Anatomy of pregnancy and birth

What happens during conception?

Conception occurs when an ovum (egg) is fertilised by sperm.

You are pregnant from the moment of conception, but pregnancy is measured in weeks, starting from the first day of your last period.

Although you may not feel a change straight away, your body will begin to change immediately. Levels of a hormone called human chorionic gonadotropin (hCG) begin to rise soon after conception.

A higher level of hCG can be used to confirm a pregnancy. It shows up in home pregnancy tests and blood tests organised by your doctor.

What changes occur in early pregnancy?

For many people, the first physical sign of pregnancy is a missed period. But there are many other early signs of pregnancy.

Hormonal changes

Hormonal changes are essential in pregnancy and help ensure your baby's growth and development.

Hormonal changes may also trigger:

• nausea or vomiting (commonly referred to as 'morning sickness')
• changes in the look or feel of your breasts
• feelings of tiredness
• constipation

Changes to your breasts

Not all people experience breast changes. But you might notice that your breasts get larger or feel sore or tender. Your nipples might also become darker.

Increased need to urinate

You may notice an increased need to urinate in your pregnancy. This is partly due to your body making more urine (wee) than usual. It is also caused by hormonal changes in early pregnancy.

As your uterus (womb) grows to accommodate your growing baby, there is more pressure on your bladder. This causes you to need to urinate (wee) more often.

How will my body change over the course of the pregnancy?

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

Abdominal muscles

Your abdomen constantly changes shape during pregnancy as your baby grows and moves. Your abdominal muscles gradually stretch as your womb expands during pregnancy.

Skin changes

Hormonal changes may affect your skin. You may get acne, or existing acne may get worse.

Some people notice patches of darker skin on the face (called chloasma); these will fade after your baby is born.

Stretch marks may also appear, as you put on weight.

Weight gain

Weight gain during pregnancy is caused mainly by:

• your growing baby
• increased amounts of amniotic fluid (the protective liquid within your uterus that surrounds your baby)
• the increased size of your uterus
• the placenta
• additional breast tissue
• increased blood volume
• increased fat storage

Gait

Your gait (the way that you walk) can change as your pregnancy progresses. Your gait may change due to your:

• centre of gravity changing with your growing uterus and weight gain
• joints becoming more mobile
• abdominal muscles weakening as your ‘baby bump’ increases in size

How does my body prepare for childbirth?

Physical changes during pregnancy also help prepare your body for birth.

Pelvis

Your pelvis changes throughout pregnancy, including how it sits within your body and how your joints and ligaments behave.

The joints and ligaments of your pelvis relax and become more mobile during pregnancy. This is to:

• accommodate your growing baby
• make it easier for your baby to travel through your birth canal

The increased mobility of your joints is due to the pregnancy hormone relaxin. This hormone can affect other joints in your body as well.

Uterus

During pregnancy, your uterus occasionally tightens in preparation for labour. These ‘practice contractions’ are commonly referred to as Braxton Hicks contractions.

Braxton Hicks contractions are irregular and aren’t usually painful (but may be uncomfortable). They tend to occur more often and feel stronger closer to your baby's due date.

What are some of the changes in my body during childbirth?

Your cervix undergoes dramatic changes during labour. It changes from long and firm to soft, thin and more elastic. Your cervix also dilates (opens). Changes to your cervix are partly triggered by contractions of your uterus, which help open the cervix.

The uterus

During active labour, the muscles of your uterus contract purposefully, to help:

• open your cervix
• help your baby move down into the birth canal.

Each labour contraction may start like a wave and build in intensity, moving from the top of your uterus right down to your cervix. Your uterus will feel tight during the contraction. But between contractions, the pain intensity may ease off and allow you to rest before the next one builds.

Read more about what happens to your body in childbirth.