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YOUR UNBORN BABY WEEK BY WEEK

Pregnancy lasts for approximately 40 weeks and is dated from the first day of your last period. If your last period was 8 weeks ago you will be considered 8 weeks’ pregnant even though your baby is only probably 6 weeks old.

  • Week 4 of pregnancy – Your baby is 2 weeks old and measures 0.36-1mm from crown to rump.
  • Week 5 of pregnancy – Your baby is 3 weeks old and measures about 1.25cm from crown to rump. A head and tail are now visible, the central nervous system begins to develop and your baby’s brain and spinal cord start to form. Traces of eyes and ears can be seen and his liver, kidneys, muscle and bone are starting to develop.
  • Week 6 of pregnancy – Your baby is now 4 weeks old and measures 2-4 mm from crown to rump. Your baby now has a brain and his heart is beating independently. His other major organs continue to develop, the neural tube connecting his brain and spinal cord closes, and his head begins to take shape. A basic digestive tract, abdominal and chest cavities, the backbone and limb buds start to form.
  • Week 7 of pregnancy – Your baby is now 5 weeks old and measures 4-5mm from crown to rump. The dark spots on the sides of her head will become her eyes, and she has the beginnings of nostrils, lips, a tongue and her first tooth buds. Her limbs have lengthened and she has basic hands and feet. Her heart, liver, kidneys, lungs, intestines and internal sex organs are nearly complete.
  • Week 8 of pregnancy – Your baby is now 6 weeks old and measures about 14-20mm from crown to rump. Her jaw is fusing to shape her mouth, her intestines are starting to develop in the umbilical cord, bone cells are forming to replace cartilage, and her leg and arm bones are hardening and lengthening.
  • Week 9 of pregnancy – Your baby is 7 weeks old and measures 22-30mm from crown to rump. His hands, feet and limbs are growing very quickly and his fingers and toes are nearly fully formed. His eyelids almost cover his eyes and his nose is formed. The diaphragm starts to develop and his intestines begin to move out of the umbilical cord and into the abdomen.
  • Week 10 of pregnancy – Your baby is 8 weeks old, measures roughly 31-42 mm from crown to rump, and weighs about 5g. Most of his joints have formed and genitals are also developing, although it is still not possible to determine the sex. The nervous system is responsive and many of the internal organs are starting to function.
  • Week 11 of pregnancy – Your baby is 9 weeks old and measures 44-60mm from crown to rump, weighing about 8g. The critical stage of development has passed and from now it’s all about growth. By the end of this week her body will have doubled in length and her head will be almost half the length of her body. The vital organs – liver, kidneys, intestines, brain and lungs – are completely developed now and starting to work. Your baby can already yawn, suck and swallow. Fingernails and hair start to appear.
  • Week 12 of pregnancy – Your baby is 10 weeks old, measures about 61mm from crown to rump and weighs between 8 and 14g. She is fully formed but her organs and especially her brain are still developing. She can now smile, frown and suck her thumb and also move her arms, fingers and toes.
  • Week 13 of pregnancy – Your baby is now 11 weeks old, measures 65-78mm and weighs 13- 20g. Although fully formed, he still cannot survive outside the uterus as his internal organs, especially his lungs, are not yet mature enough. He is able to sense sounds.

  • Week 14 of pregnancy – Your baby is now 12 weeks old, measures 80-93mm and weighs nearly 25g. This is the start of the second trimester. Your baby’s nervous system has begun to function and he practises breathing movements although all his oxygen comes from you via the umbilical cord and placenta.
  • Week 15 of pregnancy – Your baby now measures approximately 104-114mm from crown to rump and weighs around 50g. Extra fine hair called lanugo starts to cover her skin to help regulate her body temperature. The mechanisms allowing your baby to hear are forming and she will begin to hear your voice and heartbeat.
  • Week 16 of pregnancy – Your baby measures about 108-116mm from crown to rump and weighs 80g. Your baby is extremely active and can now co-ordinate her movements. You can now find out the sex of your baby on an ultrasound scan.
  • Week 17 of pregnancy: Your baby measures around 11-12cm from crown to rump and weighs about 100g. Fat starts to be laid down under his skin which helps keep him warm and give him energy. He can now hear sounds outside your body. His chest rises and falls as he practises breathing and his lungs are beginning to exhale amniotic fluid.
  • Week 18 of pregnancy – Your baby measures 12.5-14cm from crown to rump and weighs around 150g. She is starting her most active phase now. Her unique fingerprints have begun to appear, her eyes are now in the correct position, and meconium (which will form her first poo) is building up in her bowels.
  • Week 19 of pregnancy – Your baby measures about 13-15cm from crown to rump and weighs approximately 200g. Glands in his skin secrete vernix caseosa, a waterproof barrier that protects his skin. Your baby’s gut has started to produce gastric juices.
  • Week 20 of pregnancy – Your baby measures 14-16cm from crown to rump and weighs about 255g. This is an important stage for the development of your baby’s senses (taste, smell, hearing, sight and touch) and the complex neural connections needed for the development of memory and thinking. Your baby can now recognise your voice. If your baby is a girl she has about 2 million eggs in her ovaries already.
  • Week 21 of pregnancy – Your baby now measures about 16cm from crown to rump and weighs around 300g. His digestive system is developed enough to absorb water from the amniotic fluid he swallows. Taste buds have formed on his tongue and he can sense touch.
  • Week 22 of pregnancy – Your baby measures about 19cm from crown to rump and weighs about 350g. He has sweat glands and his brain is growing rapidly. If your baby is a boy, his testes have begun to descend from the pelvis to the scrotum and primitive sperm have already formed in the testes.
  • Week 23 of pregnancy – Your baby is starting to look like a full-term baby now but her skin is still transparent. The bones of her inner ear have hardened and her hearing is much sharper. Talk to her as much as possible.
  • Week 24 of pregnancy – Your baby measures about 21cm from crown to rump and weighs approximately 540g. Her lungs have developed enough to give her a chance at surviving in a neonatal ICU if she were born.
  • Week 25 of pregnancy – Your baby measures about 22cm from crown to rump and weighs around 700g. He can hold his feet and curl his hand into a fist. His nostrils begin to open and his permanent teeth are beginning to develop. Nerves around his mouth are also developing in preparation for finding the nipple.
  • Week 26 of pregnancy – Your baby’s spine is getting stronger and suppler and Dad may be able to hear her heartbeat by putting his ear to your tummy. Baby’s pulse quickens when she reacts to sounds and she may even move in time to music!
  • Week 27 of pregnancy – Your baby measures about 24cm from crown to rump and weighs just over 1kg. He is becoming plumper, he has fully functioning taste buds and his eyelids are beginning to open.

