant people because the evidence consistently supports them. Risk-based or individualized tests are ordered when something in your history, symptoms, or earlier results suggests a closer look would be helpful. Understanding which category a test falls into can make conversations with your provider clearer and less overwhelming.

What is the difference between a screening test and a diagnostic test?

A screening test estimates the likelihood that a condition is present. It does not give a yes or no answer. A diagnostic test is designed to confirm or rule out a condition more definitively. Many prenatal blood tests are screening tests, which is why a result outside the typical range often leads to a follow-up conversation or additional testing rather than an immediate diagnosis. Knowing this distinction can ease some of the worry that comes with an unexpected result.

Preconception blood tests: Building a strong foundation before pregnancy

The months before pregnancy are one of the most underused windows for proactive lab work. Checking in on your health before conception gives you time to address nutrient gaps, understand your baseline, and enter pregnancy with stronger reserves rather than trying to catch up once demands are already high.

While preconception testing should always be individualized, some markers that often come up in preconception nutrition and fertility conversations include:

Complete blood count (CBC): A broad snapshot of red and white blood cells that can flag anemia and other concerns.
Ferritin and iron studies: Ferritin reflects stored iron, which can be low even before anemia develops. Iron status is closely tied to energy and overall reproductive health.
Vitamin D (25-hydroxyvitamin D): A widely deficient nutrient that plays a role in immune function, bone health, and pregnancy outcomes.
Thyroid function: Often discussed for people with symptoms or a personal or family history of thyroid conditions, since thyroid health is connected to fertility and early pregnancy.
Hemoglobin A1c and fasting glucose: Markers of average and fasting blood sugar that can offer insight into metabolic health before pregnancy.
Vitamin B12 and folate status: Nutrients central to cell division and early fetal development.

These markers are not a universal checklist, and not everyone needs every test. They are simply common starting points for a conversation with a provider who can tailor recommendations to your history, your diet, and your goals.

First trimester blood tests: The standard prenatal panel

The first prenatal visit usually includes the most comprehensive round of lab work in the entire pregnancy. Major obstetric organizations recommend a standardized panel of tests for every new pregnancy, ideally early in the first trimester. According to clinical guidance, this initial panel typically includes a complete blood count, blood type and Rh status, an antibody screen, and screening for several infections such as rubella immunity, syphilis, hepatitis B, and HIV.

Here is a closer look at what these standard first trimester tests are checking and why.

Complete blood count (CBC)

A complete blood count measures your red blood cells, white blood cells, hemoglobin, and platelets. In pregnancy, it is especially useful for identifying anemia, which is common as blood volume expands. Catching low hemoglobin early gives you and your provider time to address it through diet, supplementation, or further testing.

Blood type, Rh status, and antibody screen

Knowing your blood type and Rh status matters because of a situation called Rh incompatibility, which can occur when a person who is Rh negative carries an Rh positive baby. The antibody screen checks for antibodies that could affect the pregnancy. This information allows your provider to plan appropriate care, including a preventive treatment when indicated.

Infection screening

Standard prenatal care includes screening for certain infections that can affect pregnancy or be passed to the baby. This typically includes checking immunity to rubella and screening for syphilis, hepatitis B, and HIV. Identifying these early allows for treatment or monitoring that can meaningfully protect both parent and baby.

Optional genetic screening

The first trimester is also when genetic screening is often discussed. First trimester combined screening, usually performed between about 10 and 13 weeks, pairs a blood test with an ultrasound measurement to estimate the chance of certain chromosomal conditions. Cell-free DNA screening, sometimes called noninvasive prenatal screening, is another blood-based option. These are screening tests, not diagnostic tests, and they are offered as a choice rather than required. A genetic counselor or your provider can help you decide what feels right for you.

The first trimester panel establishes your baseline and screens for issues that benefit from early identification. Most of these tests are recommended for nearly all pregnancies, while genetic screening is offered as an informed choice.

Nutrient and hormone markers worth discussing with your provider

Beyond the standard panel, several nutrient and hormone markers frequently come up in prenatal nutrition conversations. It is important to be clear that not all of these are recommended as universal tests. Some are ordered based on symptoms, history, or provider judgment. Understanding the nuance can help you have a more productive discussion rather than requesting every test without context.

Iron and ferritin

Iron needs rise substantially during pregnancy as blood volume expands and the body supports the placenta and baby. A complete blood count can reveal anemia, but ferritin offers earlier insight because it reflects stored iron, which can drop before hemoglobin does. Many people feel symptoms like fatigue, shortness of breath, or restless legs when iron stores are low, even before they meet the formal definition of anemia.

