Blood Tests During Third Trimester: Why They Are Important

Blood tests during the third trimester help doctors monitor :

your health, identify potential complications, and ensure both you and your baby are ready for a safe delivery.

As your pregnancy progresses into the third trimester, you may notice that your healthcare provider orders additional blood tests.

For many expectant mothers, this can raise questions and concerns.

Common questions include:

• Why are more blood tests needed late in pregnancy?
• What conditions are doctors looking for?
• Will these tests affect my baby?
• Are these blood tests routine?
• What happens if a result is abnormal?

The final weeks of pregnancy are an important time for monitoring both maternal and fetal health.

Late pregnancy blood tests help healthcare providers identify potential complications, guide treatment decisions, and ensure the safest possible outcome for both mother and baby.

As a women’s health physiotherapist, I often reassure expectant mothers that these tests are not performed because something is necessarily wrong.

Instead, they are designed to detect problems early, often before symptoms develop.

Understanding the purpose of late pregnancy blood tests can help you feel informed, prepared, and more confident as your due date approaches.

Why Are Blood Tests Important in Late Pregnancy?

Pregnancy places significant demands on the body.

During the third trimester:

• Blood volume reaches its peak.
• Nutritional requirements increase.
• The placenta continues to support fetal growth.
• Pregnancy-related complications may emerge.

Blood tests help healthcare providers:

• Detect maternal anemia.
• Screen for infections.
• Monitor chronic medical conditions.
• Identify pregnancy complications.
• Assess maternal organ function.
• Plan labour and delivery safely.

Many pregnancy complications initially develop without obvious symptoms.

Routine blood testing allows healthcare teams to intervene early and improve outcomes.

Complete Blood Count (CBC)

One of the most common late pregnancy blood tests is the Complete Blood Count (CBC).

A CBC evaluates:

• Hemoglobin.
• Hematocrit.
• Red blood cell count.
• White blood cell count.
• Platelet count.

Why Is a CBC Important?

A CBC helps detect:

• Anemia.
• Infection.
• Blood disorders.
• Low platelet count.

Hemoglobin and Anemia

Iron requirements increase substantially during pregnancy.

Low hemoglobin levels may indicate anemia.

Symptoms of anemia may include:

• Fatigue.
• Weakness.
• Dizziness.
• Shortness of breath.
• Palpitations.

Untreated maternal anemia may increase the risk of:

• Preterm birth.
• Low birth weight.
• Maternal complications during delivery.

The World Health Organization estimates that anemia affects a substantial proportion of pregnant women worldwide.

Platelet Count

Platelets help blood clot normally.

Low platelet levels may occur due to:

• Gestational thrombocytopenia.
• Preeclampsia.
• HELLP syndrome.
• Immune conditions.

Monitoring platelet count is especially important if epidural anesthesia is being considered.

Blood Group and Antibody Screening

Blood grouping and antibody screening are usually performed early in pregnancy, but repeat testing may be recommended later in selected situations.

The test determines:

• ABO blood group.
• Rhesus (Rh) status.
• Presence of red blood cell antibodies.

Why Is Rh Status Important?

Women who are Rh-negative may require anti-D immunoglobulin to prevent Rh sensitization.

Rh sensitization occurs when maternal antibodies develop against fetal red blood cells.

Without treatment, future pregnancies may be affected.

Routine antenatal anti-D prophylaxis has significantly reduced complications related to Rh incompatibility.

Iron Studies

Some women undergo additional testing to assess iron status during late pregnancy.

Common tests include:

• Serum ferritin.
• Serum iron.
• Transferrin saturation.

Iron deficiency remains the most common cause of anemia during pregnancy.

Research demonstrates that maternal iron deficiency may adversely affect both maternal well-being and fetal development. (Noran et al. 2015)

Blood Sugar Testing

Women who were not previously diagnosed with gestational diabetes may occasionally require repeat blood sugar testing during late pregnancy.

Additional testing may be recommended if:

• Excessive fetal growth is noted.
• Excess amniotic fluid develops.
• Sugar is detected in the urine.
• New symptoms emerge.

Tests may include:

Oral Glucose Tolerance Test (OGTT)

This evaluates how efficiently the body processes glucose.

Random Blood Glucose Testing

Random glucose measurements may sometimes be used in specific clinical situations.

Untreated gestational diabetes may increase the risk of:

• Large-for-gestational-age babies.
• Birth complications.
• Neonatal hypoglycemia.

According to the John, timely identification and management of gestational diabetes improve maternal and neonatal outcomes. (John et al. 2025)

Liver Function Tests (LFTs)

Liver function tests assess:

• ALT.
• AST.
• Bilirubin.
• Alkaline phosphatase.

