( ( The increase ) ( ( ( is ( secondary ( to ( ( a ( gradual decrease ) ) ( in ( vessel resistance ) ) ) ) ) ) ( to ( ( blood flow ) ( throughout ( the pregnancy ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN increase)) (VP (VBZ is) (ADJP (JJ secondary) (PP (TO to) (NP (NP (DT a) (JJ gradual) (NN decrease)) (PP (IN in) (NP (NN vessel) (NN resistance)))))) (PP (TO to) (NP (NP (NN blood) (NN flow)) (PP (IN throughout) (NP (DT the) (NN pregnancy)))))) (. .)))
The increase is secondary to a gradual decrease in vessel resistance to blood flow throughout the pregnancy.
(ROOT (S (NP (NNP Blood)) (VP (VBP flow) (VP (VB decrease) (SBAR (WHADVP (WRB when)) (S (NP (NN blood) (NNS vessels)) (VP (VBP constrict)))))) (. .)))