If you have a history of low iron, heavy periods before pregnancy, or symptoms that suggest depletion, asking your provider about ferritin and a full iron panel can be worthwhile. A full iron panel may include serum iron, ferritin, transferrin, and total iron-binding capacity.

Vitamin D

Vitamin D plays a role in immune function, bone health, and several aspects of pregnancy. Deficiency is common across many populations, which is one reason it comes up so often in prenatal nutrition discussions. Research on vitamin D and pregnancy continues to evolve. Some systematic reviews and meta-analyses suggest that vitamin D supplementation, particularly when started early in pregnancy, may be associated with a lower risk of certain complications such as preeclampsia and gestational diabetes, while other analyses describe the evidence as still uncertain and call for more research.

It is worth knowing that major obstetric guidance does not currently recommend universal vitamin D screening for all pregnant people. Instead, testing 25-hydroxyvitamin D can be considered for those thought to be at increased risk of deficiency, with results interpreted in the context of the individual situation. If you are curious about your vitamin D status, this is a reasonable topic to raise with your provider.

Thyroid function

Thyroid health is genuinely important in pregnancy. Overt thyroid disease, both underactive and overactive, is associated with adverse outcomes and clearly benefits from treatment. At the same time, the question of who should be tested is more nuanced than it may appear.

Major organizations, including the American College of Obstetricians and Gynecologists and the American Thyroid Association, do not currently recommend universal thyroid screening for all pregnant people. Instead, they generally support a targeted approach that tests people with symptoms or risk factors, such as a personal or family history of thyroid disease, known thyroid antibodies, type 1 diabetes, or other relevant factors. There is also ongoing professional debate about how to handle milder, subclinical thyroid findings, since the benefit of treating them is less clear.

This is a meaningful update from older guidance that sometimes suggested a full thyroid panel for everyone each trimester. If you have a history of thyroid issues, are taking thyroid medication, or have symptoms that concern you, a thyroid evaluation is very reasonable to discuss. Your provider can help determine whether testing and which specific markers make sense for your situation.

Blood sugar and insulin

Blood sugar regulation is closely tied to both maternal and fetal health. Standard care includes gestational diabetes screening later in pregnancy, which we cover below. For people with certain risk factors, earlier blood sugar testing is sometimes considered. Markers like hemoglobin A1c and fasting glucose can offer insight into glucose patterns, and some guidance supports early testing in people who are overweight or obese with additional risk factors. As with other tests, the right approach depends on your individual history.

A note on optimal versus normal lab ranges

You may hear the terms "normal" and "optimal" used differently depending on who is interpreting your labs. Standard reference ranges are designed to flag clinically significant problems. Some practitioners, particularly those with functional or integrative training, may also consider narrower ranges they describe as optimal, especially for nutrient markers like ferritin and vitamin D.

Second trimester blood tests: Screening as pregnancy progresses

The second trimester brings its own set of tests, with a major focus on screening for gestational diabetes and, in some cases, additional genetic screening.

Gestational diabetes screening

Gestational diabetes screening is a standard part of prenatal care, typically performed between 24 and 28 weeks. The most common approach in the United States is a two-step method. The first step is a glucose challenge test, where you drink a sweet solution and have your blood sugar measured one hour later. If that result is above a certain threshold, a longer diagnostic glucose tolerance test follows to confirm or rule out gestational diabetes.

For people with specific risk factors, such as a higher body mass index combined with other factors, providers may consider screening earlier in pregnancy. It is important to know that even if early screening is normal, repeat screening between 24 and 28 weeks is still recommended, because gestational diabetes often develops later in pregnancy as insulin resistance naturally increases. Newer research continues to refine exactly who benefits most from early screening, but the standard 24 to 28 week screening remains a cornerstone of prenatal care.

Repeat anemia screening

Because iron demands climb as pregnancy progresses, your provider will often recheck your complete blood count around the same time as gestational diabetes screening. This helps catch anemia that may have developed since your first trimester labs.

Second trimester genetic screening

For those who did not complete first trimester genetic screening, or who want additional information, a second trimester blood test sometimes called the quad screen can be offered. It screens for certain chromosomal conditions and, importantly, for open neural tube defects such as spina bifida. As with first trimester screening, these are optional screening tests rather than diagnostic tests.

