Blood tests are ordered routinely throughout pregnancy — often more than a dozen separate panels across three trimesters. Many expectant mothers receive results without a full explanation of what each test checks or why it matters.
This guide walks through what's typically tested at each stage of pregnancy, what the key results mean, and what to do if something comes back out of range.
First trimester: the booking blood tests (weeks 8–12)
The first appointment with a midwife or obstetrician usually includes a comprehensive panel sometimes called the 'booking bloods'. These establish a baseline and screen for several conditions that matter for the pregnancy.
- Full blood count (FBC) — checks for anaemia and platelet levels
- Blood group and rhesus factor — determines if anti-D injections are needed
- Rubella immunity — confirms whether you're protected against German measles
- Hepatitis B surface antigen — screens for hepatitis B, which can pass to the baby
- HIV test — allows treatment that prevents mother-to-child transmission
- Syphilis (VDRL/TPHA) — treatable if caught early
- Thyroid function (TSH) — uncontrolled thyroid disease increases miscarriage risk
- Down's syndrome screening markers — PAPP-A and HCG, used alongside an ultrasound to calculate risk
First and second trimester: chromosomal screening
Non-invasive prenatal testing (NIPT) is an optional blood test that can be done from around 10 weeks onwards. It analyses fetal DNA circulating in the mother's blood to screen for chromosomal conditions including Down's syndrome (trisomy 21), Edwards' syndrome (trisomy 18) and Patau's syndrome (trisomy 13).
NIPT is a screening test, not a diagnostic test. A high-risk result would typically lead to an offer of diagnostic testing — amniocentesis or chorionic villus sampling — to confirm.
Second trimester: gestational diabetes screening (weeks 24–28)
Gestational diabetes is diabetes that develops during pregnancy. It's screened with a glucose tolerance test (GTT): you fast overnight, drink a glucose solution, and have blood drawn at one and two hours to see how your body handles the sugar.
A diagnosis of gestational diabetes doesn't mean lifelong diabetes — most cases resolve after delivery — but it does require dietary changes, close monitoring and sometimes medication during the remainder of the pregnancy.
Second trimester: repeat full blood count
Anaemia is common in pregnancy, particularly iron-deficiency anaemia, which can cause fatigue, breathlessness and — if severe — complications for the baby. Most guidelines recommend a repeat FBC at around 28 weeks. If haemoglobin is low, iron supplementation (and in some cases IV iron) is started.
Third trimester (weeks 28–36)
- Repeat full blood count — checks haemoglobin heading into labour
- Repeat HIV and syphilis — recommended in many countries as a precaution
- Group B Streptococcus (GBS) swab — not a blood test, but often done around week 35–37 to screen for bacteria that can affect the baby during delivery
- Coagulation screen — if there are concerns about bleeding risk
Keeping your prenatal results together
Prenatal care often involves multiple providers — a GP, an obstetrician, a midwife, a diabetes team. Keeping all your results in one place in Looms means every member of your care team has access to the same complete picture, reducing the risk of something being missed. For a detailed look at the gestational diabetes screen, see our guide to the glucose tolerance test, and for the thyroid panel often ordered in the first trimester, our thyroid blood test guide covers what the numbers mean.