Blood group of the newborn: how he inherits it

Children inherit blood type A, B, AB or 0 from both their father and mother, and their combination determines their blood type.
Starting from the basics, i.e. seeing what blood groups are, let’s find out how and when they are compatible. Finally we will talk about inheritance.

What are blood groups

Blood groups are a hereditary component that is identified thanks to the antigens present on the surface of red blood cells.

There are four main blood groups: A – AB – B – O. AB positive is considered the universal recipient. O negative is considered the universal donor.

Frequency of blood group (in the Italian population)

According to data from the Association of Italian Blood Volunteers (AVIS), in Italy, the

  • 40% of people have group 0,
  • 36% have blood group A,
  • 17% have blood group B,
  • 7% have blood type AB.

Blood group compatibility

As we have already mentioned, the blood group (A, B, AB or 0) depends on the presence or absence of the A and B antigens on the red blood cells:

  • blood group A has only antigen A,
  • blood type B has only B antigen,
  • blood type AB has both A and B antigens,
  • blood type O has neither A nor B antigen.

The human being, starting from 6 months of age, therefore when he is still a newborn, develops antibodies against the antigens that are missing in his red blood cells.

For example, an infant with blood type A will develop anti-B antibodies, and an infant with blood type B will develop anti-A antibodies.
Consequently, a human being (infant or adult) with blood type A cannot receive blood B because his body’s anti-B antibodies will fight the B antigens of blood B.

In the following table we summarize the compatible combinations of blood groups.

GROUP YOU CAN DONATE BLOOD TO: YOU CAN RECEIVE BLOOD FROM:
A+ A+, AB+ A+, A-, 0+, 0-
A- A+, A-, AB+, AB- A-, 0-,
B+ B+, B-, AB+, AB- B+, B-, 0+, 0-
B- B+, B-, AB+, AB- B-, 0-
0+ 0+, A+, B+, AB+ 0+, 0-
0- Everyone 0-
AB+ AB+ Everyone
AB- AB+, AB- AB-, A-, B-, 0-

Blood type inheritance from parents

All human beings, starting from the neonatal stage, have a blood group (A, B, AB or O) and a Rh factor (positive or negative).

Just like eye or hair color, our blood type is inherited from parents.

Each biological parent donates one of the two genes to their child. Genes A and B are dominant and gene O is recessive. For example,

  • if an O gene is paired with an A gene, the blood type will be A.
  • an O blood parent with 2 O genes and an A blood parent with 2 A genes will have a blood type A child with one A gene and one O gene.

In the table below we summarize the hereditary combinations of blood groups.

Genes Parents aa BB VIA OO A BO
aa aa VIA AA, AB A AA, AO AB, AO
BB VIA BB AB, BB BO AB, BO BB, BO
VIA AA, AB AB, BB AA, BB, AB AO, BO AA, AO, BO, AB BB, BO, AB, AO
OO A BO AO, BO OO AO, OO BO, OO
A AA, AO AB, BO AA, AB, AO, BO AO, OO AA, AO, OO AO, BO, AB, OO
BO AO, AB BB, BO AB, AO, BB, BO BO, OO AB, AO, BO, OO BB, BO, OO

As discussed above:

AA = Blood group A
AO = Blood group A
BB = Blood group B
BO = Blood group B
OO = Blood group 0
AB = Blood group AB

The Rh factor

Rh factor is (simply) a protein found on the lining of red blood cells. If a person’s red blood cells have this protein, they are Rh positive. While if the blood cells do not have this protein, it is Rh negative.

Inheritance of the Rh factor from parents

Just as we inherit blood type, we also inherited a rhesus factor gene from each parent. The Rh-positive gene is the dominant gene when paired with a Rh-negative gene.

From this we can easily deduce the results of the different combinations of genes, which we have summarized in the following table.

Katherine Johnson, M.D., is a board-certified obstetrician-gynecologist with clinical expertise in general obstetrics and gynecology, family planning, women’s health, and gynecology.

She is affiliated with the Obstetrics and Gynecology division at an undisclosed healthcare institution and the online platform, Maternicity.com.

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