A) 4th week
B) 3rd week
C) 6th week
D) 8th week
Correct Answer: A
Solution :
Week 1: Fertilization, cleavage to form a blastocyst 4-5 days after fertilization. More than 100 cells. Implantation 6-9 days after fertilization. Week 2: The three basic layers of the embryo develop, namely ectoderm, mesoderm and endoderm. No research allowed on human embryos beyond this stage. Week 3: Woman will not have a period. This may be the first sign that she is pregnant. Beginnings of the backbone. Neural tube develops, the beginning of the brain and spinal cord (first organs). Embryo about 2 mm long. Week 4: Heart, blood vessels, blood and gut start forming. Umbilical cord developing. Embryo about 5 mm long. Week 5: Brain developing, limb buds, small swellings which are the beginnings of the arms and legs. Heart is a large tube and starts to beat, pumping blood. This can be seen on an ultrasound scan. Embryo about 8 mm long. Week 6: Eyes and ears start to form. Week 7: All major internal organs developing. Face forming. Eyes have some colour. Mouth and tongue. Beginnings of hands and feet. Foetus is 17 mm long. Week 12: Foetus fully formed, with all organs, muscles, bones, toes and fingers. Sex organs well developed. Fetus is moving. For the rest of the gestation period, it is mainly growing in size. Fetus is 56 mm long from head to bottom. Pregnancy may be beginning to show. Week 20: Hair begin to grow, including eyebrows and eyelashes. Fingerprints developed. Fingernails and toe nails growing. Firm hand grip. Between 16 and 20 weeks baby usually felt moving for first time. Baby is 160 mm long from head to bottom. Week 24: Eyelids open, legal limit for abortion in most circumstances. Week 26: Has a good chance of survival if born prematurely. Week 28: Baby moving vigorously, responds to touch and loud noises. Swallowing amniotic fluid and urinating. Week 30: Usually lying head down ready for birth. Baby is 240 mm from head to bottom. 40 weeks (9 months): Birth.
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