Trimesters are the three divisions of pregnancy, each lasting approximately three months and marking key stages in fetal development and maternal changes. The first trimester (weeks 1–12) involves early fetal growth and the development of major organs. The second trimester (weeks 13–26) is often marked by noticeable fetal movement and continued organ maturation. The third trimester (weeks 27–40) includes rapid growth, final development, and preparation for birth. Understanding trimesters helps guide prenatal care, screening, and monitoring throughout pregnancy.