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Pregnancy week by week
Your baby's development, size and weight, the changes in your body and practical tips for every week from week 1 to week 40. Reviewed general information that does not replace your doctor or midwife.
1st trimester · Weeks 1–13
- Week 1Dating from your last period
- Week 2The fertile window
- Week 3Fertilization and a traveling cluster of cells
- Week 4Implantation and the first positive tests
- Week 5Neural tube and a forming heart tube
- Week 6A heartbeat may flicker
- Week 7Limb buds lengthen
- Week 8Peak organ-building
- Week 9A more human outline
- Week 10Organs in miniature
- Week 11From embryo toward fetus
- Week 12Reflexes and a quieter miscarriage risk
- Week 13Stepping into the second trimester
2nd trimester · Weeks 14–27
- Week 14Swallowing and a growing thyroid
- Week 15Bones harden and legs catch up
- Week 16Hearing structures and meconium
- Week 17Brown fat and a stronger skeleton
- Week 18Nerves gain myelin and ears stand out
- Week 19Vernix and richer senses
- Week 20Halfway, and the anatomy scan window
- Week 21Bone marrow and more swallows
- Week 22Features sharpen; viability is still very limited
- Week 23Rapid brain growth and hearing voices
- Week 24Viability threshold and glucose screening
- Week 25Grasping hands and opening nostrils
- Week 26Eyes may open; third trimester is close
- Week 27REM sleep and practice breathing
3rd trimester · Weeks 28–40
- Week 28Third trimester and antibody timing
- Week 29Deeper brain grooves, softer skull
- Week 30Bone marrow takes over; lanugo thins
- Week 31All five senses in rehearsal
- Week 32Practice breathing and a possible head-down turn
- Week 33Antibodies crossing the placenta
- Week 34A more mature nervous system
- Week 35Kidneys mature; fat for warmth
- Week 36Early term is next; GBS swab week
- Week 37Early term — lungs are usually ready
- Week 38Full term is close
- Week 39Full term
- Week 40The due date is an estimate
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