Researchers have discovered that it is possible to drink too much water during childbirth.
If too much water is consumed, the woman may develop hyponatraemia, or lack of sodium in the blood. This can lead to irritability, headaches, nausea and vomiting. If not treated by the excess water being removed, it can cause cerebral oedema, or swelling of the brain, resulting in convulsions or even coma.
The condition may be difficult to diagnose during labour because the early symptoms can be mistaken for pre-eclampsia.
A study was carried out by Dr Vibeke Moen of the Karolinska Institute, Sweden, and colleagues. They recruited 287 pregnant women who were allowed to drink freely during their labour. Blood samples were taken before and after delivery, and cord blood samples taken after the birth.
Of the women, 61 (21 per cent) consumed more than 2.5 litres of fluid during labour, and of these, 16 (26 per cent) developed hyponatraemia (a plasma sodium level of less than 130mmol/litre).
A reduced plasma sodium level was linked to a longer second stage of labour and increased need for assisted labour or caesarean. Findings are published in BJOG: An International Journal of Obstetrics and Gynaecology.
The authors warn that hyponatraemia is fairly common after labour, as the ability to deal with fluid overload, or "water load tolerance", is temporarily reduced. They call for guidelines to be set on safe levels of water intake during labour.
Dr Moen said: "In labours exceeding eight to ten hours, a fluid intake of 300 millilitres per hour was sufficient for the development of hyponatremia."
Moen, V. et al. Hyponatremia complicating labour – rare or unrecognised? A prospective observational study. BJOG: An International Journal of Obstetrics and Gynaecology, Vol. 116, 2009, pp. 564-73.
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