Pregnancy Week by Week: Weeks 1–40 Guide | Pregnancy Week to Week
A sourced, informational week-by-week guide to pregnancy — typical baby development and common symptoms for every week from 1 to 40.
A sourced, week-by-week guide to pregnancy from week 1 to week 40 — what is typically happening with the baby and the common changes people may notice each week, grouped by trimester. Every week is informational only and cites reputable medical authorities. See our sourcing & review policy →
Week 1FirstWeek 2FirstWeek 3FirstWeek 4FirstWeek 5FirstWeek 6FirstWeek 7FirstWeek 8FirstWeek 9FirstWeek 10FirstWeek 11FirstWeek 12FirstWeek 13FirstWeek 14SecondWeek 15SecondWeek 16SecondWeek 17SecondWeek 18SecondWeek 19SecondWeek 20SecondWeek 21SecondWeek 22SecondWeek 23SecondWeek 24SecondWeek 25SecondWeek 26SecondWeek 27SecondWeek 28ThirdWeek 29ThirdWeek 30ThirdWeek 31ThirdWeek 32ThirdWeek 33ThirdWeek 34ThirdWeek 35ThirdWeek 36ThirdWeek 37ThirdWeek 38ThirdWeek 39ThirdWeek 40Third
The full week-by-week table
| Week | Trimester | Approx. size | Typical development |
|---|---|---|---|
| Week 1 | First | — | In weeks 1–2 conception has not yet occurred; hormone levels build a thick uterine lining and the body prepares to ovulate. |
| Week 2 | First | — | Development in the first two weeks is general; ovulation and fertilisation occur around the end of this period. |
| Week 3 | First | about 0.006 inch (0.15 mm) — roughly the size of the head of a pin | The fertilised egg multiplies into a ball of cells called a blastocyst and begins to implant in the uterine lining. |
| Week 4 | First | about the size of a poppy seed | The embryo implants fully; the placenta and amniotic sac begin to form and the embryonic period starts. |
| Week 5 | First | about the size of a sesame seed | The neural tube (future brain and spinal cord) forms; the heart begins to develop and beat. |
| Week 6 | First | about the size of a lentil | Facial features, limb buds, and the heartbeat take shape; the heart beats around 100–160 times a minute. |
| Week 7 | First | about the size of a blueberry | The brain grows quickly; hands and feet begin as paddle-like buds; major organs continue forming. |
| Week 8 | First | about the size of a raspberry | Fingers and toes begin to form and webbing recedes; the embryo makes small movements. |
| Week 9 | First | about the size of a grape | The embryo becomes a fetus; essential organs are present and the heart has four chambers. |
| Week 10 | First | about the size of a kumquat | Vital organs are formed and beginning to function; tiny nails start to develop. |
| Week 11 | First | about the size of a fig | The head is large relative to the body; bones begin to harden and the baby can move freely. |
| Week 12 | First | about the size of a lime | Reflexes develop; the baby can open and close its hands; the digestive system practises contractions. |
| Week 13 | First | about the size of a pea pod | Vocal cords form; fingerprints appear; the baby's body begins to catch up to the head in size. |
| Week 14 | Second | about the size of a lemon | The baby can make facial expressions; fine hair (lanugo) starts to grow; the kidneys produce urine. |
| Week 15 | Second | about the size of an apple | The baby can sense light; bones continue to harden; it moves, though movement is usually not yet felt. |
| Week 16 | Second | about the size of an avocado | The baby's eyes can move and it may make sucking motions; the heart pumps a substantial amount of blood daily. |
| Week 17 | Second | about the size of a pear | Body fat begins to form; the skeleton shifts from soft cartilage to bone; the umbilical cord strengthens. |
| Week 18 | Second | about the size of a bell pepper | Hearing develops and the baby may respond to sounds; the digestive system is active. |
| Week 19 | Second | about the size of a mango | A protective waxy coating (vernix caseosa) forms on the skin; sensory areas of the brain develop. |
| Week 20 | Second | about the size of a banana | The halfway point; the baby is active, swallows, and has a sleep–wake pattern. |
| Week 21 | Second | about the size of a carrot | The baby gains weight steadily; taste buds form and it can taste the amniotic fluid. |
| Week 22 | Second | about the size of a spaghetti squash | Fine hair and eyebrows are visible; the lips and eyes are more developed. |
| Week 23 | Second | about the size of a large mango | The lungs develop blood vessels in preparation for breathing; the baby responds to sound and movement. |
| Week 24 | Second | about the size of an ear of corn | A point of viability is often described around now; the lungs and brain continue maturing. |
| Week 25 | Second | about the size of a rutabaga | The baby responds to familiar voices; fat continues to build and skin becomes less translucent. |
| Week 26 | Second | about the size of a head of lettuce | The eyes begin to open; the lungs make surfactant; brain activity increases. |
| Week 27 | Second | about the size of a cauliflower | The baby has regular sleep cycles, may hiccup, and the brain develops rapidly. |
| Week 28 | Third | about the size of an eggplant | Eyes can open and close; the baby may turn toward light; rapid brain and lung development continues. |
| Week 29 | Third | about the size of a butternut squash | Muscles and lungs mature; the baby's head grows to accommodate the developing brain. |
| Week 30 | Third | about the size of a large cabbage | The baby can distinguish light from dark; bone marrow takes over red-blood-cell production. |
| Week 31 | Third | about the size of a coconut | The baby gains weight quickly; all five senses are working; it may practise breathing movements. |
| Week 32 | Third | about the size of a squash | The baby often settles into a head-down position; fingernails reach the fingertips. |
| Week 33 | Third | about the size of a pineapple | The bones harden (except the soft skull plates); the immune system strengthens. |
| Week 34 | Third | about the size of a cantaloupe | The lungs are nearly mature; the baby practises breathing and the central nervous system develops. |
| Week 35 | Third | about the size of a honeydew melon | Most development is complete; the baby is mainly gaining weight now. |
| Week 36 | Third | about the size of romaine lettuce | The baby is usually head-down; lungs and digestive system are nearly ready for birth. |
| Week 37 | Third | about the size of a bunch of Swiss chard | At 37 weeks the pregnancy is 'early term'; the baby continues to mature and gain weight. |
| Week 38 | Third | about the size of a leek | The baby's organs are ready to function; it builds fat for temperature control after birth. |
| Week 39 | Third | about the size of a small watermelon | At 39 weeks the pregnancy is 'full term'; the baby is ready for birth. |
| Week 40 | Third | about the size of a pumpkin | The due date arrives; the baby is fully developed, though many babies arrive a little before or after. |
Informational only — not medical advice. Pregnancy Week to Week is a general educational reference. It is not a substitute for professional medical care, diagnosis, or treatment. Every pregnancy is different: always consult your doctor, midwife, or other qualified healthcare provider about your own pregnancy, and never disregard or delay professional advice because of something you read here. In an emergency, contact your maternity unit or local emergency number immediately.
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