The reference provided deals with red blood cell (RBC) changes during pregnancy but does not define "RCB." Therefore, without further context, "RCB" in the context of pregnancy is ambiguous. It could potentially refer to several things, requiring clarification. It is likely a typo, acronym, or abbreviation that cannot be accurately identified based solely on the reference material.
Therefore, without more information or context, I cannot definitively define "RCB" in pregnancy.
