Pregnancy week by week, weeks 1 to 40
What your baby is doing, how your body may feel, and the self-care that matters most — written in plain language and aligned with WHO antenatal care recommendations and NICE guidance. Educational only; it never replaces advice from your own midwife or doctor.
First trimester · Weeks 1–13
Size: not yet conceived — this week is counted from your last period
Pregnancy is dated from the first day of your last period, so conception has not happened yet. Your body is shedding the uterine lining and preparing a fresh one.
Week 2Size: a single egg, smaller than a grain of sand
An egg is maturing and your body is preparing to release it. Fertilisation usually happens at the end of this week.
Week 3Size: a cluster of cells, about the size of a pinhead
The fertilised egg divides as it travels down the fallopian tube towards the uterus.
Week 4Size: a poppy seed
The embryo settles into the uterine lining and the placenta starts to form.
Week 5Size: a sesame seed
The neural tube — which becomes the brain and spine — is forming, and a tiny heart begins to beat.
Week 6Size: a lentil
Facial features, arm and leg buds begin to appear. The heartbeat can often be seen on an early scan.
Week 7Size: a blueberry
The brain is growing quickly and tiny hands and feet are starting to form.
Week 8Size: a raspberry
The baby is now moving, though far too small for you to feel it. Fingers and toes are separating.
Week 9Size: a grape
The heart has four chambers and essential organs continue developing.
Week 10Size: a strawberry
The baby is now called a fetus. Vital organs are formed and will grow from here.
Week 11Size: a fig
Bones are hardening and the baby can hiccup, though you cannot feel it yet.
Week 12Size: a lime
Reflexes are developing, fingers and toes are fully separated and the face looks more human.
Week 13Size: a pea pod
Vocal cords form and the baby starts producing urine into the amniotic fluid.
Second trimester · Weeks 14–27
Size: a lemon
The baby can squint, frown and suck a thumb. Fine hair called lanugo begins to grow.
Week 15Size: an apple
The baby can sense light through the closed eyelids and is moving freely.
Week 16Size: an avocado
Facial muscles work, the baby can hear muffled sounds, and growth is rapid.
Week 17Size: a pear
Fat begins to form under the skin and the skeleton hardens from cartilage to bone.
Week 18Size: a sweet potato
The baby yawns, stretches and hears your heartbeat and voice.
Week 19Size: a mango
A protective coating called vernix covers the skin, and the senses are developing quickly.
Week 20Size: a banana
Halfway there. The baby swallows amniotic fluid and produces first stool, called meconium.
Week 21Size: a carrot
Movements become stronger and a sleep–wake rhythm begins to form.
Week 22Size: a papaya
Eyebrows and lips are visible and the baby responds to sound and touch.
Week 23Size: a large mango
Lungs are developing surfactant, and hearing is sharp enough to recognise your voice.
Week 24Size: an ear of corn
The baby reaches an important stage of lung and brain development.
Week 25Size: a cauliflower
The baby's hands can grip and the sense of balance is developing.
Week 26Size: a lettuce
Eyes begin to open and the baby responds to bright light.
Week 27Size: a head of broccoli
Regular sleep cycles form and the baby may hiccup — small rhythmic jumps you can feel.
Third trimester · Weeks 28–40
Size: an aubergine
The baby's brain grows rapidly and eyes can blink.
Week 29Size: a butternut squash
Muscles and lungs continue maturing and the baby gains weight steadily.
Week 30Size: a large cabbage
The baby can distinguish light and dark and practises breathing movements.
Week 31Size: a coconut
All five senses are working and the baby responds to your movement and voice.
Week 32Size: a squash
Most babies move head-down around now, preparing for birth.
Week 33Size: a pineapple
The immune system strengthens as antibodies pass from you to the baby.
Week 34Size: a melon
Fingernails reach the fingertips and fat continues building under the skin.
Week 35Size: a honeydew melon
Lungs are nearly mature and the baby practises breathing rhythmically.
Week 36Size: a romaine lettuce head
The baby is gaining around 30 grams a day and settling into a birth position.
Week 37Size: a swiss chard bunch
The baby is early term. Organs are ready, although the brain keeps developing.
Week 38Size: a leek
The baby continues gaining fat and shedding the fine body hair.
Week 39Size: a small watermelon
The baby is full term with fully developed lungs, ready to breathe air.
Week 40Size: a pumpkin
Your baby is fully grown and ready to be born. Many babies arrive in the week or two after 40 weeks.