The booking appointment ends with a row of vials and no explanation of what is in them. They are not one test — they are five or six unrelated ones drawn at the same time, looking for completely different things, and only a couple of them will ever produce a result anyone discusses with you.
This guide goes through them one at a time: what each test is looking for, what the numbers mean, which ones get repeated and why, and which results actually change what happens next.
The short answer: booking bloods cover blood group and rhesus status, an antibody screen, a full blood count for anaemia, and screening for hepatitis B, HIV and syphilis, with sickle cell and thalassaemia screening ideally before 10 weeks. The full blood count and antibody screen are repeated at around 28 weeks. Anaemia in pregnancy means a haemoglobin below 110 g/L in the first trimester and below 105 g/L after it.
What is drawn, and when
| Week | Test | What it is looking for |
|---|---|---|
| Before 10 | Sickle cell and thalassaemia | Inherited haemoglobin disorders. Early, so the baby's father can be tested if needed |
| 8–12 | Blood group and RhD | Whether anti-D prophylaxis will be needed |
| 8–12 | Antibody screen | Red cell antibodies that could affect the baby |
| 8–12 | Full blood count | Anaemia, and platelet count as a baseline |
| 8–12 | Hepatitis B, HIV, syphilis | Infections that are treatable and that affect the baby if untreated |
| 11–14 | PAPP-A and free β-hCG | Part of first trimester screening — a chance figure, not a value |
| From 10 | Cell-free DNA (NIPT) | Chromosomal screening, if offered or requested |
| 24–28 | Glucose tolerance test | Gestational diabetes, if you have a risk factor |
| 28 | Full blood count, repeated | Anaemia developing in the second half of pregnancy |
| 28 | Antibody screen, repeated | New antibodies; decides anti-D if RhD negative |
Two rows on that table are a different kind of test: the first trimester screening bloods and NIPT produce a probability rather than a measurement, and are covered on their own pages. The glucose tolerance test likewise has its own.
Blood group, rhesus status and the antibody screen
Your blood group matters in pregnancy for one reason above all others: the RhD antigen. About 15% of people of European ancestry lack it and are RhD negative.
If you are RhD negative and your baby is RhD positive, any mixing of blood — at birth, after bleeding, a fall, or a procedure like amniocentesis — can prompt your immune system to make antibodies against RhD. Those antibodies do nothing to this baby but would cross the placenta in a future pregnancy and attack a future RhD-positive baby's red cells.
Anti-D immunoglobulin prevents that sensitisation from happening. NICE describes several licensed regimens: two doses of 500 IU at 28 and 34 weeks, two doses of 1,000–1,650 IU at the same points, or a single 1,500 IU dose at 28 weeks or between 28 and 30 weeks. Which one your unit uses determines whether you get a second appointment for it, so it is worth asking rather than assuming.
Anti-D is time-critical after any bleeding. If you are RhD negative and you have vaginal bleeding, abdominal trauma or a fall at any point after 12 weeks, ring your maternity unit the same day — anti-D works best given within 72 hours, and this is one of the few situations in pregnancy where the clock genuinely matters.
The full blood count: haemoglobin and ferritin
Anaemia is the most common abnormal result in pregnancy and the one most often summarised as "your bloods were fine" when it was not quite.
The thresholds are lower than outside pregnancy, deliberately. Plasma volume expands faster than red cell mass, so the concentration falls even when nothing is wrong. UK guidance defines anaemia as a haemoglobin below:
🩸 Anaemia thresholds
- 110 g/L in the first trimester
- 105 g/L in the second and third trimesters
- 100 g/L after birth
Ferritin is the more useful number and is not always measured. Haemoglobin tells you whether you have run out of iron; ferritin tells you whether you are about to. Stores fall before the concentration does, which means a normal haemoglobin with a low ferritin is a chance to fix something before it becomes a problem. UK practice commonly treats a ferritin below 30 µg/L, with 65 mg of elemental iron daily as a standard starting dose.
If you are started on iron, a repeat full blood count after two to three weeks shows whether it is working. Our guide to prenatal supplements covers what to take iron with and what blocks its absorption — tea and coffee at the same time being the most common avoidable mistake.
The three infection screens
Hepatitis B, HIV and syphilis are offered to everyone rather than by risk, and the reason is the same for all three: each can pass to the baby, each is treatable in pregnancy, and treatment dramatically reduces transmission. Risk-based questioning reliably misses people; universal testing does not.
- HIV — with treatment during pregnancy and appropriate care at birth, transmission to the baby is reduced to a very low level.
- Hepatitis B — vaccination and immunoglobulin for the baby at birth prevent most transmission.
- Syphilis — treatable with antibiotics in pregnancy, and serious for the baby if it is not treated.
These are the tests where a positive result changes the most, which is worth weighing separately from the screening tests that only shift a probability.
Rubella: the test that quietly disappeared
Rubella immunity used to be checked at booking everywhere and is still checked in most countries. England stopped routine antenatal rubella screening on 1 April 2016, after the UK National Screening Committee concluded twice that it did not meet the criteria for a screening programme — high MMR coverage had made exposure during pregnancy very unlikely.
The deeper reason is that the result could never help the current pregnancy: rubella immunity cannot be given during pregnancy, so a susceptible result only ever meant "be vaccinated afterwards". Where the test is still done, that remains its only use.
