( ( In humans ) ( , ( this ( ( occurs ( at ( ( ( ( 21 to ) 28 ) days ) ( of ( ( fetal age ) ( which ( is ( ( ( about 6 ) weeks ) ( after ( the ( last ( menstrual ( period ( .14 12 ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (NNS humans))) (, ,) (NP (DT this)) (VP (VBZ occurs) (PP (IN at) (NP (NP (QP (CD 21) (TO to) (CD 28)) (NNS days)) (PP (IN of) (NP (NP (JJ fetal) (NN age)) (SBAR (WHNP (WDT which)) (S (VP (VBZ is) (NP (NP (QP (RB about) (CD 6)) (NNS weeks)) (PP (IN after) (NP (DT the) (JJ last) (JJ menstrual) (NN period) (QP (CD .14) (CD 12))))))))))))) (. .)))
In humans, this occurs at 21 to 28 days of fetal age which is about 6 weeks after the last menstrual period.14 12.
(ROOT (S (NP (DT The) (JJ fetal) (NN period)) (VP (VBZ lasts) (NP (NP (QP (RB approximately) (CD 30)) (NNS weeks)) (NP (NNS weeks)))) (. .)))