Pregnancy typically lasts about 40 weeks, counted from the first day of your last menstrual period (LMP). This 40-week journey is divided into three distinct trimesters—first, second, and third—each marking unique stages in fetal development and maternal changes. From the rapid organ formation in the first trimester to growth and preparation for birth in the third, knowing what happens week by week helps you stay informed and prepared. Our Pregnancy Calculator and Due Date Calculator provide personalized tracking tools to guide you through this exciting journey.
First Trimester (Weeks 1-13): Foundations of Life and Early Changes
The first trimester is critical for organ formation and lays the foundation for your baby’s development. During these weeks:
- Baby develops from a fertilized egg to a fetus about the size of a peach.
- Common symptoms include nausea, fatigue, breast tenderness, and frequent urination, with many women experiencing the peak of morning sickness between weeks 6-9.
- The risk of miscarriage is highest in this period.
- You’ll likely have your first prenatal appointment during this trimester to confirm pregnancy and initial baby growth via ultrasound.
Second Trimester (Weeks 14-27): Growth and Increased Energy
Known as the “honeymoon phase” of pregnancy, the second trimester usually brings relief from early pregnancy symptoms. Key highlights:
- The baby grows rapidly, tripling in length and gaining weight.
- You may begin to feel the baby’s first movements (quickening) around weeks 16-20.
- Many women experience an energy boost and visible baby bump.
- Important scans include the anatomy ultrasound to check fetal development and screen for anomalies.
Lifestyle tips focus on balanced nutrition and moderate exercise to support this phase of growth.
Third Trimester (Weeks 28-40): Preparation for Birth
In the final trimester, your baby gains most of its weight and prepares for birth. Expect:
- Increased physical discomfort such as back pain, swelling, and frequent urination.
- Baby’s lungs mature, and the head usually “engages” in the pelvis.
- You may experience Braxton Hicks contractions and notice the loss of the mucus plug signaling labor readiness.
- Prenatal visits become more frequent to monitor fetal position and maternal health.
Planning for labor and packing your hospital bag can start during this trimester.
Trimester Comparison: What to Expect
| Trimester | Baby’s Focus | Mom’s Common Symptoms | Important Tests/Scans | Risk Factors |
|---|---|---|---|---|
| First (1-13) | Organ formation | Nausea, fatigue, breast changes | Dating ultrasound, blood tests | Highest miscarriage risk |
| Second (14-27) | Rapid growth | Energy increase, baby movements | Anatomy scan, glucose screening | Anomaly detection |
| Third (28-40) | Fat gain, lung maturation | Discomfort, nesting, contractions | Non-stress tests, weekly visits | Preterm labor, delivery planning |
Why Using Pregnancy Week-by-Week Tracking Matters
Weekly tracking helps expectant mothers understand symptoms, fetal growth, and when to expect key milestones—reducing anxiety and optimizing health. Our Pregnancy Calculator gives tailored weekly info including baby size, symptom checklists, and upcoming tests or appointments, ensuring you never miss an important moment.
Tips for a Healthy Pregnancy Across Trimesters
- Eat nutritious foods rich in folic acid, iron, and calcium.
- Stay active with pregnancy-safe exercises, such as walking or prenatal yoga.
- Prioritize rest and manage stress for emotional well-being.
- Attend all prenatal appointments for timely screenings and guidance.
- Seek emergency care for warning signs like heavy bleeding, severe pain, or reduced fetal movement.
FAQs About Pregnancy Trimesters
How long is each trimester? Roughly 13 weeks each, though exact week boundaries vary slightly.
When is the baby viable? Survival rates increase significantly after 24 weeks gestation.
What symptoms are different by trimester? Nausea is common early, energy surges mid-pregnancy, and physical discomfort rises late.
Begin Your Pregnancy Journey Confidently
Enter your due date or last menstrual period in our Pregnancy Calculator to receive your personalized week-by-week pregnancy guide. Confirm and adjust your due date anytime with our Due Date Calculator. Share your current week or questions below for community support and expert tips.
This comprehensive trimester and weekly guide empowers you with knowledge to enjoy a healthy and informed pregnancy from start to finish.