Watch your unborn baby grow week by week - 1st Trimester of your pregnancy

From the early signs of pregnancy follow your baby's growing fetal development in this week by week guide with pictures through your 1st trimester

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  • Your pregnancy week by week

    Congratulations, you’re pregnant! Welcome to thinkbaby’s week by week guide to your growing baby’s development. Here you can discover all the amazing things that are happening inside your womb while you’re waiting for your baby to be born. Check out your baby's size each week at a glance. And have you signed up to our weekly email newsletter that tells you all about your baby's development?

  • The First Trimester of your pregnancy

    This is the first 12 weeks of pregnancy and a crucial period in terms of your baby’s development. By the end of the 12th week of pregnancy, all your baby’s major organs and body systems will be formed. During this time you might have worries over things like pregnancy bleeding, want to know when it's safe to announce the news of your baby and calculating your due date. But mostly you're going to want to know all about what's going to happen in the next 40 weeks of pregnancy, particularly how your baby is going to look. See your baby at two weeks

    *Remember, all pregnancies are different and foetal growth rates vary, this is meant only as an approximate guide to development. If you have any concerns about your developing pregnancy then speak to your doctor.

  • Pictures of your baby inside your tummy two weeks

    The 40 weeks of pregnancy start from the last day of your period. This means ‘week 2’ is around the point at which you conceive, because you’re most fertile in the middle of your cycle, two weeks after your last period. Find out more about your early pregnancy.

    Your egg and his sperm each have 23 chromosomes and together they form the 46 chromosomes which make up a human cell, the zygote. It splits into two cells, each with 46 chromosomes, then these divide again and again as they pass down the fallopian tube. By the time they reach the uterus there are about 100 cells – the building blocks for your baby. See your baby at three weeks

  • Pictures of your unborn baby at three weeks of your pregnancy

    This is a crucial week in your baby’s development. The mass of cells which has been steadily dividing since fertilisation is called the ‘blastocyst’ and is now ready to burrow its way into your womb lining (endometrium). This is called ‘implantation’ and can be one of the most tricky points in early pregnancy. Implantation can lead to something called Implantation bleeding which can be a cause for concern. Once the blastocyst has implanted then the embryo can receive the oxygen and nutrients from you to be able to grow. See your baby at four weeks

  • What's happening inside your pregnancy tummy at four weeks

    Now your baby-to-be is called an embryo, and is around the size of a pin head. The cells are dividing and multiplying rapidly, and three layers of cells have now formed – the outer layer (the ectoderm), which will develop into your baby’s brain, nervous system, skin, hair, nails and teeth; the middle layer (the mesoderm), which will become her heart and blood vessels, bones, muscles and reproductive organs; and the inner layer (the endoderm), which will develop into her lungs, liver, bladder and digestive system. The cells of the embryo grow lengthwise, assuming a leaner shape. See your baby at five weeks

  • Your unborn baby at five weeks of your pregnancy

    It’s a really exciting week - your baby is now the size of a poppy seed and by the end of the week her heart will be beating and the umbilical cord will have started to work - just one of the ways your body is helping to protect your baby. Your baby has a head end and a tail end and all the building blocks for her vital organs are in place. She is taking oxygen via the developing placenta, and the amniotic sac is also developing, which contains the fluid in which your baby will be protected and continue to grow. Check on your baby at six weeks

  • Pictures of your baby inside your tummy at six weeks

    Tiny limb buds for your baby’s arms and legs will appear and the starting blocks for facial features begin to take shape. His heartbeat can be picked up by an ultrasound scan. Other major organs like the kidneys, eyes and ears are beginning to form. He is also developing the tissue that will form his spine.

    By the end of this week your baby will be about half a centimetre long – no bigger than a grain of risotto rice – and shaped like a tadpole with a protrusion like a tail at the end of the spine. What's happening inside your tummy at 7 weeks

    Image from Your Pregnancy Day-by-Day by Professor Stuart Campbell (Carroll & Brown). Head to Carroll and Brown for more info on the book and other great pregnancy and parenting titles. www.carrollandbrown.co.uk

  • Pictures of your unborn baby at seven weeks pregnant

    This week your baby will more than double in size, from about 0.5cm to 1cm, and will make her first movements, twitching her developing limbs (you won’t be able to feel your baby’s movements for quite some time to come, probably between weeks 16 and 20). Her heart is becoming a four-chambered organ and beating about 150 beats a minute – twice as fast as yours.

