Pregnancy Week by Week: What to Expect Each Trimester

From a tiny cluster of cells to a fully formed baby in just 40 weeks — pregnancy is an extraordinary journey. Whether you just found out or you're planning ahead, this guide walks you through what's happening to your body and your baby each trimester, the key milestones to expect, and the appointments you'll need along the way.

First Trimester (Weeks 1–12)

The first trimester is when the most critical development happens. By week 12, all major organs and systems have begun forming.

See also: Pregnancy Sleep Positions: How to Sleep Safely Each Trimester and Postpartum Recovery: What to Expect Week by Week.

Weeks 1–4: Conception & Implantation

Fertilization occurs around week 2. By week 4, the embryo implants in the uterine wall and the placenta begins forming. Most women don't know they're pregnant yet.

Weeks 5–8: Rapid Development

The heart starts beating (week 5–6). Arms, legs, fingers, and toes begin forming. The neural tube (future brain and spinal cord) closes. Morning sickness typically peaks during this period.

Weeks 9–12: Fetus Stage Begins

At week 9, the embryo officially becomes a fetus. Facial features develop, bones begin hardening, and genitals start differentiating. By week 12, the risk of miscarriage drops significantly.

Second Trimester (Weeks 13–27)

Often called the "golden trimester" — nausea fades, energy returns, and you start showing. Many women feel their best during this period.

Weeks 13–16: Energy Returns

Morning sickness usually subsides. Your bump starts showing. Baby can hear sounds and begins making facial expressions. The anatomy scan is typically scheduled around week 20.

Weeks 17–20: First Kicks

You may feel "quickening" — baby's first movements, often described as flutters or bubbles. First-time moms usually notice them around weeks 18–22. The 20-week anatomy scan checks all organs and can reveal the sex.

Weeks 21–27: Rapid Growth

Baby gains weight quickly. Lungs develop surfactant (needed for breathing). Eyes open. You may experience Braxton Hicks contractions — practice contractions that are irregular and painless.

Third Trimester (Weeks 28–40)

The home stretch. Baby is gaining about 200g per week, and your body is preparing for labor.

Weeks 28–32: Lung Maturation

Baby's lungs are maturing rapidly. Brain development accelerates. You may feel short of breath as the uterus pushes against your diaphragm. Prenatal visits increase to every 2 weeks.

Weeks 33–36: Getting into Position

Most babies turn head-down by week 36. You may feel "lightening" — baby drops lower into the pelvis, making breathing easier but increasing pelvic pressure. Group B Strep test is done around week 36.

Weeks 37–40: Full Term

Baby is considered early term at 37 weeks and full term at 39 weeks. The lungs and brain are still maturing until 39 weeks — this is why induction before 39 weeks is avoided unless medically necessary.

Baby Size Week by Week

Key Appointments & Tests

Tracking Your Pregnancy

Keeping track of symptoms, appointments, and baby's movements helps you stay informed and gives your doctor valuable data. Note when symptoms appear, track kick counts in the third trimester, and record questions for your next appointment.