Pregnancy Week by Week: Baby Development, Symptoms & Milestones

Pregnancy lasts approximately 40 weeks from the first day of your last menstrual period (LMP), divided into three trimesters. Each week brings measurable changes in your baby's development and your own body — knowing what to expect makes the journey far less uncertain.

Weeks 1–4: The first month begins before you even know you are pregnant. Week 1 is your period itself; fertilization typically occurs in week 2 or 3 depending on your cycle length. By week 4, the fertilized egg implants in your uterine lining and begins releasing hCG — the hormone that makes a pregnancy test positive. You may notice light spotting (implantation bleeding), mild cramping, or no symptoms at all.

Weeks 5–8: Your baby's heart begins beating around week 6, detectable by transvaginal ultrasound. The embryo is now growing arm and leg buds, and the neural tube — which becomes the brain and spinal cord — is forming. This is when most women experience the first wave of nausea, fatigue, and breast tenderness. Your first prenatal appointment typically happens in this window.

Weeks 9–12: By the end of the first trimester, your baby is officially called a fetus. Fingers, toes, and all major organs are present in early form. The risk of miscarriage drops sharply after week 10. Your first trimester screening (nuchal translucency ultrasound + blood tests) is typically scheduled between weeks 11 and 13.

Weeks 13–16: Welcome to the second trimester — most women find this the most comfortable stretch. Energy returns and nausea often fades. Your baby can now make facial expressions and begins swallowing amniotic fluid. The anatomy scan (detailed ultrasound) is typically scheduled between weeks 18 and 22. Many parents learn the sex of their baby during this scan.

Weeks 17–24: This is when you will likely feel your baby's first movements — a sensation called quickening, which feels like flutters or bubbles. Your baby develops hearing around week 18 and can respond to sound by week 25. The anatomy scan checks for structural abnormalities and confirms placenta position. By week 24, your baby has reached the threshold of viability outside the womb.

Weeks 25–32: The third trimester begins at week 28. Your baby is rapidly gaining weight and fat stores. Brain development accelerates. You may feel Braxton Hicks contractions — practice contractions that tighten and release without causing labor. Your prenatal visits become more frequent (every 2–3 weeks), and your provider will begin checking fetal position. Group B Streptococcus (GBS) testing happens around week 36.

Weeks 33–40: Your baby is considered full-term at week 39. In these final weeks, the baby settles into the head-down position (most commonly), and your cervix begins to soften and thin (efface) in preparation for labor. Watch for signs of labor: regular contractions, water breaking, bloody show. Track kick counts daily — 10 movements within 2 hours is the standard benchmark. Use TrackWise-AI to log fetal movement, contractions, and symptoms so you have accurate data to share with your provider.

What to track throughout your pregnancy: prenatal appointments and their results, weight gain by week, blood pressure readings, baby movement counts, symptoms and their severity, lab results and ultrasound findings, medication and supplement records, and any questions for your doctor. Having this data organized means every appointment is more productive and nothing falls through the cracks.