Can two o blood types make a b negative baby?

O baby: An o mom and an o dad will make an o baby, the old-fashioned way. It's possible that they may have babies of other blood types through other means or activities.

No: This genetic combination would only produce a baby with an o blood type.Before jumping to conclusions check the parents blood type. Lots of people get these wrong.

Rarely: There are rare exceptions to simple mendelian inheritance of the ABO groups. There are weak alleles, the Bombay phenotype which masks B, and a few others. There are also lab errors. Don't jump to any conclusions.