Pregnancy · Blood Type
Blood Type & Inheritance in Pregnancy
ABO + Rh blood type basics, what each parent passes, what Rh-negative means in pregnancy (anti-D pathway from 28 weeks), ABO incompatibility and newborn jaundice. NICE NG201.
Last reviewed 2 June 2026
ABO & Rh inheritance
What blood type will my baby have?
Mother's blood type
ABO group
Rh factor
Father's blood type
ABO group
Rh factor
Pick both parents’ ABO and Rh types to see your baby’s probabilities.
Two blood type systems matter in pregnancy
- ABO (A, B, AB, O): minor incompatibility can cause mild newborn jaundice.
- Rh (positive / negative): if mum Rh-neg and baby Rh-pos, mum can develop antibodies that attack baby’s blood cells in future pregnancies.
Rh-negative pregnancy
- Booking blood test identifies Rh status.
- Antibody screen at booking + 28 weeks.
- Anti-D injection at 28 weeks (and after delivery if baby Rh-pos).
- Some UK trusts: cffDNA at 11-13 wk determines baby’s Rh from mum’s blood.
- Anti-D after any sensitising event (bleeding, trauma, miscarriage, amnio).
See /calculators/anti-d-dosing for full detail.
ABO incompatibility
When mum is O and baby is A or B. Mum’s natural anti-A or anti-B antibodies cross placenta. Usually MILDER than Rh disease.
Presentation: neonatal jaundice in first 24 hours; sometimes anaemia. Treatment: phototherapy usually sufficient; rarely exchange transfusion.
No antenatal prophylaxis for ABO; managed reactively.
Inheritance basics
- O × O → O only.
- A × A → A or O.
- B × B → B or O.
- O × A → O or A.
- AB × anything → many possibilities.
- Both Rh-neg → baby Rh-neg.
- Either Rh-pos → baby could be Rh-pos.
Other antibodies that matter
Besides anti-D: anti-c, anti-Kell, anti-Duffy, anti-Kidd, anti-MNS.
Rare but serious. Antibody screen at booking + 28 wk detects.
Anti-Kell particularly aggressive — severe anaemia at lower titers than anti-D.
Ethnicity
- Caucasian: ~15% Rh-neg.
- Black: ~5-8%.
- East Asian: <1%.
- Basque: ~25% — highest.
- South Asian: ~5%.
Different scenarios
Scenario 1: O-negative mum, O-positive partner
Baby likely Rh-pos. Anti-D pathway. Consider cffDNA at 11-13 wk to confirm.
Scenario 2: O mum, AB baby (after birth)
ABO incompatibility possible. Watch for early jaundice; phototherapy if needed.
Scenario 3: Anti-Kell antibodies found at booking
Specialist fetal medicine. Monitoring MCA Doppler for fetal anaemia. Possible intrauterine transfusion.
Scenario 4: Rh-neg, partner also Rh-neg
Baby Rh-neg. No anti-D needed. Anti-D pathway not relevant.
Scenario 5: cffDNA at 12 weeks shows baby Rh-negative
No anti-D this pregnancy. Saves unnecessary injections.
Care guidance — blood type
- Booking blood tests establish type.
- Rh-neg: anti-D pathway essential.
- cffDNA option at 11-13 wk where available.
- Antibody screen booking + 28 wk.
- Partner’s type helpful but not essential.
- ABO usually self-resolves with phototherapy if needed.
- O-type mums: watch for early newborn jaundice.
- Rare antibodies: specialist fetal medicine care.
Sources
- NICE NG201. Antenatal care.
- RCOG Green-top Guideline 22. Anti-D immunoglobulin.
- NHS Blood and Transplant. nhsbt.nhs.uk.
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Frequently asked questions
What does my blood type mean in pregnancy?
TWO MAIN SYSTEMS matter: (1) ABO (A, B, AB, O) — generally not a pregnancy issue; minor incompatibility can cause mild newborn jaundice. (2) RH (positive / negative) — if mum is Rh-NEGATIVE and baby Rh-POSITIVE, mum can develop antibodies that attack baby's blood cells in future pregnancies. ROUTINELY tested at booking blood test in pregnancy. ~15% of Caucasian women are Rh-negative; lower in Asian / Black populations.
What does Rh-negative mean for my pregnancy?
(1) BOOKING BLOOD TEST identifies; (2) ANTIBODY SCREEN at booking + 28 weeks to check for existing anti-D antibodies; (3) ANTI-D injection at 28 weeks (and after delivery if baby Rh-pos) prevents YOU developing antibodies; (4) SOME UK trusts: cffDNA (free fetal DNA) test from your blood at 11-13 wk determines BABY'S Rh — if Rh-neg, no anti-D needed for this pregnancy; (5) ANTI-D after any sensitising event (bleeding, trauma, miscarriage, amnio). PROTECTS future pregnancies. /calculators/anti-d-dosing for full detail.
