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Your Growing Baby During Pregnancy


Your baby's journey from conception to birth. Discover how your baby grows during your 40 weeks of pregnancy.


Week 4

Length 3 mm

My heart has started to beat! My facial features have begun to appear and my arms and legs have started to grow.

Week 7

Length 5mm

I’ve grown to look like a small bean, with a head that is much larger than my body. My tail is disappearing, my arms and legs protrude more and my hands and feet are paddle-shaped. There are dark spots on the sides of my head, which are my eyes forming. Little openings on my face mark my nostrils, and my ears are developing. My heart is going 150 beats a minute—that's a lot faster than my mum's.

Week 12

Length 6cm
Weight 11g

I’ve acquired all the individual features that make me ME. I’ve doubled in size over the past three weeks. My fingers and toes have separated, my hair is growing and my bones are strengthening as my body lays down calcium. I jump about and stretch my arms and legs. My genital organs are discernible (an expert can tell if I’m a boy or a girl). My digestive system can absorb glucose or sugar and it contracts to push food through my bowels.

baby 12cm 250Week 17

Length 11cm
Weight 100g

I can bend my fingers into fists and make different facial expressions: I can frown and grimace. There’s fine hair, or lanugo, on my body to help regulate my temperature. My head is starting to look in proportion to my body. My eyes are closed but larger, and I have eyelashes as well as fingernails and toenails. I like to put my hand in my mouth. My chest rises and falls to practice breathing and fluid passed through my air passages.

Week 18

Length 13cm
Weight 150g

My respiratory system is among the last things to mature but tiny air sacs are developing in my lungs. I have fingertip pads, and the swirls that will be fingerprints begin to appear. I enjoy punching, kicking and wriggling. My eyes are in their correct position, although the lids mostly stay closed until week 24. Undigested debris from swallowed amniotic fluid is collecting in my lower bowel. If I’m a boy, my prostate will be forming.

Week 23

Length 20cm
Weight 455g

My skin is less transparent as I begin to look more like a full-term baby. I don’t have much fat, so it is wrinkly. I have distinct lips and tooth buds under my gum. My hearing is more acute now because the bones of my inner ear have hardened. I can hear dad’s deeper voice more easily than mum’s higher pitched one. My eyes are formed but the irises lack colour pigment. My pancreas is developing.

Week 25

Length 22cm
Weight 700g

I am more in proportion now. Blood vessels continue to develop in my lungs and my nostrils open. High in my gums, my permanent teeth begin, but these won’t descend until my milk teeth fall out when I’m about six years old. The nerves around my mouth are more sensitive and I like to suck my thumb. My lungs are the only vital organs to still fully develop. If I’m a girl, my genitals are formed into a hollow tube. My umbilical cord is thick.

pregnant smiling water flipped 250

Week 27

Length 24cm
Weight 1kg

My eyes are now complete—the final layers of my retina in the back of them have formed. My eyelids can open some of the time and my eyelashes are fully grown and are helping to protect my eyes from harmful matter. I am becoming more rounded and plump because of increased fat being deposited under my skin. My lungs continue to grow and I have fully functioning taste buds on my tongue and inside my cheeks.

Week 29

Length 26cm
Weight 1.25kg

I’m beginning to assert myself. I’ve got just enough room to stretch my arms and legs but I can still get in the odd kick. My mum will normally feel up to 10 kicks in one morning. Here I am yawning, which I’ve been able to do since about 11 weeks. My brain is getting pretty powerful: it controls my breathing and body temperature. My eye lenses move during sleep – they are more sensitive to light and dark, but I won’t use this ability until birth. 

Week 30

Length 27cm
Weight 1.36kg

The hair that covered my body is disappearing. A few patches may be left at birth but will rub off after a few weeks. My skin looks less wrinkled because I’ve put on more baby fat. My bone marrow has taken over red blood cell production from my liver. My skeleton is hardening and my brain, muscles and lungs continue to mature. If I hear a noise, I will react to it with a kick. I increasingly open and close my eyes and I can breathe rhythmically.

Week 33

Length 30cm
Weight 2kg

Because of my rapid growth, my head is 9.5cm in circumference—in correct proportion to my body. My bones are fully developed, though soft and pliable. I’m starting to store iron, calcium and phosphorous, vital for bone development. My skin becomes pinker as I accumulate more fat. I am more aware of my surroundings, including external noises and the things in my immediate environment, such as amniotic fluid.

unborn baby third trimester 250Week 35

Length 33cm
Weight 2.55kg

I’m getting plumper now, as I acquire more body fat, which will later help to regulate my body temperature. There’s hardly any room to move and I’m getting squashed. My central nervous system is maturing and I’m increasingly awake and aware. My digestive system is almost complete and my lungs are nearly fully mature. Like mine in this picture, some babies’ heads will now be engaged in the birth canal.

Week 38

Length 38cm
Weight 3.25kg

I can be born at any time. My abdominal circumference is now slightly larger than my head and I have 15 per cent body fat. All my body systems have developed. I have at least 70 reflexes to help me cope with life outside the uterus. The placenta, which has sustained me all these weeks, is becoming less efficient. There is less amniotic fluid. My first breaths of air will trigger my heart and arteries to transfer blood to my lungs.

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