B positive and B negative parents
Possible baby blood types: O+, O-, B+, B-. Not possible: A+, A-, AB+, AB-.
| Child | Range | Typical |
|---|---|---|
| 0% – 25% | 15.7% | |
| 0% – 12.5% | 6.3% | |
| Not possible | — | |
| Not possible | — | |
| 37.5% – 100% | 55.8% | |
| 0% – 50% | 22.3% | |
| Not possible | — | |
| Not possible | — |
Range = lowest to highest chance across the genotypes each parent could carry. Typical = weighted by common allele frequencies. Try other inputs in the blood type calculator.
Why these results
A B positive parent carries ABO genes BB or BO and Rh genes DD or Dd. A B negative parent carries BB or BO and dd. Each passes one ABO gene and one Rh gene to the child at random.
ABO: every genotype pairing
| Parent 1 | Parent 2 | Child’s ABO group | Share of couples |
|---|---|---|---|
| BB | BB | B 100% | 0.4% |
| BB | BO | B 100% | 6% |
| BO | BB | B 100% | 6% |
| BO | BO | O 25% · B 75% | 87.6% |
Rh factor
| Parent 1 | Parent 2 | Child |
|---|---|---|
| DD | dd | Rh+ 100% |
| Dd | dd | Rh+ 50% · Rh− 50% |
Step through any pairing on the blood type Punnett square.
Pregnancy and Rh
If the mother is the B- parent, the baby could be Rh positive, so she is usually offered anti-D (RhoGAM) around 28 weeks and again after birth if the baby is Rh positive. If the mother is the Rh-positive parent, no anti-D is needed. See the Rh factor guide.
Can these parents give each other blood?
B positive can receive red cells from O+, O-, B+, B-; B negative can receive from O-, B-. Full rules are on the blood type compatibility chart.
Frequently asked questions
What blood type will a baby of B+ and B- parents have?
The child can be O+, O-, B+, B-. Under normal inheritance the child cannot be A+, A-, AB+, AB-. The most likely single type, using typical gene frequencies, is B+ (about 55.8%).
Can B+ and B- parents have a O+ child?
Yes. The chance is 0% – 25%, depending on the hidden genes each parent carries (about 15.7% with typical gene frequencies).
Can B+ and B- parents have a O- child?
Yes. The chance is 0% – 12.5%, depending on the hidden genes each parent carries (about 6.3% with typical gene frequencies).
Can B+ and B- parents have a B+ child?
Yes. The chance is 37.5% – 100%, depending on the hidden genes each parent carries (about 55.8% with typical gene frequencies).
Can B+ and B- parents have a B- child?
Yes. The chance is 0% – 50%, depending on the hidden genes each parent carries (about 22.3% with typical gene frequencies).
Does it matter which parent is the mother?
For the baby’s blood type, no. For pregnancy care, yes: if the mother is the Rh-negative parent and the baby could be Rh positive, she is usually offered anti-D (RhoGAM).