Child Health A-Z

Pregnancy

Picture of expectant mother holding her belly

A pregnancy is divided into three phases, called trimesters. Each trimester has its own significant milestones. The first trimester is the most fragile period, during which all major organs and systems are formed. Most birth defects and miscarriages occur during the first trimester. During the second and third trimester, the fetus is fully formed and grows and matures rapidly. The trimesters are divided as follows:

first trimester: 0 - 12 weeks
second trimester: 12 - 24 weeks
third trimester: 24 - 40 weeks

(However, some authorities use the 42 weeks method divided by 3 trimesters with the 1st trimester, 0 - 13 weeks; the 2nd trimester, 14 - 28 weeks; and the 3rd trimester, 29 - 42 weeks.)

Listed in the directory below, you will find additional information regarding the three phases of pregnancy, for which we have provided a brief overview.

Last Update
February 3, 2008