What is the pelvis?

The pelvis is located in the middle of the human body, below the abdomen and above the thighs. It comprises the bony pelvis — which includes the hip bones —, pelvic cavity, pelvic floor, and perineum — the area of skin between the opening of the vagina and the anus. The bones around the pelvis are attached by several ligaments, comprised of tough and flexible tissue, and four joints. These help the pelvis to function.

What does the pelvis do?

The pelvis has many roles, including holding the body upright so you can stand, walk and run. Additionally, a woman’s pelvis, which is wider, more rounded and has thinner bones than a male’s, helps women through pregnancy and childbirth.

How does the pelvis change during pregnancy?

A pregnant woman’s pelvis changes through pregnancy. Its shape, position, and joint and ligament behaviour adjust to support the baby during pregnancy, making childbirth easier for both mother and baby. For example, a hormone named relaxin helps the pelvis relax during pregnancy and birth to accommodate the growing baby and to allow for an easier delivery.

Pelvic pain — a common condition in pregnancy

While changes to a pregnant woman’s pelvis help facilitate pregnancy and birth, they can cause discomfort. For instance, when the joints of the pelvis relax, a pregnant mother can feel less stable on her feet, and she may feel discomfort in her pelvis and lower back pain.

The following approaches have been shown to reduce pregnancy-related pelvic pain:

• applying heat packs to painful areas
• wearing low-heeled shoes
• avoid standing on one leg (sit down to get dressed, climb stairs one at a time)
• seeing a physiotherapist for exercise and posture advice
• avoiding standing or walking for long periods of time
• being careful about movements that stretch the hip, such as getting in and out of cars, sitting on low stools and squatting

Although very rare, other injuries to the pelvis can occur during pregnancy and childbirth, including fractures. A pelvic injury such as a fracture requires prompt medical attention.

The pelvis and childbirth

For birth, a baby should ideally be positioned with their head down and facing the mother’s back. This position helps the baby descend through the pelvis and birth canal.

A baby who lies bottom or feet down in the pelvis during late pregnancy is said to be in breech position. Breech presentations increase the chance of a complicated vaginal birth and can lead to a caesarean section. While most babies naturally turn in the womb in time for labour, techniques performed by an obstetrician, such as an external cephalic version (ECV), can help the baby to turn.

Most babies naturally get into the 'head down' position in time for labour and birth. Certain positions for birth can help guide the baby down through the pelvis. For example, staying upright during contractions means that gravity is working to help the baby transition through the pelvis, and along the birth canal.

There are other ways to take advantage of the structure and function of the pelvis to assist in childbirth. Read more about positions for labour and birth.