Blood Group: ABO
Common: Yes, especially among blacks. 62.7% of black type O people have anti-B
Causes HDN: Yes
Critical Titer: 1:16
One of the important things to note is that there is a difference in the severity of HDN based on race. HDN due to anti-A or anti-B is more severe in blacks and latinos than in whites [2, 3]. It is possible to have both anti-A and anti-B at the same time . It is especially important that black infants are not discharged from the hospital prematurely and without proper follow up when ABO incompatibility is suspected. It has been suggested that a 6 hour bilirubin can determine the risk for significant hyperbilirubinemia (4 mg/dL) or severe HDN (6 mg/dL) due to ABO incompatibility .
ABO HDN remains the most frequent cause of severe and early jaundice in newborns . Treatments include exchange transfusion and IVIG in addition to phototherapy. Exchange transfusion can lead to a 44.03% reduction in indirect bilirubin . IVIG can reduce the need for exchange transfusion [4, 5]. One study suggests that maternal titers >1:512 can be good predictors of the need for IVIG and exchange transfusion , while another study says that titers aren’t useful in predicting the need for exchange transfusion .
In general HDN from Anti-B is viewed as being more severe than anti-A. This is because severe HDN due to anti-B is seen more frequently than severe HDN due to anti-A, however anti-A can cause severe HDN too. . Another study said that anti-A and anti-B occur with almost the same frequency and there is no difference in severity .
There are multiple reports of severe HDN due to anti-B [12, 13, 14, 15]. While rare, anti-B can affect baby in utero and is capable of causing hydrops  and fetal distress requiring emergency c section [12, 13]. Anti-B can also affect baby after birth and cause severe anemia within hours [14, 15].
14 - https://www.ncbi.nlm.nih.gov/pubmed/1571313016 - https://www.ncbi.nlm.nih.gov/books/NBK2267/