Your pregnancy: weeks 38, 39, 40

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This guide to your pregnancy tells you how your baby is developing week by week. It also tells you a bit about how your body may be changing and how you might be feeling. Remember, not all babies develop exactly like each other so this can only be a general guide: you should ask your doctor or midwife for any specific information about your pregnancy. We all know babies come in two flavours, but - as most of you won't know what flavour you're getting - for clarity we will refer to your baby as "she".

How your baby is developing | How your body is changing

How your baby is developing

Your baby is getting ready to start life in the real world. Babies born at 37 weeks are not premature, just a little early. Your baby will be around 36cm long and weigh around 3,400g, but this is only a guide as some babies can be very long and some can weigh a lot. Generally, boy babies weigh more than girls and are often longer.

By the time she is born, your baby will have lots of fat to keep her warm and make her cuddly. About 16% of her body will be made up of fat.

Babies have characteristics you can easily overlook. They have little chests that seem to stick out and tiny breast buds. They often have long fingernails, which need cutting to stop them scratching themselves. Some are born with a complete hairstyle, others are practically bald. If your baby's eyes are blue, they may darken as pigment develops over the first few months. If your baby has brown eyes, they won't get lighter. Pigment is only added, not removed.

Your baby will have been developing her own routine. This, of course, is nothing like your routine. In the last six weeks in the womb your baby is either active or quiet. She will be in an active state for up to 70% of the time. The quiet moments last from between 15 to just over 20 minutes. While your baby is being active she will be moving her legs and arms, her heart rate will go up and she will be making breathing movements. When she is quiet she won't be doing any of these things and her heart rate will stay the same. Who knows what she's doing when she is quiet? Your baby's eyes will be open when she is awake and shut when asleep.

The first breath is a big shock for your baby and she will be practising for this moment right up until birth. This practice is essentially breathing underwater as she is surrounded by amniotic fluid. Her lungs are pretty mature now but will still develop and grow tiny air sacs long after birth. In the last few weeks before birth, they make lots of surfactant - the fatty substance that keeps the tiny airways open - which helps them take in as much oxygen as possible.

Your baby will hiccup a lot around this time, as the amniotic fluid she is breathing in will sometimes tickle her throat. Your baby will be learning how to coordinate things so she can suck, swallow and breathe at the same time.

Your baby's bones are getting harder but some of her skull bones will stay soft to help her get down the birth canal. The soft parts of the skull mean your baby's head has some give in it as it pushes out through the birth canal.

By now your baby has less and less room. The amniotic fluid that has been cushioning her in your womb has fallen from 800ml at 32 weeks to 500ml. Meanwhile, the placenta at birth will weigh about 450g - around one seventh of the weight of your baby. Your immunity to various infections will have been transferred (as antibodies) through the placenta to your baby, and if you go on to breastfeed your baby then your milk gives her more antibodies. Your baby's gums will be quite hard when she's born yet, remarkably, soon her tooth buds will push teeth through them.

After 40 weeks, your baby has done all the work and is now ready to live without your womb and the life support your body has been providing. But don't expect her to be happy about it. Many babies are pretty miserable until they get used to having to do all the things for themselves that you did. If you think about it, that includes eating, going to the toilet (both sorts), regulating body temperature and breathing. So be patient.

However excited you are about having your baby, think of things from her point of view. Don't expect her to be grateful to you for having her for at least, oh, 20 years.

How your body is changing

• Shortness of breath

You can be short of breath early on in pregnancy because hormones (progesterone) affect your breathing. Progesterone makes you breathe more deeply and makes you more aware of breathing. As your baby gets bigger, you can feel short of breath because your diaphragm is pushed up and your lungs have less room to suck air in. This can mean you take more shallow breaths and feel breathless. You can't do much about it but don't panic, just relax. You are getting enough breath in and if you start breathing faster you will feel dizzy and get tingling in your fingers.

Sometimes, being short of breath can be a sign of more serious problems such as a blood clot in your lungs or a chest infection. If you feel unwell, are coughing or have a fever or chest pain see your midwife or doctor straight away. Likewise, if the shortness of breath is bad you should also see your midwife or doctor.

• Stress incontinence

When you're heavily pregnant, everything in the lower part of your body feels a bit precarious, like it's all trying to escape. Stress incontinence means you leak urine when you laugh or strain, or even if you get up and walk. It's annoying and can be a real problem if you leak a lot. The problem is caused by the baby inside your large muscular womb pressing on your bladder. This puts pressure on the valves guarding the bladder's exit, and so urine leaks out. That said, you need to make sure (with your midwife or doctor's help) that you don't have a urinary infection or some other medical problem.

The problem usually gets better after you give birth. However, many women are left with some stress incontinence because giving birth plays havoc with your pelvic floor muscles. Normally, these pelvic muscles form a sling around the bladder neck and help keep the exit closed but giving birth can give them quite a battering. You could ask your midwife about pelvic floor exercises to help things.

As you wait for your special delivery, read up on and talk to other women and your midwife about labour. It's great to know what sort of labour you would like, but try not to feel disappointed, guilty or upset if things don't go according to plan.

Remember, there are no rewards for bravery in labour, so don't feel bad about asking for pain relief.

Please do your best to breastfeed longer than 48 hours. We have one of the lowest rates in Europe and we can't just be genetically bad at it. It isn't always easy and it isn't always a pleasure, but it is best for your baby. The tiny miserable bits of colostrum that come out of your breasts for the first few days really are enough for your baby. She hasn't eaten anything for nine months remember - she won't come out ravenously hungry because she has never had a square meal.

Your baby IS getting enough to eat. It may be miserable, need a poo, and hate being born but it is not starving. It will do just fine until the milk comes in. Enough ranting. Enjoy your new baby and make sure everyone you know helps you as much as possible afterwards.

Remember, you can chat to other mums about all the 'joys' of pregnancy on our Pregnancy Talk boards. And once your baby is born, get posting on the Talk forums in Being a parent.

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