These tests may be performed if a woman experiences:

• Severe itching.
• High blood pressure.
• Upper abdominal pain.
• Suspected preeclampsia.

LFTs help identify conditions such as:

• Intrahepatic cholestasis of pregnancy.
• HELLP syndrome.
• Preeclampsia.
• Liver disease.

Kidney Function Tests

Pregnancy complications can affect kidney function.

Common kidney tests include:

• Serum creatinine.
• Blood urea nitrogen.
• Electrolytes.

Kidney function testing is often recommended when:

• Blood pressure is elevated.
• Protein is detected in the urine.
• Preeclampsia is suspected.
• Chronic kidney disease exists.

Abnormal kidney function requires close monitoring throughout pregnancy.

Infection Screening in Late Pregnancy

Additional infection screening may be recommended depending on individual circumstances and local guidelines.

Testing may include:

Group B Streptococcus (GBS) Screening

Usually performed between 35 and 37 weeks of pregnancy.

Repeat HIV, Hepatitis B, and Syphilis Testing

Repeat testing may be recommended for women at increased risk of infection.

Early identification allows timely treatment and reduces the risk of transmission to the baby.

Coagulation Tests

Coagulation studies assess the body’s ability to form blood clots.

These tests may include:

• Prothrombin time (PT).
• Activated partial thromboplastin time (aPTT).
• Fibrinogen levels.

Coagulation testing may be indicated in women with:

• Severe preeclampsia.
• HELLP syndrome.
• Liver disease.
• Bleeding disorders.

A Physiotherapist’s Perspective: Blood Tests Are Preventive Care

As a women’s health physiotherapist, I often meet mothers who become anxious when additional blood tests are ordered late in pregnancy.

Remember that these investigations are primarily preventive.

Most blood tests are performed to identify potential concerns before symptoms develop, allowing timely treatment and safer pregnancy outcomes.

Attending all antenatal appointments and completing recommended investigations remain important parts of prenatal care.

Blood Tests for Preeclampsia

Preeclampsia is a serious pregnancy complication characterised by high blood pressure and signs of organ dysfunction.

If preeclampsia is suspected, healthcare providers may order additional blood tests to evaluate maternal health.

These tests commonly include:

Complete Blood Count (CBC)

A CBC helps assess:

• Platelet count.
• Hemoglobin levels.
• Evidence of hemolysis.

Low platelet levels may indicate severe disease or HELLP syndrome.

Liver Function Tests

Elevated liver enzymes may suggest:

• Preeclampsia.
• HELLP syndrome.
• Liver involvement.

Kidney Function Tests

Abnormal kidney function can occur in preeclampsia.

Healthcare providers often assess:

• Serum creatinine.
• Blood urea nitrogen.
• Electrolytes.

According to Whom, laboratory testing is essential for assessing disease severity and guiding management decisions in women with hypertensive disorders of pregnancy. (Laura et al. 2014)

Blood Tests for Intrahepatic Cholestasis of Pregnancy (ICP)

Some women develop severe itching during late pregnancy.

Healthcare providers may investigate for Intrahepatic Cholestasis of Pregnancy (ICP).

Blood tests may include:

• Liver function tests.
• Serum bile acid levels.

Elevated bile acids may increase fetal risks, including preterm birth and stillbirth.

Prompt diagnosis allows healthcare providers to initiate appropriate treatment and determine optimal timing of delivery.

Research has demonstrated that elevated bile acid concentrations are associated with adverse perinatal outcomes. (Ovadia et al. 2019)

How Often Are Blood Tests Repeated?

The frequency of blood testing depends on:

• Maternal health.
• Gestational age.
• Presence of pregnancy complications.
• Existing medical conditions.
• Previous abnormal results.

Some women require only routine investigations.

Others may require:

• Weekly testing.
• Twice-weekly monitoring.
• Daily blood investigations during hospital admission.

Women with conditions such as:

• Preeclampsia.
• Gestational diabetes.
• Cholestasis.
• Autoimmune disorders.

often require more frequent surveillance.

Blood Tests Before Labour or Cesarean Birth

Additional blood tests may be performed shortly before labour or a planned cesarean birth.

These tests help healthcare providers prepare for delivery safely.

Common pre-delivery investigations include:

Complete Blood Count

To evaluate:

• Hemoglobin levels.
• Platelet count.

Blood Group and Crossmatch

Crossmatching ensures compatible blood is available if transfusion becomes necessary.

Coagulation Studies

These tests may be required if:

• Bleeding risk is increased.
• Epidural anesthesia is planned.
• Severe preeclampsia is present.

