Patient Guide

Pregnancy Blood Tests: Complete Antenatal Testing Guide

Name: Pregnancy Blood Tests | HealthReview
Creator: Suman Konda
Published: 2026-07-05

Pregnancy involves several rounds of blood tests from the first visit to delivery. This guide explains every antenatal blood test, when it's done, and what results mean for you and your baby.

Written by Suman Konda, PharmD, Clinical Pharmacist · Editorial policy · Not medical advice

Last updated: 01 August 2026 · How we check our content

First trimester blood tests (booking visit, 8–12 weeks)

Test	Purpose
Blood group (ABO) and Rh type	Identify Rh-negative mothers who need anti-D injections to prevent haemolytic disease of the newborn
Full Blood Count (FBC)	Detect anaemia early in pregnancy: haemoglobin target ≥11 g/dL in 1st trimester
Ferritin / iron studies	Iron deficiency is the most common pregnancy anaemia: treat before anaemia develops
Rubella antibody (IgG)	Confirm immunity: rubella in pregnancy causes serious birth defects
Syphilis (RPR/VDRL)	Congenital syphilis is preventable: treatment in pregnancy is curative
Hepatitis B (HBsAg)	Babies of HBsAg-positive mothers need vaccination + HBIG at birth
HIV	Treatment in pregnancy reduces mother-to-child transmission to <1%
TSH (Thyroid)	Hypothyroidism in pregnancy risks miscarriage and baby's brain development
Blood pressure + urine protein	Baseline for pre-eclampsia monitoring

Second trimester blood tests (15–20 weeks)

Down syndrome and chromosome screening

The combined first trimester screening (10–14 weeks) uses nuchal translucency ultrasound + PAPP-A + free beta-hCG to assess chromosomal risk. The second trimester quadruple screen (15–20 weeks) uses AFP, hCG, estriol and inhibin-A. Non-invasive prenatal testing (NIPT), a blood test using cell-free fetal DNA, can screen for Down syndrome from 10 weeks with >99% sensitivity. Abnormal results require confirmatory amniocentesis or chorionic villus sampling.

Third trimester blood tests (24–36 weeks)

Test	When	Purpose
Gestational diabetes (OGTT)	24–28 weeks	75g oral glucose tolerance test: GDM affects 5–10% of pregnancies
FBC (repeat)	28 weeks	Iron deficiency anaemia worsens as pregnancy progresses
Antibody screen (repeat)	28 weeks	Check for red cell antibodies in Rh-negative mothers
Group B Streptococcus (GBS)	35–37 weeks	Vaginal swab: GBS in baby can cause serious neonatal infection

Questions to ask your midwife or obstetrician

Am I Rh-negative: do I need anti-D injections?
Is my iron level good: should I take iron supplements?
What are my gestational diabetes screening results?
Has my NIPT or chromosome screening been completed?
What is my thyroid result: do I need treatment?

Why some values shift in pregnancy without anything being wrong

Pregnancy changes physiology enough that several results must be read against pregnancy-specific ranges. Plasma volume expands more than red cell mass, so haemoglobin falls by dilution and a mild anaemia by non-pregnant standards can be normal. Alkaline phosphatase rises because the placenta produces its own. Thyroid binding proteins increase and hCG weakly stimulates the thyroid, so TSH tends to fall in the first trimester. Kidney filtration rises, so creatinine and urea fall, and a creatinine at the upper end of the non-pregnant range may indicate significant impairment. Clotting factors increase, which is why pregnancy is a prothrombotic state.

Screening tests and what a result actually means

Combined and quadruple screening do not diagnose anything. They return a probability, and a screen-positive result means the chance is above a threshold, not that the condition is present; most screen-positive pregnancies are unaffected. Non-invasive prenatal testing analysing cell-free DNA performs considerably better but remains a screening test, with results needing confirmation by amniocentesis or chorionic villus sampling before any irreversible decision. Understanding this distinction before results arrive removes a great deal of avoidable distress.

Tests that lead to action during the pregnancy

Blood group and antibody screen, which determines anti-D prophylaxis in RhD negative women and identifies antibodies that need monitoring.
Haemoglobinopathy screening, where both partners' results together determine the risk to the baby.
Infection screening for HIV, hepatitis B and syphilis, all of which have treatments that markedly reduce transmission to the baby.
Glucose tolerance testing for gestational diabetes, usually between 24 and 28 weeks, earlier with risk factors.
Ferritin and full blood count, since iron deficiency is common and treatable and matters more as delivery approaches.

Symptoms that override any test schedule

Severe headache with visual disturbance, sudden swelling of the face or hands, upper abdominal pain under the ribs, reduced fetal movements, vaginal bleeding, or a leaking of fluid all warrant contacting maternity services immediately rather than waiting for the next appointment. Reduced fetal movement in particular should never be left overnight; the advice to monitor at home has been replaced by advice to be assessed promptly.