Muscle cramps, including leg cramps in pregnant women
Muscle cramps are common and usually do not have a serious cause. Cramps are simultaneous involuntary contractions of motor units that cause pain due to local lactic acidosis. In a few people, cramps are due to electrolyte abnormalities, especially hyponatraemia and hypocalcaemia. Cramps can also occur with metabolic conditions (eg thyroid disturbance) and neurological conditions (eg peripheral neuropathy, muscle disease, motor neurone disease).
Despite widespread use of magnesium supplements to treat idiopathic muscle cramps and cramps associated with disease or exercise, there is no evidence to support this. However, some people get symptomatic relief.
Quinine has been associated with a reduced cramp intensity and cramp frequency, but has also been rarely associated with serious adverse events, including thrombocytopaenia. It is no longer approved in Australia to treat idiopathic nocturnal cramps.
Leg cramps have been reported in up to 30% of pregnant women, and are most common in the second and third trimesters. These cramps usually affect the calves and occur at night in 75% of cases. The cause is unknown. A systematic review of treatment for muscle cramps in pregnancy evaluated oral magnesium, calcium, vitamin B and vitamin C1. The quality of the included studies was not sufficient to reach firm conclusions. However, it is common to try magnesium and calcium supplements. Performing stretching exercises before bed and maintaining adequate hydration can help.