Pregnancy Week by Week: What to Expect Each Trimester

Pregnancy is a remarkable 40-week journey filled with rapid changes for both mother and baby. Knowing what to expect each trimester helps you prepare, stay healthy, and recognize when to contact your healthcare provider. Here is an overview of the major milestones.

First Trimester (Weeks 1–12)

The first trimester is when the most critical development occurs, even though your baby is still tiny by the end of this period.

• Weeks 1–4: Fertilization occurs, and the embryo implants in the uterine wall. The placenta begins forming. Most women do not yet know they are pregnant.
• Weeks 5–8: The heart begins beating. Facial features, limb buds, and major organs start developing. Morning sickness, fatigue, and breast tenderness are common.
• Weeks 9–12: All major organs and body systems are in place. Fingers and toes form. By week 12, the baby is about 2.5 inches long and weighs roughly half an ounce. The risk of miscarriage drops significantly after week 12.

Key appointments: Your first prenatal visit (usually week 8–10) will confirm the pregnancy and estimate your due date. Genetic screening tests may be offered.

Second Trimester (Weeks 13–26)

Often called the "golden trimester" because morning sickness typically subsides and energy levels improve.

• Weeks 13–16: The baby begins moving, though you may not feel it yet. Fingerprints develop. Gender can often be determined.
• Weeks 17–20: You will likely feel the first movements (quickening). The anatomy scan at week 18–20 checks the baby's organs, measurements, and position.
• Weeks 21–26: The baby can hear sounds and responds to light. Lungs are developing but not yet mature. By week 26, the baby weighs about 2 pounds.

Important: Glucose screening for gestational diabetes is typically done between weeks 24 and 28.

Third Trimester (Weeks 27–40)

The final stretch focuses on growth, lung maturation, and preparation for delivery.

• Weeks 27–32: The baby gains weight rapidly. Brain development accelerates. You may experience Braxton Hicks contractions, back pain, and shortness of breath.
• Weeks 33–36: The baby moves into a head-down position in preparation for birth. Lungs continue maturing. Prenatal visits increase to every two weeks or weekly.
• Weeks 37–40: The baby is considered full term at 39 weeks. Average birth weight is 6 to 9 pounds. Many babies arrive between weeks 38 and 42.

Calculating Your Due Date

Due dates are calculated as 280 days (40 weeks) from the first day of your last menstrual period. Keep in mind that only about 5% of babies arrive on their exact due date — most arrive within a two-week window on either side.

Track Your Pregnancy

Use our pregnancy due date calculator to determine your estimated due date, current week, and trimester based on your last menstrual period or conception date.

Every pregnancy is unique, so always discuss your specific symptoms and concerns with your healthcare provider. This guide provides a general roadmap, but your doctor or midwife is your best resource for personalized care.