By PPH Foundation

After a baby is born, the uterus has one of the most important jobs in childbirth: to contract firmly. These powerful contractions compress the blood vessels that supplied the placenta during pregnancy, helping stop bleeding and protecting the mother from postpartum haemorrhage, PPH.

This process is driven by oxytocin, a hormone naturally released during labour, childbirth and breastfeeding. Oxytocin binds to specialised receptors on the muscles of the uterus, triggering rhythmic contractions that shrink the uterus and seal the blood vessels where the placenta was attached. As pregnancy progresses, the number of oxytocin receptors increases, preparing the uterus for labour and the critical minutes after birth.

Sometimes, however, the uterus fails to contract effectively, a condition known as uterine atony. It is the leading cause of postpartum haemorrhage worldwide. When the uterus remains relaxed, blood vessels stay open, allowing severe bleeding that can become life-threatening within minutes.

Several factors increase the risk of uterine atony. A prolonged or difficult labour can exhaust the uterine muscles, reducing their ability to contract after delivery. Carrying twins or a large baby, or having excessive amniotic fluid, can overstretch the uterus, making it less responsive to oxytocin. Previous episodes of postpartum haemorrhage, infection and certain medications may also interfere with normal uterine contractions.

Dr Kireki Omanwa, President of the Kenya Obstetrical and Gynaecological Society and Co-Lead of the End PPH Initiative, explains:

"The uterus is nature's first defence against postpartum haemorrhage. Every effective contraction helps close the blood vessels left behind after the placenta is delivered. When those contractions fail, healthcare providers must act immediately with evidence-based interventions to restore uterine tone and prevent severe blood loss."

Healthcare providers reduce the risk of uterine atony through Active Management of the Third Stage of Labour, which includes administering a recommended uterotonic immediately after birth, careful monitoring of uterine tone and early recognition of excessive bleeding. Prompt treatment with uterotonics, tranexamic acid where indicated, uterine massage when appropriate, and other emergency interventions can prevent complications and save lives.

Understanding how the uterus works reminds us that preventing postpartum haemorrhage begins with supporting the body's natural mechanisms while ensuring that every birth is backed by skilled care and timely intervention.

References

World Health Organization. WHO Recommendations for the Prevention and Treatment of Postpartum Haemorrhage. Geneva, 2023.

American College of Obstetricians and Gynecologists. Practice Bulletin No. 183: Postpartum Hemorrhage. Obstetrics & Gynecology. 2017.

FIGO. FIGO Recommendations on the Management of Postpartum Haemorrhage. International Journal of Gynecology & Obstetrics. 2022.

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