Sickle cell and thalassaemia
These inherited haemoglobin disorders are screened before 10 weeks for a specific reason: if you are found to be a carrier, the baby's father needs testing too, and if he is also a carrier, you are offered counselling and the option of diagnostic testing. That whole sequence takes weeks, and the window for the diagnostic tests is limited.
Being a carrier is not being ill. Carriers are healthy; the question is only what happens if both parents carry the same trait.
Questions worth asking about results
- "What was my haemoglobin, and my ferritin?" Not "were my bloods fine". The numbers are the baseline for everything later.
- "Am I RhD negative, and which anti-D regimen does this unit use?" It determines whether there is a second appointment.
- "Was ferritin actually measured?" It is not always included, and a normal haemoglobin does not exclude low stores.
- "When is this being rechecked?" Most borderline results in pregnancy are managed by repeating the test.
When to call your midwife
Call the same day if: you are RhD negative and have any vaginal bleeding, abdominal trauma or a fall after 12 weeks — anti-D is most effective within 72 hours. Also call the same day for breathlessness at rest, palpitations or feeling faint, which can indicate significant anaemia; for fever; and for the standard reasons at any stage — bleeding, leaking fluid, severe headache with visual disturbance, sudden swelling, or reduced fetal movements after 24 weeks.
Our guide to the antenatal appointment schedule covers when each of these tests fits into the pregnancy, and the full schedule of tests and scans puts the bloods alongside the scans.
Frequently Asked Questions
What blood tests are done at the booking appointment?
Blood group and rhesus status, an antibody screen, a full blood count, and screening for hepatitis B, HIV and syphilis. Sickle cell and thalassaemia screening is offered ideally before 10 weeks. In many countries rubella immunity is also checked, although England stopped routine antenatal rubella screening on 1 April 2016.
What counts as anaemia in pregnancy?
UK guidance sets the threshold at a haemoglobin below 110 g/L in the first trimester, below 105 g/L in the second and third, and below 100 g/L after birth. The thresholds are lower than outside pregnancy because blood volume expands faster than red cell mass, which dilutes the concentration without meaning anything is wrong.
What is ferritin and why does it matter more than haemoglobin?
Ferritin measures your iron stores, while haemoglobin measures the consequence of running out of them. Stores fall first, so ferritin can be low while haemoglobin is still normal — which is the point at which iron works best. UK practice commonly treats a ferritin below 30 µg/L, and at that level 65 mg of elemental iron once a day is a standard starting dose.
Why are blood tests repeated at 28 weeks?
Because two things change over the second half of pregnancy. Anaemia commonly develops as the baby draws on iron stores, so the full blood count is repeated. And red cell antibodies can appear that were not present at booking, so the antibody screen is repeated too — that result is what the anti-D decision depends on if you are RhD negative.
What does it mean if I am rhesus negative?
It means your red cells lack the RhD antigen. If your baby is RhD positive and your blood mixes with the baby's, your immune system can make antibodies that would attack the red cells of a future RhD-positive baby. Anti-D immunoglobulin prevents that, and is offered from 28 weeks as well as after any event that could cause mixing — bleeding, a fall, an amniocentesis or birth itself.
Why is HIV screening offered to everyone rather than by risk?
Because it works. With diagnosis and treatment in pregnancy, transmission to the baby can be reduced to a very low level, and risk-based testing reliably misses people. The same logic applies to hepatitis B and syphilis: all three are treatable, all three affect the baby if untreated, and all three are found by testing everyone rather than by asking questions.
Is my thyroid checked in pregnancy?
Not routinely in most programmes. Thyroid function is tested when there is a reason — existing thyroid disease, type 1 diabetes, a family history, or symptoms — rather than as universal screening, because the evidence that treating mild subclinical changes improves outcomes has not been strong enough to justify screening everyone.
Can I decline the infection screening?
Yes. It is offered, and declining is recorded and does not affect the rest of your care. It is worth knowing what declining costs: these are the tests where a positive result changes the outcome for the baby most dramatically and most reliably, which is a different calculation from the screening tests that only estimate a probability.
Blood tests in pregnancy — at a glance
Booking bloods cover blood group and rhesus status, an antibody screen, a full blood count and screening for hepatitis B, HIV and syphilis, with sickle cell and thalassaemia screened before 10 weeks so there is time to test the baby's father. The full blood count and antibody screen are repeated at 28 weeks because anaemia commonly develops and new antibodies can appear. Anaemia means a haemoglobin below 110 g/L in the first trimester and below 105 g/L afterwards; ferritin below 30 µg/L is commonly treated, and it falls before haemoglobin does. If you are RhD negative, anti-D immunoglobulin is offered from 28 weeks and after any bleeding or trauma, where it works best within 72 hours. England stopped routine rubella screening in 2016 because the result could never change the current pregnancy.
Inside Baby Novum: the lab results journal keeps each result with its date, gestational week and a photo of the report, so your booking haemoglobin is still there to compare against the 28-week one. The supplement tracker follows iron alongside the rest, with optional reminders — which matters, because iron only works if it is actually taken.
Read next
Sources
- NHS — Screening tests in pregnancy
- Pavord et al., British Journal of Haematology 2020 — UK guidelines on the management of iron deficiency in pregnancy
- UK National Screening Committee, 2016 — Rubella susceptibility screening in pregnancy ends
- NICE TA156 — Routine antenatal anti-D prophylaxis for women who are rhesus D negative
- NHS — Your antenatal appointments