trimesters

• month old human embryo is 7mm (0.28), somite stage of frog embryo
• fetus - 9 weeks after fertilization
• fetus is 5.5 cm (2.2in) size first trimester
• somites will develop into segmental muscles and bones of backs and ribs
• sex of fetus and shape is evident after 1st trimester
• second trimester fetus is about 6 cm (2.4 inches)
• placenta secretes progresterone but stops secreting HCG and corpus luteum deteriorates
• 20 weeks 19 cm (7.6in) half a kilogram (1lb)
• 2nd trimester features start to be identified such as face, fingernails, hair, otehrs
• second trimester, fetal position and heartbeat is detected and eyes and teeth will form