A normal pregnancy lasts for between 37 and 42 weeks, an average of 40 weeks. The period of pregnancy, or gestation, is divided into three trimesters. It's a useful way to help describe the changes that happen during pregnancy. The first trimester is week one to week 12, the second is week 13 to week 27, and the third is week 28 to week 40. In the first trimester, your baby’s body and organs develop, in the second trimester, your baby’s organs mature and in the third trimester, your baby gets bigger and lays down stores of fat.
One of your ovaries releases an egg around 14 days before your period. This is called ovulation. It's usually in the middle of a 28-day menstrual cycle, but can be later if you have longer cycles and earlier if your cycle is shorter. The egg can be fertilised by sperm in one of your fallopian tubes. Conception occurs when the fertilised egg travels along the tube and implants in your womb (uterus) about six days after fertilisation. The fertilised egg grows and is called an embryo.
When you become pregnant, your womb doesn't shed its lining as it normally does at the end of a menstrual cycle, so you don't have a period each month. A missed period is one of the early signs of pregnancy.
You can buy a pregnancy test from a pharmacy or supermarket. This can test for pregnancy from the first day of a missed period. Some testing kits can give a result even before you miss a period. Your GP or family planning clinic can also arrange a pregnancy test for you.
During the first trimester, the changes in your hormones cause various changes to your body.
As well as a missed period, you might have other early symptoms of pregnancy, including breast tenderness. You may also need a larger, more supportive bra. Your nipples and the surrounding area (areola) may become larger and darker. You may need to pass urine more often because your growing womb starts to press on your bladder, and the hormonal changes may make you feel very tired.
Many women feel sick, and some will vomit in early pregnancy. This nausea and vomiting is often called morning sickness although it can happen any time or throughout the day. The cause is unknown, but research suggests it may be related to high levels of pregnancy hormones. There are things you can do to try and reduce the nausea and sickness: get plenty of rest, eat little and often, and avoid smells and tastes that make you nauseous. If you can't keep food or fluid down, see your GP or maternal and child health nurse.
You may become constipated because the rising hormone levels slow your bowels down. To relieve this, drink plenty of fluids and eat a healthy diet with plenty of fibre. Heartburn is also common. Talk to your pharmacist or GP about what you can do and what’s safe for you to take for relief from heartburn.
Throughout this trimester or as soon as you know that you’re pregnant (and preferably beforehand), you should be taking at least 400 micrograms (0.4mg) folic acid daily. This is the period when your baby's brain and nervous system are developing and folic acid reduces the chance of the baby being born with a spinal cord problem called a neural tube defect (NTD), such as spina bifida. If you're at a high risk of having a baby with a NTD, your doctor will prescribe a much higher dose of 5000 micrograms (5mg) folic acid daily.
Drinking alcohol during pregnancy can affect the development of your baby’s brain and slow down physical growth. This can result in a low birth weight plus lifelong physical and behavioural problems. It is best to avoid alcohol during pregnancy. This is especially important during the first three months when important organs including the brain are forming. For support and advice on stopping alcohol consumption during pregnancy, speak frankly with your doctor or maternal and child health nurse.
Your baby grows and develops quickly in the first trimester. By the time you are 10 weeks pregnant (eight weeks after fertilisation) all the body parts are present, if not quite fully developed, and the placenta is fully formed. At this point, the embryo is known as a foetus. Nutrients are transferred from you to the baby through the placenta. Waste products from the baby are returned to your circulation to be removed.
By the time you are 12 weeks pregnant (10 weeks after fertilisation) your baby is approximately 60mm long. At this stage, your baby's forehead grows with the developing brain, the eyelids are still sealed shut and the ears are forming.
Your pregnancy will start to show during the second trimester although when this happens varies from woman to woman.
Any sickness or nausea usually gets better by the time you’re 16 to 20 weeks pregnant. You may get backache, hip pain or pelvic pain because pregnancy hormones cause your ligaments and tendons to relax, and your posture may change as your baby grows.
You may first feel the baby move around 18 to 20 weeks, but this varies between women and may be a few weeks earlier if it's not your first pregnancy. The movements become much more vigorous and obvious as the baby gets bigger and stronger.
In the second trimester, your baby's organs mature and its skeleton starts to harden. The baby swallows amniotic fluid and passes it out through its gut. The kidneys start to work and pass small amounts of urine.
