The first trimester covers weeks 1 through 12, encompassing the initial stages of pregnancy. During this period, the fertilized egg implants in the uterus, cell division accelerates, and major organs and systems begin to form. Common symptoms for the pregnant individual may include morning sickness, fatigue, and breast tenderness. Routine prenatal visits typically begin in the first trimester to confirm pregnancy, estimate due dates, and screen for chromosomal abnormalities through tests like the nuchal translucency scan or first-trimester combined screening.
The second trimester, spanning weeks 13 to 26, is often considered the most comfortable phase of pregnancy. Physical symptoms like nausea and fatigue may subside, and the fetus undergoes rapid growth, developing muscles, bones, and senses. Ultrasound imaging during this trimester can provide detailed images of the baby’s anatomy, allowing for further assessment of development. Some healthcare providers may recommend additional screenings, such as the second-trimester anomaly scan, to check for structural abnormalities.
The third trimester, from week 27 to birth, focuses on preparing for labor and delivery. The fetus continues to grow, gaining weight and refining motor skills, while the pregnant individual may experience increased discomfort due to physical changes. Regular prenatal visits monitor fetal heart rate, growth, and positioning, and discussions about birth plans, pain management, and potential complications become more prominent. Toward the end of this trimester, healthcare providers may recommend tests like group B streptococcus screening or glucose tolerance tests to ensure both mother and baby are healthy.
Trimesterden is not limited to human pregnancy but is also used in veterinary medicine and reproductive health research to standardize developmental tracking across species. Understanding the progression through each trimester helps expectant parents and healthcare teams anticipate milestones and address any concerns promptly.