Brain damage from hyponatraemia (low blood sodium)

Any condition which disrupts the fluid balance in the body can lead to hyponatraemia. In pregnancy and childbirth, women are more vulnerable to hyponatraemia from fluid imbalance (or water intoxication) owing to a combination of factors which affect their body fluids at this time:

• In pregnancy a woman’s blood circulation naturally increases in volume to provide blood, nutrients and oxygen through the placenta to the unborn baby. This reduces the balance between fluid and sodium in her blood. This naturally increases her risk.
• In the third trimester (final three months) of pregnancy, many women experience urine retention which means that less water is passed out of the body. 
• In labour, the body naturally produces a hormone called oxytocin. This hormone stimulates contractions in the uterus that are necessary for the woman to give birth. Oxytocin is a natural anti-diuretic which further reduces the woman’s ability to urinate and pass water. 
• If contractions in labour are too weak or slow for labour to be effective, the woman may be given a drug which is very similar to the body’s natural oxytocin. This drug is often known by its trade name, Syntocinon. When a woman is given Syntocinon in labour, this has the same anti-diuretic (water-retaining) effect as oxytocin. Syntocinon is given by a drip with additional intravenous (IV) fluids. This increases the woman’s fluid levels even further. 
• During the hard work of labour, the woman may be encouraged to drink plenty of water to avoid dehydration. Even where the midwife is noting the woman’s fluid input and output, this additional low-salt fluid intake from drinking water can be missed. A research study into hyponatraemia in labour found that, even amongst low-risk women who hadn’t been given Syntocinon or IV fluid, more than a quarter of women who drank more than 2.5 litres of fluid in labour were hyponatraemic. 

Hyponatraemia in pregnancy and childbirth is also dangerous for the baby. The child is at additional risk of severe brain injury if the mother has no symptoms, or her early symptoms are mistaken for other pregnancy-related conditions, leaving her hyponatraemia undiagnosed. Throughout pregnancy the fetus (unborn baby) shares the mother’s blood circulation and may suffer injury as a result of the mother’s hyponatraemia before the mother shows any symptoms and the condition is diagnosed.