Pregnancy Week by Week
A brief tour of the 40 weeks: how your baby grows from a poppy seed to a watermelon, the milestones that matter, and what most women notice along the way. Every pregnancy is different — use this as a map, not a timetable.
First trimester (weeks 1–13)
| Week | Baby's size | Your baby | You |
|---|---|---|---|
| Week 4 | About a poppy seed ≈ 2 mm | The embryo implants in the womb; the neural tube — which becomes the brain and spine — begins to form. | Your period is missed around now. A home pregnancy test usually turns positive. |
| Week 6 | About a lentil ≈ 6 mm | The heart begins to beat and can often be seen flickering on an early ultrasound. | Nausea, tiredness and sore breasts commonly begin as hormone levels climb. |
| Week 8 | About a raspberry ≈ 1.6 cm | All essential organs have begun to form; tiny arms and legs are budding. | Your first booking appointment with a midwife or doctor usually happens around now. |
| Week 10 | About a strawberry ≈ 3.1 cm | Elbows can bend, tooth buds form, and the baby starts small, spontaneous movements. | Screening tests for chromosomal conditions are offered from around this point. |
| Week 12 | About a lime ≈ 5.4 cm | Fingers and toes have separated; reflexes begin. The first trimester is nearly complete. | The dating scan is usually done between 11 and 14 weeks — many parents see their baby for the first time. |
Second trimester (weeks 14–27)
| Week | Baby's size | Your baby | You |
|---|---|---|---|
| Week 16 | About an avocado ≈ 11.6 cm | The baby can make facial expressions and may start sucking its thumb; the ears are nearly in place. | Many women feel a lift in energy — and the earliest fluttering movements, especially in later pregnancies. |
| Week 20 | About a banana ≈ 25.7 cm (head to heel) | Halfway there. The anatomy scan checks the baby's organs, limbs and growth in detail. | First unmistakable kicks often arrive around now. Your bump becomes clearly visible. |
| Week 24 | About a cantaloupe melon ≈ 30 cm | The lungs are developing air sacs; from 24 weeks a baby has a chance of survival if born, with specialist care. | Glucose screening for gestational diabetes is typically offered between 24 and 28 weeks. |
| Week 26 | About a head of lettuce ≈ 35.6 cm | The eyes begin to open and the baby responds to sounds from outside the womb. | Backache and heartburn may appear as your centre of gravity shifts. |
Third trimester (weeks 28–40)
| Week | Baby's size | Your baby | You |
|---|---|---|---|
| Week 28 | About an aubergine (eggplant) ≈ 37.6 cm | The baby can blink, dream sleep begins, and weight gain speeds up from here. | The third trimester starts. Appointments become more frequent; blood pressure is checked at each one. |
| Week 32 | About a coconut ≈ 42.4 cm | Most babies settle into a head-down position around this stage, readying for birth. | Braxton Hicks practice contractions are common. Sleep can get harder — pillows help. |
| Week 36 | About a romaine lettuce head ≈ 47.4 cm | The baby is putting on about 200 g (7 oz) a week now, mostly as fat stores for birth. | Your provider checks the baby's position; you may discuss your birth preferences and plan. |
| Week 40 | About a small watermelon ≈ 51.7 cm | Full term. The average newborn weighs about 3.4 kg (7 lb 8 oz) — though healthy babies vary widely. | Your due date arrives — but only about 1 in 20 babies do. Most come within the following two weeks. |
Don't know your dates yet? Work out where you are with the due date calculator — it shows your current week, your trimester, and the dates of the milestones above for your own pregnancy.
This calculator is for general information only and is not medical advice. Pregnancy dating can vary — always confirm your due date and any health decisions with your doctor, midwife or healthcare provider.