The 40 or so weeks of pregnancy are divided into three stages or trimesters that are each 12 - 13 weeks long. Each group of weeks brings dramatic changes to the developing baby and physical changes and symptoms for Mom. During the first trimester, weeks 1 – 12, hormone changes bring an end to your period, lack of energy, increase in urination, heartburn and upset stomach, tender breasts, cravings or distaste for certain foods, moodiness, and constipation. At twelve weeks, an ultrasound can sometimes determine the gender of the fetus. Some women report all, some or none of these symptoms. Each woman and each pregnancy are different.
During the second trimester, many women see their morning sickness and tiredness disappear. Normal changes to Mom’s body include enlarged belly, back ache, darkening of skin around the nipples, dark patches of skin on the face, and swelling in the face, ankles, and fingers.
https://www.empowher.com/pregnancy/content/overview-stages-pregnancy