  • Week 28 of pregnancy – Your baby is about 25cm in length from crown to rump and weighs about 1.1kg. Her lungs are capable of breathing air but she would still find it very hard to breathe on her own is she were born now. She loves your voice so keep talking to her. After 28 weeks, you should be able to count at least 10 movements every twelve hours after you are twenty-eight weeks pregnant. Call your doctor immediately if you get less than this or you notice a significant decrease in your baby’s movement.
  • Week 29 of pregnancy – Your baby measures around 26cm from crown to rump and weighs about 1.25kg. His brain is growing quickly and can now control his breathing and body temperature. His eyes can move in their sockets.
  • Week 30 of pregnancy – Your baby is approximately 27cm in length from crown to rump and about 1.36kg in weight. A lot of babies will move into the head-down position which is the most common position for birth. Expect to feel strong kicks under your ribcage and pressure on your pelvic floor!
  • Week 31 of pregnancy – Your baby is about 28cm from crown to rump and weighs about 1.59kg. His growth starts to slow down but his weight gain continues. His lungs are the last major organs to mature. His eye colour starts to show now but his true colour won’t show for six to nine months after his birth.
  • Week 32 of pregnancy – Your baby’s length from crown to rump is about 29cm and weight is around 1.8kg. All five senses are working, organs are continuing to mature, toenails are complete and hair is still growing. Baby sleeps more than 90 percent of the day.
  • Week 33 of pregnancy – Your baby is almost 30cm from crown to rump and will weigh about 2kg. Her head has enlarged due to the rapidly growing brain and fat accumulation turns her skin from red to pink.
  • Week 34 of pregnancy – Your baby measures 32cm from crown to rump and weighs as much as 2.28kg. Her immune system is developing so as to fight mild infection. Her movements are bigger and slower and she may be in the head-down position now. Around 3% of babies will be lying with their legs or bottoms towards the cervix in the breech position.
  • Week 35 of pregnancy – Your baby’s length is around 33cm from crown to rump and he weighs over 2.55kg. His central nervous system is maturing, the lungs are fully mature and the digestive system is almost finished.
  • Week 36 of pregnancy – Your baby is about 34cm in length from crown to rump and weighs about 2.75kg. You will notice that her movements are fewer but stronger and more precise. You might even be able to see the outline of certain body parts like an elbow appearing under your skin.
  • Week 37 of pregnancy – Your baby will be about 35cm from crown to rump and will weigh nearly 2.95kg. He is considered full-term and could be born any day now. If labour starts, there is no reason to delay it.
  • Week 38 of pregnancy – Your baby measures 35cm from crown to rump and weighs around 3.1kg. All body systems have developed and the circumference of her head and abdomen are about the same. Your doctor may be able to estimate her birth weight at this stage.
  • Week 39 of pregnancy – Your baby is about 36cm from crown to rump and weighs just over 3.25kg. Your body produces pregnancy hormones which may temporarily cause the breasts in male and female newborns to be swollen and the genitalia to appear enlarged. These side effects will disappear after birth.
  • Week 40 of pregnancy – Your baby measures 38cm from crown to rump and about 51cm from head to toe. Fifteen percent of her body is fat and she is ready to start life outside the uterus. At birth, the placenta peels away from the side of the uterus and the umbilical cord stops working as your baby takes her first breaths. Her breathing triggers changes in the structure of her heart and arteries, which diverts blood to her lungs.