    Her head and body are becoming more distinct, and the darkened specks of the eyes are forming along with the lungs, jaw and palate, the openings for the mouth, nose and ears, and the beginnings of tiny fingers and toes. See pictures of your baby inside the womb at 8 weeks

    Image from Your Pregnancy Day-by-Day by Professor Stuart Campbell (Carroll & Brown). Head to Carroll and Brown for more info on the book and other great pregnancy and parenting titles. www.carrollandbrown.co.uk

  • Pictures of your unborn baby at eight weeks of pregnancy

    Even though he’s around the size of a baked bean, about 1.5-2cm long, your baby now has the beginnings of every essential organ. He’s been stretching, bending and unbending and the development of the head is followed by the development of the abdomen and chest and the gradual disappearance of the tadpole-like tail. His tiny bones begin to form and your baby starts to look more like a miniature human being. The eyelids and tongue are now forming, as are follicles for the hair and nipples. Your baby can now demonstrate his first sensitivities to touch. Check out pictures of your unborn baby at 9 weeks

    Image from Your Pregnancy Day-by-Day by Professor Stuart Campbell (Carroll & Brown). Head to Carroll and Brown for more info on the book and other great pregnancy and parenting titles. www.carrollandbrown.co.uk

  • Pictures of your baby inside your tummy at nine weeks of your pregnancy

    She’s still so tiny, but your baby has grown to about 2-3cm long  - the size of a grape. Her limbs are well-formed and over this week her hands and feet begin to look more human – her hands will be able to bend at the wrist and your baby now has tiny little elbows! By the end of this week the eyelids are almost covering the eyes, and the sex organs are forming. Cute pictures of your baby at 10 weeks

    Image from Your Pregnancy Day-by-Day by Professor Stuart Campbell (Carroll & Brown). Head to Carroll and Brown for more info on the book and other great pregnancy and parenting titles. www.carrollandbrown.co.uk

  • Pictures of your unborn baby at 10 weeks of pregnancy

    Your baby is now officially a foetus. He’s about 2.5cm long, roughly the size of a strawberry, and the tail has gone. His arms have grown longer and the tiny fingers and toes have lost their webbing. His eyelids are beginning to fuse and, once shut, will stay that way until around the 26th week. The structure of the brain is complete and the external part of the ears are now completely formed, as is the top lip and he now has a large forehead and small nose. The skeleton is almost complete and between now and birth many of the bones will harden. Next week, your baby's the size of a tomato

    Image from Your Pregnancy Day-by-Day by Professor Stuart Campbell (Carroll & Brown). Head to Carroll and Brown for more info on the book and other great pregnancy and parenting titles. www.carrollandbrown.co.uk

  • See pictures of your unborn baby at 11 weeks of your pregnancy

    It’s a very busy week for your baby. She’s now around 5-6cm long and weighs about 8g– the size of a tomato. Her irises are beginning to develop and the ridges on her fingers are developing into tiny nails. The internal parts of the ears are now fully formed and the vital organs (brain, liver, kidneys, lungs and intestines) are fully functional. Her stomach is now moving into her abdominal cavity and the oesophagus, connecting the stomach and throat, will soon be complete. This will enable your baby to start swallowing amniotic fluid shortly. See your baby next week, it's the size of a lemon!

    Image from Your Pregnancy Day-by-Day by Professor Stuart Campbell (Carroll & Brown). Head to Carroll and Brown for more info on the book and other great pregnancy and parenting titles. www.carrollandbrown.co.uk

  • Pictures of your unborn baby at 12 weeks of your pregnancy

    Congratulations, you’re now at the end of your first trimester! Your baby now spans between 5 and 7 centimetres (around the size of a small lemon) and weighs around 14g, or half an ounce. He has all his essential parts and for the next six months will devote most of his energy to growing and developing ready for life outside your womb. With the rest of his energy he’ll be busy moving around, kicking, boxing (!) and punching while floating in the amniotic fluid (you won’t be able to feel this until 16-20 weeks).

    Image from Your Pregnancy Day-by-Day by Professor Stuart Campbell (Carroll & Brown). Head to Carroll and Brown for more info on the book and other great pregnancy and parenting titles. www.carrollandbrown.co.uk

    See how your baby's going to develop in your second trimester

    What's going to happen in your third trimester

Last updated on 6 June 2011

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