By 19 weeks your baby is able to hear, and is covered in fine hair called lanugo. If you have a scan at this stage, it's often possible to find out the baby’s gender. By the end of the second trimester, your baby has a chance of surviving if born prematurely, but would need intensive care.
As your abdomen and breasts grow, you may get stretch marks. These are harmless and usually fade after the baby is born. You may find the extra weight you are carrying makes you tired, and you may get breathless as your expanded womb makes your lung capacity smaller.
Some women have trouble finding a comfortable position to sleep in. Your baby's head drops down into your pelvis (engages), getting ready for delivery — for a first baby this will usually happen toward the end of the pregnancy (around 37 weeks onwards). This can cause pressure on your bladder and you may need to pass urine more often. If you’ve had a baby before, the head may not engage until labour.
Braxton Hicks contractions (practice contractions) can start in the second trimester, but are much more likely in the third. These can be mistaken for labour but the difference is that real labour contractions will continue to occur regularly. Braxton Hicks contractions only last about 25 seconds.
Your baby's lungs mature throughout the third trimester and by 32 weeks your baby is much more likely to survive if born prematurely. Your baby makes breathing movements, even though the lungs don't work properly until birth. Fat stores are laid down in preparation for birth. Your baby grows fine hair and fingernails, the eyes open and close, and teeth may start growing under the gums.
Weight gain is a normal part of pregnancy - the exact amount varies from woman to woman. Your midwife will weigh you at your first appointment. Unless you are very overweight or very underweight, your midwife probably won't weigh you again because it doesn't necessarily give any useful information about your developing baby.
If you're concerned about your weight gain, talk to your midwife or GP. They’ll be able to tell you whether it’s too much or too little for you and your baby.
The weight you gain during pregnancy isn't the same as getting fat. The extra weight should be made up of:
Health Direct Australia: Pregnancy Birth and Baby
Helpline 1800 882 436
Arulkumaran S, Symonds I M, and Fowlie A, Oxford handbook of obstetrics and gynaecology. Oxford: Oxford University Press, 2004
Chang MY, Chen CH, and Huang KF. Effects of music therapy on psychological health of women during pregnancy. J Clin Nurs, 2008; 17(19):2580-87
Department of Health (UK). The Pregnancy Book 2009. [online] Whitehall, London: Department of Health. Oct 2009 [accessed 30 Jun 2011] Available from: http://www.dh.gov.uk/
Greer I. Pregnancy: The Inside Guide. London: Collins, 2003
Hammer RL Perkins J Parr R. Exercise during the childbearing year. Journal of Perinatal Education. 2000; 9(1): 1–14.
Johnson M, Chang A, Breart G, et al. Turnbull's obstetrics. 3rd ed. Churchill Livingstone, 2001
McGrail A and Metland D. Expecting: Everything you need to know about pregnancy labour and birth. London: Virago Press, 2004
National Health and Medical Research Council. Australian Guidelines: To Reduce Health Risks from Drinking Alcohol. Canberra, ACT: Commonwealth of Australia. 2009 [accessed 19 Aug 2010] Available from: http://www.nhmrc.gov.au/_files_nhmrc/file/publications/synopses/ds10-alcohol.pdf (PDF, 2.3Mb)
National Institute for Health and Clinical Excellence (NICE). Antenatal care: routine care for the healthy pregnant woman. [online] 2008 [Last reviewed May 2011, accessed 30 Jun 2011] Available from: http://guidance.nice.org.uk/CG62
Oats J and Abraham S. Fundamentals of obstetrics and gynaecology. 8th ed. London: Elsevier Mosby, 2005
Sports Medicine Australia (SMA). Exercise in pregnancy. [online] Mitchell, ACT: SMA. [accessed 18 Aug 2010] Available from: http://sma.org.au/wp-content/uploads/2009/10/WIS-ExPreg.pdf (PDF, 688Kb)
This information has been developed and reviewed for Bupa by health professionals. To the best of their knowledge it is current and based on reputable sources of medical research. It should be used as a guide only and should not be relied upon as a substitute for professional medical or other health professional advice.
Bupa Australia Pty Ltd makes no warranties or representations regarding the completeness or accuracy of the information. Bupa Australia is not liable for any loss or damage you suffer arising out of the use of or reliance on the information. Except that which cannot be excluded by law. We recommend that you consult your doctor or other qualified health professional if you have questions or concerns about your health. For more details on how we produce our health content, visit the About our health information page.
Last Published: 30 July 2011