How does a human fetus change during development lab answer key?

It starts when the egg is fertilized.

 After fertilization, the blastocyst begins to produce pregnancy hormones which tell the ovary to stop releasing eggs. At four weeks then the cell becomes an embryo.
 At thirteen weeks the first trimester is over then goes to the second trimester from week fourteen. It is in this trimester that all body parts of the baby are formed including the intestines.
 At week 27 the second trimester ends. Now it is in the third trimester where a person prepares for a childbirth class, baby registry, and doctor for your baby. At 39 weeks the baby is considered full term and the baby all physical development is complete.
The pregnancy may exceed only two weeks which is considered as the late-term.