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Milestones of Prenatal development


1st week of gestation : fertilization and implantation , beginning of embryonic period.
2nd week of gestation : endoderm and ectoderm appear ( bilaminar embryo ).
3rd week of gestation : first missed menstrual period, mesoderm appears ( trilaminar embryo ), somites begin to form.
4th week of gestation : neural folds fuse, folding of embryo into human like shape, arm and leg buds appear , crown-rump length is 4 to 5 mm .
5th week of gestation : lens placodes,primitive mouth,digital rays on hands.
6th week of gestation : primitive nose , philtrum ,primary palate , crown-rump length 21 – 23 mm
7th week of gestation : eyelids begin
8th week of gestation : ovaries and testes distinguishable
9th week of gestation : fetal period begins, crown-rump length is 5 cms, weight is 9 grams .
10th week of gestation : external genitalia distinguishable
20th week of gestation : usual lower limit of viability ,weight is 460 grams , length is 19 cms
28th week of gestation : eyes open , fetus turns head down , weight is 1000 grams
38th week of gestation : term.

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