During pregnancy, you when the baby had just began developing, Why does the mother not notice the signs of pregnancy until 7 to 14 days are up? And what are some differences in pregnancies between two

During pregnancy, you when the baby had just began developing, Why does the mother not notice the signs of pregnancy until 7 to 14 days are up? And what are some differences in pregnancies between two seperate women? How can you have a healthy pregnancy?