Around half of pregnant women in the second and third trimester complain of leg cramps particularly at night. Plausible mechanisms involve deficiencies caused by the growing fetus: low potassium, calcium and magnesium (Mg) levels in addition to an increased Mg excretion via the kidney with the progression of pregnancy.

By far the strongest evidence involving pregnancy related cramps is pointing towards the link with Mg deficiency. Indeed, the prevalence of Mg deficiency in pregnant women varies between 16 to 20 %.

Magnesium (Mg) is the fourth most abundant essential mineral in the body. It is involved in the activity of more than 300 different enzymes. It also plays a crucial role in metabolism, hormonal reactions and muscle contraction.

More than 50% of the Mg in the body is distributed between muscles and soft tissues like skin. The other 50% of Mg is stored in the bones and very small amount is actually found in blood. For this reason, Mg deficiency can be difficult to diagnose with a blood test. The test result will not reflect the actual of what levels are in the tissues.

In skeletal muscle, Mg plays a role in relaxation. So when there is a deficiency the muscle will not be able to relax causing a muscle cramp.

Cramps are an involuntary, sudden, uncomfortable squeezing or contraction of a skeletal muscle. The two most places of predilection for pregnancy cramping to occur are the calves and the inner thighs known as the adductor muscles. In addition, to Mg deficiency, inner thigh cramps are most likely due to the muscle fatigue from carrying around the extra weight around the pelvis during pregnancy.

Magnesium substitution with adequate diet is recommended, however adherence to a Mg rich diet may not always be maintained. Thus the need for oral supplementation with Mg.

In fact, studies done on pregnant women suffering from leg cramps have shown that Mg supplementation with a particular formulation called Magnesium bisglycinate, improves the frequency and intensity of pregnancy-induced leg cramps. Therefore, oral magnesium may be a treatment option for women suffering from pregnancy-induced leg cramps