( 12th ( ( ( ( ( ( WEEK ( ( The baby ) ( ( wakes and ) sleeps ) ) ) and ) exercises ) , ) ( ( ( moving about ) and ) ( ( breathing ( amniotic fluid ) ) ( to ( strengthen ( his ( developing ( respiratory system ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP 12th)) (VP (VP (VBD WEEK) (SBAR (S (NP (DT The) (NN baby)) (VP (VP (VBZ wakes)) (CC and) (VP (VBZ sleeps)))))) (CC and) (VP (VBZ exercises)) (, ,) (S (VP (VP (VBG moving) (IN about)) (CC and) (VP (VBG breathing) (NP (JJ amniotic) (NN fluid)) (S (VP (TO to) (VP (VB strengthen) (NP (PRP$ his) (VBG developing) (NN respiratory) (NN system))))))))) (. .)))
12th WEEK The baby wakes and sleeps and exercises, moving about and breathing amniotic fluid to strengthen his developing respiratory system.
(ROOT (S (NP (NP (DT The) (NN development)) (PP (IN of) (NP (NP (DT the) (JJ respiratory) (NN system)) (PP (IN in) (NP (DT the) (NN fetus)))))) (VP (VBZ begins) (PP (IN at) (NP (QP (RB about) (CD 4)) (NNS weeks)))) (. .)))
The development of the respiratory system in the fetus begins at about 4 weeks.