The first trimester is the earliest phase of pregnancy. It spans from week 1 to the end of week 12. During this time, your baby grows faster than at any other time. By 6 weeks, a heartbeat can usually be detected and by the end of week 12, your baby's bones, muscles, and all of the organs will have formed.

The second trimester spans from week 13 to the end of week 26. During this time, your baby continues to grow and develop almost all of the features they'll have at birth. Many women find that symptoms like nausea and fatigue improve during this trimester, but other symptoms may continue or begin.

The third trimester spans from week 27 to the end of the pregnancy (around week 40). During this time, your baby will gain a lot of weight and prepare for birth. You may find that symptoms like heartburn, backache, and fatigue become worse as your baby grows larger.