What if I'm Rh-positive?
NO anti-D pathway. Standard antenatal care. BABY'S Rh status doesn't matter for you. ABO incompatibility can occasionally cause mild newborn jaundice but rarely serious.
Can I predict baby's blood type from parents?
PARTIALLY. ABO: depends on both parents. RH: if BOTH Rh-negative, baby will be Rh-NEGATIVE. If EITHER parent Rh-positive, baby COULD be Rh-positive (especially likely if dad Rh-pos). NOT GUARANTEED — depends on which alleles passed. SOMETIMES SURPRISING combinations (e.g. O+ × A+ can produce O, A, depending on parents' genes). NIPT/cffDNA more reliable than calculator.
What blood types can what?
ABO COMBINATIONS: O × O → O only. A × A → A or O. B × B → B or O. AB × anything → many possibilities. O × A → O or A. O × B → O or B. Most combinations possible depending on whether parent is homozygous (AA) or heterozygous (AO). KARYOTYPE / DNA testing definitive but rarely needed in pregnancy.
What's ABO incompatibility?
When mum is O and baby is A or B. MUM'S ANTI-A or ANTI-B antibodies (natural in O blood) cross placenta + attack baby's red cells. USUALLY MILDER than Rh disease. PRESENTATION: NEONATAL JAUNDICE in first 24 hours; sometimes anaemia. TREATMENT: PHOTOTHERAPY usually sufficient; rarely exchange transfusion. NO ANTENATAL anti-D equivalent for ABO; managed reactively. ALL O-blood mothers monitored for newborn jaundice carefully.
What other antibodies matter?
BESIDES ANTI-D (Rh disease): ANTI-c, ANTI-Kell, ANTI-Duffy, ANTI-Kidd, ANTI-MNS others. RARE but serious. ANTIBODY SCREEN at booking + 28 weeks detects. If positive: identify antibody; titer; monitor; fetal MCA Doppler for anaemia; possible intrauterine transfusion. ANTI-KELL particularly aggressive — severe anaemia at lower titers than anti-D. SPECIALIST fetal medicine care.
Should I know my partner's blood type?
USEFUL but not essential. IF YOU'RE RH-NEGATIVE: partner's Rh type helps. RH-NEG dad + RH-NEG mum = Rh-neg baby (no anti-D). RH-POS dad: baby could be Rh-pos (anti-D pathway). cffDNA TEST avoids need to know — tests baby's Rh from mum's blood at 11-13 wk. PARTNER blood type rarely affects ABO management.
Why are Rh-negative women rarer in some ethnicities?
Rh blood type DISTRIBUTION varies by ancestry. CAUCASIAN (European): ~15% Rh-negative. BLACK / SUB-SAHARAN AFRICAN: ~5-8%. EAST ASIAN / CHINESE: <1%. INDIGENOUS American / Native populations: very rare. BASQUE region (Spain/France): ~25% — highest. INDIAN / South Asian: ~5%. ANTI-D screening universal; affects all women equally.
Can blood type change?
NO. Your blood type is GENETIC — determined at conception, set for life. RH ANTIBODIES can develop (if exposed without prevention) — once developed, persistent. SOME treatments (e.g. bone marrow transplant) can change blood type if from different donor type — exceedingly rare scenario. PREGNANCY itself doesn't change your blood type.
What about COVID / vaccines affecting blood?
NO impact on blood type. COVID vaccines: SAFE in pregnancy + breastfeeding; recommended. Don't affect Rh status or antibody screening. ROUTINE blood tests in pregnancy unchanged.
Will I bleed more if I'm O-negative?
BLOOD TYPE doesn't affect clotting normally. RHESUS NEGATIVE specifically: no increased bleeding risk. ABO TYPE: some research suggests Type O has slightly LOWER von Willebrand factor (clotting protein) — may have slightly more bleeding tendency than other types, but clinically usually irrelevant. POSTPARTUM HAEMORRHAGE risk affected by many other factors more than blood type.
Can I receive any blood transfusion if needed in pregnancy?
STANDARDLY: blood matched to your type. O-NEGATIVE = 'universal donor' (can give to anyone but receives only O-neg in non-emergency). AB-POSITIVE = 'universal recipient' (can receive any blood type). IN EMERGENCY: O-NEGATIVE used while typing pending. CROSS-MATCH done before any transfusion. PREGNANCY OUTCOMES: standard transfusion safe; antibodies developed in pregnancy considered for future.
How does this relate to other calculators on BumpBites?
Companion: /calculators/anti-d-dosing for full Rh management; /calculators/newborn-bilirubin (ABO/Rh causes); /calculators/kleihauer-betke (quantify fetal bleed); /calculators/recurrent-miscarriage; /calculators/methotrexate-ectopic (anti-D given).