Pregnancy Trimesters Explained
Pregnancy is divided into three trimesters spanning 40 weeks. Here is a complete breakdown of what happens during each stage — for both you and your baby.
Medically reviewed by
MBBS, MD — Gynecologist & Obstetrician
Last reviewed:
Feb 2026
🌱
First Trimester
Weeks 1–13
The most critical period for fetal development. Major organs form, and the risk of miscarriage is highest during this trimester.
🍼 Baby's Development
- Fertilization and implantation (week 3)
- Heart begins beating (~week 6)
- Brain, spinal cord, and organs begin forming
- Arms, legs, fingers, and toes develop
- Baby transitions from embryo to fetus at week 9
- All major organs present by week 12
- Crown-rump length: 0 → ~6.5 cm by week 12
🤰 Your Symptoms
- Missed period and positive pregnancy test
- Nausea and vomiting (morning sickness)
- Extreme fatigue
- Breast tenderness and enlargement
- Frequent urination
- Food aversions and cravings
- Mood swings
🏥 Medical Tests
- Confirmation of pregnancy (hCG blood test)
- First prenatal visit (8–10 weeks)
- Nuchal translucency ultrasound (11–14 weeks)
- First-trimester blood screening (chromosomal markers)
- Cell-free fetal DNA (NIPT) — optional
- Blood type, CBC, rubella immunity, STI screening
🌟
Second Trimester
Weeks 14–27
Often called the 'golden trimester' — nausea typically eases, energy returns, and you begin to feel your baby move.
🍼 Baby's Development
- Baby's movements first felt (quickening) at 16–22 weeks
- Lanugo (fine hair) covers the body
- Vernix caseosa (protective coating) forms
- Eyes and ears reach final position
- Fingerprints develop
- Lungs begin practicing breathing movements
- Weight: ~500g by week 24, ~1kg by week 27
🤰 Your Symptoms
- Energy levels improve
- Baby bump becomes visible
- Round ligament pain
- Back pain begins
- Nasal congestion and nosebleeds
- Skin changes (linea nigra, melasma)
- Leg cramps
- Braxton Hicks contractions (practice contractions)
🏥 Medical Tests
- Anatomy scan (18–22 weeks) — detailed fetal survey
- Quad screen blood test (15–20 weeks)
- Amniocentesis if indicated (16–20 weeks)
- Glucose challenge test (24–28 weeks)
- CBC and iron levels
🏁
Third Trimester
Weeks 28–40+
Final preparation for birth. Baby gains most of its weight, and your body prepares for labor and delivery.
🍼 Baby's Development
- Rapid weight gain (gains ~200–250g per week)
- Brain develops rapidly
- Lungs continue maturing
- Baby moves into head-down position (by ~36 weeks)
- Eyes open and close; responds to light and sound
- Immune system develops
- Full term: 39–40 weeks (typically 3–4 kg)
🤰 Your Symptoms
- Shortness of breath as uterus expands
- Heartburn and indigestion
- Frequent urination returns
- Swollen ankles and feet (edema)
- Difficulty sleeping
- Pelvic pressure and discomfort
- Nesting instinct
- Colostrum leaking from breasts
🏥 Medical Tests
- Kick count monitoring (from 28 weeks)
- GBS (Group B Streptococcus) test (35–37 weeks)
- Cervical checks in late pregnancy
- Biophysical profile or NST if post-dates
- Growth scan if concerns about size
Frequently Asked Questions
Common questions answered by our medical team
The first trimester spans weeks 1–13 (about 13 weeks). The second trimester spans weeks 14–27 (about 14 weeks). The third trimester spans weeks 28–40+ (about 13 weeks). Total pregnancy duration is approximately 40 weeks.