It is divided into three trimesters ;
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 .
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 .
Complete organ formation takes place .