Need to talk? Call 1800 882 436.
It's a free call with a maternal child health nurse. *call charges may apply from your mobile

Is it an emergency? Dial 000
If you need urgent medical help, call triple zero immediately.

beginning of content

Anatomy of pregnancy and birth

6-minute read

What happens during conception?

Conception occurs when a woman’s ovum (egg) is fertilised by a male’s sperm. All of the baby’s genetic characteristics are decided in that instant. A woman is pregnant from the moment of conception, but pregnancy is measured in weeks – starting from the first day of the mother’s last menstrual period.

Although you may not feel a change straight away, your body will begin to change immediately. For example, levels of a hormone called human chorionic gonadotropin (hCG) will begin to rise very soon after conception. An elevated level of hCG will help confirm a pregnancy, and it shows up in either using a home pregnancy test or with a blood test done by a doctor.

Read more about the early signs of pregnancy here.

Diagram showing the female reproductive system.
Illustration showing the female reproductive system.

What physical changes occur in early pregnancy?

For many women, the first physical sign of pregnancy is a missed period. But there are many other changes happening to the mother's body in the early months:

  • Hormonal changes: hormonal changes are essential in pregnancy and help ensure your baby's growth and development. Hormonal changes may, however, also trigger nausea or vomiting (commonly referred to as 'morning sickness'), changes in the look or feel of the breasts, or feelings of tiredness or moodiness.

  • Changes to your breasts: not all women experience breast changes, but you might notice your breasts get larger, feel sore or tender, or your nipples might become darker.

  • Increased need to urinate: early in pregnancy, the amount of blood in the mother's body increases. This causes the mother's kidneys to process more fluid, resulting in an increased need to urinate. As the womb (uterus) grows to accommodate the growing baby, there is also more pressure on the bladder, leading to a need to urinate more often.

  • Some weight gain: with fuller breasts, a growing uterus and increased blood volume, a small amount of weight gain is to be expected. A pregnant woman may gain 1 to 2 kilograms in her first trimester.

  • Changes to the cervix: the cervix is a muscular cylinder at the bottom of the uterus. From conception until late in pregnancy (just before birth), the cervix protects the growing baby by increasing in size and strength.

How does your body change over the course of the pregnancy?

As pregnancy progresses, more obvious physical changes appear, including the appearance of the 'baby bump'.

  • Abdominal muscles: the mother's abdomen constantly changes shape during the pregnancy as the baby grows and moves. The abdominal muscles gradually stretch as the womb expands during pregnancy.

  • Skin changes: hormonal changes may affect the skin. For example, a pregnant woman may get acne, or existing acne may worsen. Some women notice patches of darker skin on the face (called chloasma); these will fade after the baby is born. Stretch marks may also appear, particularly if there is weight gain.

  • Weight gain: further weight gain is caused mainly by the growing baby, increased amounts of amniotic fluid (the protective liquid within the uterus that surrounds the baby), and the increased size of the uterus and placenta.

How does your body prepare for childbirth?

Physical changes in the third trimester help prepare a woman's body for birth.

  • Pelvis: the pelvis of a pregnant woman changes throughout pregnancy, including changes to its shape, how it sits within the body, and how the joints and ligaments behave. The joints and ligaments of the pelvis relax during pregnancy to accommodate the growing baby. As the due date approaches, the pelvis expands to create space for the baby travel through the birth canal during birth.

  • Uterus: the muscles of the uterus may occasionally tighten in preparation for labour, which are commonly referred to as Braxton Hicks contractions. These 'false' or practice contractions are irregular, not usually painful (but may be uncomfortable) and tend to occur more often and feel stronger closer to the baby's due date.

  • The 'show': the cervix may softens and dilates (opens) to prepare for the baby's passage through the birth canal. As the cervix opens, the vagina might release a clear, pink, or slightly bloody discharge (sometimes referred to as the 'show'). This is the release of the mucous plug that sits over the cervix during pregnancy, and may signal that labour is approaching.

  • During active labour, the muscles of the uterus contract purposefully, to help the baby move down into the birth canal. Each labour contraction may start like a wave and build in intensity, moving from the top of the uterus right down to the cervix. Your uterus will feel tight during the contraction. But between contractions, the pain may ease off and allow you to rest before the next one builds.

Read more about what happens to your body during child birth.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: October 2020

Back To Top

Call us and speak to a Maternal Child Health Nurse for personal advice and guidance.

Need further advice or guidance from our maternal child health nurses?

Healthdirect Australia acknowledges the Traditional Owners of Country throughout Australia and their continuing connection to land, sea and community. We pay our respects to the Traditional Owners and to Elders both past and present.

This information is for your general information and use only and is not intended to be used as medical advice and should not be used to diagnose, treat, cure or prevent any medical condition, nor should it be used for therapeutic purposes.

The information is not a substitute for independent professional advice and should not be used as an alternative to professional health care. If you have a particular medical problem, please consult a healthcare professional.

Except as permitted under the Copyright Act 1968, this publication or any part of it may not be reproduced, altered, adapted, stored and/or distributed in any form or by any means without the prior written permission of Healthdirect Australia.