( ( ( A ( ( mother and ) fetus ) ) ( may ( have ( incompatible ( blood types ) ) ) ) ) ( , ( ( the ( most common ) ) ( ( is ( Rh incompatibility ) ) . ) ) ) )
(ROOT (S (S (NP (DT A) (NN mother) (CC and) (NN fetus)) (VP (MD may) (VP (VB have) (NP (JJ incompatible) (NN blood) (NNS types))))) (, ,) (NP (DT the) (RBS most) (JJ common)) (VP (VBZ is) (VP (VBN Rh) (ADVP (RB incompatibility)))) (. .)))
A mother and fetus may have incompatible blood types, the most common is Rh incompatibility.
(ROOT (S (NP (NNP Rh)) (VP (VBZ is) (NP (NP (DT the) (JJ common) (NN abbreviation)) (PP (IN for) (S (VP (VBG noting) (NP (DT the) (JJ rhesus) (NN blood) (NN type))))))) (. .)))