Weeks 1 - 4- one month
5 - 8 - two months
9-13 three months
14- 17- four months
18 - 21- five
months
22 - 26- six
months
27 - 30- seven
months
31 - 35- eight
months
36 - 40-
nine months
One to three months first trimester
Four to six moths second trimester
Seven to nine months third trimester
This is from the dr office.