Emergency Blood Testing During Pregnancy

Urgent blood tests may be required if complications develop.

Emergency assessment may be necessary when women experience:

• Severe hypertension.
• Heavy vaginal bleeding.
• Reduced fetal movements.
• Severe abdominal pain.
• Severe headache.
• Seizures.

Emergency investigations allow healthcare providers to rapidly assess maternal and fetal status and determine appropriate treatment.

What Happens If Results Are Abnormal?

Abnormal blood test results do not always indicate a serious problem.

Instead, abnormal findings often guide further evaluation.

Possible next steps may include:

• Repeat blood testing.
• Additional urine tests.
• Ultrasound examinations.
• Fetal monitoring.
• Medication.
• Referral to specialists.
• Hospital admission.

Management depends on:

• The specific abnormality.
• Gestational age.
• Maternal symptoms.
• Overall pregnancy health.

Can Blood Tests Harm the Baby?

No.

Routine maternal blood tests do not directly affect the baby.

Blood samples are obtained from the mother’s bloodstream and pose minimal risk.

Some women may experience:

• Mild discomfort.
• Bruising at the needle site.
• Temporary dizziness.

Serious complications are extremely uncommon.

Limitations of Blood Tests

Although blood tests provide valuable information, no single investigation can predict every pregnancy complication.

Blood tests cannot:

• Guarantee a complication-free pregnancy.
• Predict labour onset.
• Identify all fetal problems.
• Replace clinical assessment.

Healthcare providers interpret blood results alongside:

• Blood pressure measurements.
• Urine testing.
• Ultrasound findings.
• Maternal symptoms.
• Fetal surveillance.

Clinical decisions are rarely based on one isolated result.

A Physiotherapist’s Perspective: Understanding the Purpose of Testing

Many expectant mothers become concerned when additional blood tests are ordered late in pregnancy.

As a women’s health physiotherapist, I encourage women to view these investigations as an important safety tool rather than a cause for alarm.

Routine and targeted blood testing allow healthcare providers to detect problems early, monitor maternal health, and support safer pregnancy outcomes.

Remaining engaged in your prenatal care and discussing any concerns with your healthcare team can help reduce anxiety and improve confidence during the final weeks of pregnancy.

Questions You May Want to Ask Your Doctor

Consider asking:

• Why has this blood test been recommended?
• What conditions are being investigated?
• Do I need to prepare for the test?
• What happens if the result is abnormal?
• Will my baby require additional monitoring?
• How often will blood tests need to be repeated?

Preparing questions before appointments can improve understanding and support informed decision-making.

Conclusion

Late pregnancy blood tests play a vital role in modern prenatal care.

By identifying complications early, monitoring maternal health, and guiding treatment decisions, these investigations help support safer outcomes for both mother and baby.

Although additional testing may sometimes feel overwhelming, it is important to remember that most blood tests are performed to provide reassurance and ensure the healthiest possible pregnancy journey.

Frequently Asked Questions (FAQs)

1. What blood tests are commonly performed during late pregnancy?

Common late pregnancy blood tests include Complete Blood Count (CBC), blood sugar testing, liver and kidney function tests, blood group and antibody screening, and infection screening.

2. Why are blood tests repeated during the third trimester?

Blood tests may be repeated to monitor maternal health, detect pregnancy complications, assess treatment effectiveness, or prepare for labour and delivery.

3. Can late pregnancy blood tests detect preeclampsia?

Yes. Blood tests can help identify organ involvement associated with preeclampsia by assessing liver function, kidney function, platelet count, and other markers.

4. Are blood tests during pregnancy safe for my baby?

Yes. Routine maternal blood tests are generally very safe and do not directly affect the baby.

5. What happens if a blood test result is abnormal?

Abnormal results may lead to repeat testing, additional investigations, closer monitoring, medication, or referral to a specialist, depending on the findings.

6. Do all pregnant women need late pregnancy blood tests?

Most women undergo routine blood tests during pregnancy, while some may require additional investigations based on their medical history or pregnancy complications.

Stay tuned with us for more health related topics.

Follow us on LinkedIn and Instagram for more.

Medical Disclaimer!

This article has been reviewed and written under the guidance of our Head Physiotherapist, Dr. Kruti Raj (PT, MUHS,CPT,CMPT). The information shared is intended for educational purposes only and should not be considered a substitute for personalized medical advice, diagnosis, or treatment.

Please consult us or any other qualified healthcare professional before beginning any exercise program, especially if you are experiencing pain, recovering from injury, or managing a medical condition.