Germinal stage weeks 0-2 associated with zygote formation, cell division and zygote attachment to the uterine wall.
Embryonic stage weeks 3-8 with organ formation and teratogen sensitivity.
Fetal stage-week 9-birth associated with rapid fetal growth, sex organ formation and organ system function.
The brain develops most quickly in the first 1,000 days of life, from the start of pregnancy to the child’s second birthday.