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The first 3 months of pregnancy – the first trimester

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During the first 12 weeks or 3 months of your pregnancy, you will usually only put on about 1 or 2 kilos, or possibly less if you have morning sickness. Most of this weight is in the placenta (the afterbirth) and in your breasts, uterus and in the extra blood your body will make.

  • During pregnancy your body works harder, your heartbeat and breathing rate are faster.
  • Hormones may make your breasts become tender to the touch, and become larger and heavier.
  • Your uterus will get bigger and put pressure on your bladder so that you need to urinate (pass water) more often.

This section provides you with a week by week summary of what is happening to your body and to your baby. Don't worry if you think you are different from the week by week stages in this section, as each woman will experience her pregnancy slightly differently.

There are two more topics which have information about the next two stages of your pregnancy.

Towards the end of your pregnancy you might like to look at the topics in the section The birth.

Always discuss any concerns or worries you may have during your pregnancy with a doctor or midwife. You may also like to link to other parts of this site to find more information on some of the issues that are important during you first trimester (3 months).

For more information you could look in the section 'Staying well' on this website.

More information

There is more detailed information about the development of a baby and the changes for a pregnant woman on:

The Raising Children Network site

There is also a section for fathers on the Raising Children Network site

Pregnancy, birth and baby

Week 3

  • You
    Each week of your pregnancy is numbered by the amount of weeks from the first day of your last period. This means that if you have a regular four week cycle, week 3 of your pregnancy will actually be the first week after your baby was conceived. At this stage, you will not have missed your period and won't know if you are pregnant.
  • Your baby
    During week 3 the fertilised egg burrows into the lining of your uterus and is the size of a full stop.

Week 4

  • You
    During week 4, you still haven't missed your period, but if you have been trying to conceive (get pregnant) you will probably be feeling very excited as you wonder if you have been successful this month.
  • Your baby
    Specialised layers of cells are beginning to develop, which will form your baby's vital organs, nervous system, bones, muscles and blood.

Week 5

  • You
    By week 5, your period is late so you may begin to think that you could be pregnant and you may notice that your breasts are slightly bigger and tender to touch. But you may simply feel as if your period is about to start (some women have called the first couple of weeks of pregnancy the 'longest stretch of PMS they have ever experienced'!).

    As soon as your period is a day late, you can do a urine pregnancy test. You can go to a doctor for a pregnancy test or you can buy a pregnancy testing kit from your pharmacy.

    Some women may have already experienced nausea and vomiting by this time. This is known as morning sickness but can actually happen at any time of the day or night. The severity of morning sickness and how long into the pregnancy it lasts varies a great deal from one woman to another. For most women who do get morning sickness, the problem usually improves greatly by the end of the first three months, if not sooner. Go to the topic Morning sickness for more information.
  • Your baby
    At week 5, your baby is about 2 mm long. Your baby's spine, brain, muscles and bone are already starting to form.

Week 6

  • You
    You may be feeling very tired at this early stage of your pregnancy. Gentle, regular exercise such as swimming or walking will help you to feel less tired and more able to cope with the demands that your pregnancy is making on your body. Have a look at the topic Exercise in pregnancy.
  • Your baby
    By the end of this week, your baby (called an embryo) has a heartbeat. Blood is pumping around the baby and out along the umbilical cord to the placenta. The placenta is an organ that acts as a filter. It allows oxygen and nutrients to pass to the embryo, and carbon dioxide and waste products to be eliminated. The placenta is also called the afterbirth.

    Your baby's head and body are now defined and tiny buds appear where arms and legs will develop. Your baby is now about 6 mm long - about the length of a grain of rice.

Week 7

  • You
    Some women find that they are quite emotional during these early weeks of pregnancy - this is caused mainly by pregnancy hormones.

    Some women may notice that their breasts are bigger now and the area (areola) around their nipples has darkened. You may see large 'goose bumps' forming around the areola (called Montgomery's tubercules) and your nipples may become larger.
  • Your baby
    Your baby's spinal cord and brain are developing and your baby lies within a sac of membranes and is supported by fluid known as amniotic fluid. Nostrils and lips now appear on your baby's face and the eyes can be seen under the skin.

Week 8

  • You
    You may find that you have gone off certain foods that you used to like. Some women also have a taste like metal in their mouth, which is probably caused by pregnancy hormones. As your uterus is growing, you may need to urinate (pass water) more often because of the increased pressure on your bladder.

    Many women notice that they have more vaginal discharge at this stage. This is quite normal, unless the discharge is itchy, uncomfortable or has an unpleasant smell. If your discharge is causing you concern, speak to your doctor or midwife, as this may be a sign of a vaginal infection or thrush. Thrush is a common problem during pregnancy, but can be easily treated. For more information, have a look at the section on vaginal thrush in the topic Common health problems in pregnancy.
  • Your baby
    The baby now looks more human - your baby's limbs can be seen and hands and feet are taking shape … all this amazing growth, yet your baby is now around just 1.3 cm long!

Week 9

  • You
    Many people talk about 'the glow of pregnancy', referring to the way a pregnant woman's skin looks. This glow is caused by an increase in oil on skin due to pregnancy hormones. But not all women feel this glow, and some may notice pimples because of this extra oil. Some women have the opposite problem and their skin becomes very dry. Either way, make sure you drink plenty of water (6–8 glasses per day) which will help your skin.
  • Your baby
    At the end of this week, your baby is now called a fetus, not an embryo. The limbs are growing quickly and the fingers and toes are forming. Your baby's skeleton, which started as cartilage, is now changing to bone.

Week 10

  • You
    You may find that your clothes are getting tighter around your waist and breasts. Your abdomen may look bigger, but at this stage it is often due to changes in your bowel (rather than your uterus getting bigger) and is nothing to worry about. Your uterus is now about the size of an orange and is still hidden within your pelvis.
  • Your baby
    Your baby is now about 2.5 cm long and has tiny fingers and toes.

Week 11

  • You
    Some women find that constipation is a problem during pregnancy. Pregnancy hormones relax the bowel, which means that bowel motions don't pass through as quickly. Increasing the fibre in your diet and drinking plenty of water will usually help. If you are still having problems, talk to your doctor, midwife or pharmacist about bulking laxatives that are suitable to use during pregnancy. For more information see the section on constipation in the topic Common health problems in pregnancy.
  • Your baby
    Your baby's internal organs are now all formed - including ovaries or testicles.

    (Click on image to enlarge)

Week 12

  • You
    Often by now morning sickness is much less of a problem and you are probably feeling less tired. Your uterus is continuing to grow and is higher than your pelvis.
  • Your baby
    Your baby's head is becoming more rounded and the eyelids have formed and closed over the eyes. You still can't feel it, but your baby is moving around constantly in your amniotic fluid - your baby can now roll, stretch, yawn and wriggle fingers.

    From this stage on your baby's heartbeat may be able to be heard with a fetal heart detector.


The Raising Children Network, a comprehensive Australian resource for expectant parents and parenting newborns to teens, has developed a resource for fathers to be which provides information on a range of issues related to pregnancy and fatherhood.

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The information on this site should not be used as an alternative to professional care. If you have a particular problem, see your doctor or midwife.


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