The second trimester centers on gestational diabetes screening around 24 to 28 weeks, a repeat check for anemia, and optional genetic screening for those who want it.

Third trimester blood tests: Preparing for delivery

In the third trimester, lab work shifts toward preparing for a safe delivery and the postpartum period.

Common third trimester tests may include:

Repeat complete blood count: To check hemoglobin and platelet levels as you approach delivery, since anemia can affect recovery and platelets matter for delivery planning.
Group B Streptococcus (GBS) screening: Usually performed around 36 to 37 weeks. While this is typically done with a swab rather than a blood test, it is an important part of late pregnancy screening.
Repeat infection screening when indicated: Some infection tests may be repeated based on individual risk factors and local guidance.

Your provider may order additional tests based on how your pregnancy is progressing, any symptoms you are experiencing, or specific conditions being monitored. This is also a good time to think ahead to postpartum recovery, when checking iron status again can be especially helpful for people who experienced anemia during pregnancy or significant blood loss at delivery.

How to talk with your provider about prenatal lab work

You do not need a medical degree to be an active participant in your prenatal care. A few thoughtful questions can go a long way toward helping you feel informed and supported.

Consider asking your provider:

Which tests are standard for everyone, and which are you recommending specifically for me and why?
Can we check my ferritin in addition to a complete blood count, especially given my history?
Am I a candidate for thyroid testing based on my symptoms or family history?
Should we discuss vitamin D testing given my individual risk factors?
When will my gestational diabetes screening happen, and is earlier screening appropriate for me?
How will we follow up on any results that fall outside the typical range?

If you want a more individualized, nutrition-focused approach, you may also choose to work alongside a registered dietitian or a functional or integrative medicine practitioner in addition to your primary obstetric provider. Collaborative care that keeps your whole team informed tends to serve you best.

What should both partners know?

While prenatal lab work focuses on the pregnant person, preconception health is a shared journey. Partners can support the process in meaningful ways, from attending appointments to taking ownership of their own health before conception.

For male partners specifically, preconception is a worthwhile time to check in on overall health markers and focus on nutrition, sleep, stress, and lifestyle, all of which can influence sperm health. Sperm are continuously produced and tend to respond to lifestyle changes over a window of roughly two to three months, which makes the preconception period an empowering time to participate rather than wait on the sidelines.

When both partners approach preconception as a team, the entire experience tends to feel more shared and less isolating. Lab work and health optimization stop being something one person carries alone and become part of a joint effort.

When to talk to your provider

Lab work is most valuable when it is interpreted in the context of your full health picture by a qualified provider. Reach out to your healthcare provider if you:

Are planning to conceive and want to establish a preconception baseline.
Have symptoms such as persistent fatigue, shortness of breath, dizziness, hair shedding, or feeling unusually depleted.
Have a personal or family history of thyroid disease, diabetes, anemia, or other relevant conditions.
Receive a lab result outside the typical range and want to understand what it means
.
Are unsure which tests are appropriate for your individual situation.

Always talk with your healthcare provider before adding or changing any supplement, and before requesting or skipping any test. Personalized guidance matters, because the right plan depends on your unique history, diet, and pregnancy.

Frequently asked questions about prenatal blood tests

What blood tests are done in the first trimester of pregnancy?

The first trimester typically includes the most comprehensive panel of the pregnancy. Standard tests usually include a complete blood count, blood type and Rh status, an antibody screen, and screening for certain infections such as rubella immunity, syphilis, hepatitis B, and HIV. Optional genetic screening, including first trimester combined screening or cell-free DNA testing, is also offered during this time.

How often are blood tests done during pregnancy?

Blood tests are generally clustered at key points rather than at every visit. The largest panel is drawn at the first prenatal visit. Gestational diabetes screening and a repeat anemia check usually happen around 24 to 28 weeks, and additional tests, including a repeat complete blood count, may be done in the third trimester as you approach delivery. Your provider may order more frequent testing based on your individual situation.

Do I need my thyroid checked during pregnancy?

Not everyone needs thyroid testing. Major guidelines do not currently recommend universal thyroid screening for all pregnant people and instead support testing those with symptoms or risk factors, such as a personal or family history of thyroid disease or known thyroid antibodies. If you have a relevant history, are on thyroid medication, or have symptoms, discussing thyroid testing with your provider is reasonable.

Should I ask for a ferritin test in addition to a CBC?

