Anatomy of pregnancy and birth

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

You are pregnant from the moment of conception. 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. Soon after you have conceived a baby, levels of a hormone called human chorionic gonadotropin (hCG) begin to rise.

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.

For many people, the first physical sign of pregnancy is a missed period. 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

You may notice that your breasts become larger or feel sore or tender. Your nipples may also become darker. Not all people experience breast changes.

Increased need to urinate

You may notice an increased need to urinate (wee) in your pregnancy. This is caused by hormonal changes in early pregnancy.

Later in 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.

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

Abdominal muscles

Your abdomen 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 notice:

• patches of darker skin called melasma on your face that will fade after your baby is born
• you suddenly develop acne, or if you already have acne, it may get worse
• stretch marks as you put on weight

Weight gain

During pregnancy, there are many different reasons why you will gain weight, such as:

• your growing baby
• 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 (the way that you walk)

Your gait 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

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

Pelvis

Throughout your pregnancy, your pelvis changes.

The pregnancy hormone relaxin makes the joints in your pelvis more mobile. This is to accommodate your growing baby and make it easier for your baby to travel through your birth canal.

Uterus

Throughout your 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 usually they are not painful (but may be uncomfortable). They occur more often and feel stronger closer to your baby's due date.

The cervix and the 'show'

During your pregnancy, your cervix is long and closed. As childbirth approaches, your cervix starts to soften and dilate (open) to prepare for your baby going through your birth canal.

• The Royal Australian and New Zealand College of Obstetricians and Gynaecologists has an informative handout to help prepare you for labour and birth.
• The Royal Women's Hospital has a handout addressing common concerns you may have in early pregnancy.
• The Centre of Perinatal Excellence (COPE) provides emotional support and tips to look after yourself for people expecting a baby and new parents.
• Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 or video call. Available from 7 am to midnight (AET), 7 days a week (including public holidays).

Looking for information for Aboriginal and/or Torres Strait Islander people?

• You can find out more about Aboriginal and/or Torres Strait Islander pregnancy health on Stronger Bubba Born or watch the How to Have a Safer Pregnancy video.

Looking for information for sexually and gender-diverse families?

• The Gidget Foundation Australia provide perinatal support to sexually and gender-diverse families.