( ( These studies ) ( ( require ( ( ( a sample ) ( of fetally ) ) ( derived ( tissue ( that ( can ( be ( obtained ( either ( ( ( by ( ( ( ( ( chorionic ( villus sampling ) ) ( -LRB- ( CVS -RRB- ) ) ) , ) ( which ( can ( be ( ( performed ( as early ) ) ( as ( ( the ( ninth week ) ) ( of pregnancy ) ) ) ) ) ) ) ) , ) ) or ) ( by ( ( amniocentesis , ) ( which ( is ( ( performed ( at ( ( approximately 16 ) weeks ) ) ) ( after ( the ( last ( menstrual period ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT These) (NNS studies)) (VP (VBP require) (SBAR (S (NP (NP (DT a) (NN sample)) (PP (IN of) (NP (NN fetally)))) (VP (VBD derived) (NP (NP (NN tissue)) (SBAR (WHNP (WDT that)) (S (VP (MD can) (VP (VB be) (VP (VBN obtained) (PP (CC either) (PP (IN by) (NP (NP (NP (JJ chorionic) (NNS villus) (NN sampling)) (PRN (-LRB- -LRB-) (NP (NNP CVS)) (-RRB- -RRB-))) (, ,) (SBAR (WHNP (WDT which)) (S (VP (MD can) (VP (VB be) (VP (VBN performed) (ADVP (RB as) (RB early)) (PP (IN as) (NP (NP (DT the) (JJ ninth) (NN week)) (PP (IN of) (NP (NN pregnancy)))))))))) (, ,))) (CC or) (PP (IN by) (NP (NP (NNS amniocentesis)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ is) (VP (VBN performed) (PP (IN at) (NP (QP (RB approximately) (CD 16)) (NNS weeks))) (PP (IN after) (NP (DT the) (JJ last) (JJ menstrual) (NN period)))))))))))))))))))) (. .)))
These studies require a sample of fetally derived tissue that can be obtained either by chorionic villus sampling (CVS), which can be performed as early as the ninth week of pregnancy, or by amniocentesis, which is performed at approximately 16 weeks after the last menstrual period.
(ROOT (S (NP (DT The) (JJ fetal) (NN period)) (VP (VBZ lasts) (NP (NP (QP (RB approximately) (CD 30)) (NNS weeks)) (NP (NNS weeks)))) (. .)))