Human Embryonic and Fetal Development

Key Questions

  • Answer:

    In humans , the gestation period is usually of 9 months i.e 266 days /38 weeks (+,- 7 days --depending upon the amount of Progesterone).


    It is divided into three trimesters ;

    Trimester 1
    First week -Implantation takes place ( at he 7th day of fertilisation )
    Second week - Germ layers are formed
    Third week - Suppressed menstrual cycle indicates pregnancy (not confirmatory)
    Fourth week - Blood vessels are formed . Heart is formed and brain starts developing .

    Trimester 2
    Fifth week - Heart starts pumping the blood . LUB- DUB sound could be heard during ultrasound .
    Sixth week- Internal organs are formed . Mouth , face are formed . Gonads are formed.
    Seventh week - External , internal ear is formed
    Eighth week - Eyelids are formed , but closed .

    Trimester 3
    Complete organ formation takes place .