It can be worth discussing. A complete blood count can identify anemia, but ferritin reflects stored iron, which may be low before anemia develops. If you have a history of low iron, heavy periods before pregnancy, or symptoms of depletion, asking your provider about ferritin and a full iron panel may provide a more complete picture.

When is gestational diabetes screening done?

Gestational diabetes screening is typically performed between 24 and 28 weeks of pregnancy. People with certain risk factors may be screened earlier, but even with a normal early result, repeat screening at 24 to 28 weeks is still recommended because gestational diabetes often develops later in pregnancy.

What is the difference between iron deficiency and iron deficiency anemia?

Iron deficiency means your iron stores are low, which can happen before your red blood cell levels become abnormal. Iron deficiency anemia means stores are low enough that your body is no longer making enough healthy red blood cells or hemoglobin. Many people feel symptomatic with low ferritin before they meet the formal criteria for anemia, which is one reason ferritin testing can be helpful.

A note from WeNatal on prenatal blood tests by trimester

At WeNatal, we believe that feeling informed is part of feeling supported. Prenatal lab work is one of the most valuable tools you have for understanding your body during pregnancy, and you deserve to know what is being checked and why. The goal is never to add pressure or turn pregnancy into a series of numbers to perfect. It is to help you walk into each appointment with confidence and good questions.

Lab work and nutrition go hand in hand. Many of the markers discussed here, from iron to vitamin D, reflect nutrient status that thoughtful supplementation and a nourishing diet can help support over time. That is exactly why we formulated our prenatal nutrition with absorption and tolerance in mind, including a gentle, well-absorbed form of iron paired with vitamin C in WeNatal Iron+, and a comprehensive foundation of methylated B vitamins, choline, iodine, and more in WeNatal for Her. Supplements are one part of a larger picture that works best alongside whole foods, healthy habits, and care from your provider.

Wherever you are in your journey, from preconception to postpartum, your body deserves support that honors the whole experience. Because the goal is never just to get through pregnancy. It is to feel nourished, informed, and cared for as you move from me to we.

Curious where to start? Explore WeNatal for Her and WeNatal Iron+ to support your nutrient foundation, and take our quiz to find the right fit for you and your partner.

References

ACOG Clinical Practice Update: Screening for Gestational and Pregestational Diabetes in Pregnancy and Postpartum. Obstet Gynecol. Published online May 21, 2024. doi:10.1097/AOG.0000000000005612

American College of Obstetricians and Gynecologists. Thyroid Disease in Pregnancy. ACOG Practice Bulletin. Obstet Gynecol. 2020;135(6):e261-e274. doi:10.1097/AOG.0000000000003893

Lee SY, Pearce EN. Assessment and treatment of thyroid disorders in pregnancy and the postpartum period. Nat Rev Endocrinol. 2022;18(3):158-171. doi:10.1038/s41574-021-00604-z

Moghib K, Ghonim HA, Ghonim MA, et al. Efficacy of vitamin D supplementation on the incidence of preeclampsia: a systematic review and meta-analysis. BMC Pregnancy Childbirth. 2024;24(1):852. doi:10.1186/s12884-024-07081-y

Quintanilla Rodriguez BS, Mahdy H. Initial Antepartum Care. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2024. Available from: https://www.ncbi.nlm.nih.gov/books/NBK570635/

Tantengco OAG, Vink J, et al. Screening for Maternal Thyroid Dysfunction in Pregnancy: A Review of the Clinical Evidence and Current Guidelines. J Thyroid Res. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3671674/

US Preventive Services Task Force; Gestational Diabetes Mellitus: Update on Screening, Diagnosis, and Management. Am Fam Physician. 2023;108(3):249-258. Available from: https://www.aafp.org/pubs/afp/issues/2023/0900/gestational-diabetes.html

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent disease. This article is educational and is not a substitute for personalized medical advice.

Lisa Dreher, MS, RDN, LDN

Lisa is the Nutrition Director at WeNatal and Senior Dietitian at Dr. Mark Hyman's UltraWellness Center. She completed her dietetic internship at Cornell University in 2010 and holds a master’s degree in Nutrition and Integrative Health. Lisa has been featured on NPR, the Broken Brain Docuseries, The Doctor's Farmacy and Energized with Dr. Mariza podcasts, and several publications. She led the formulation development of WeNatal for Her, WeNatal for Him, Omega DHA+, and Egg Quality+. With a passion for personalized nutrition, she empowers clients to optimize their health through evidence-based dietary strategies. Lisa has a passion for using food as medicine and has been able to draw from her personal health challenges to foster healing in others.