Relationship between uterine contractions and serum magnesium levels in patients treated for threatened preterm labour with intravenous magnesium sulphate.

We aimed to correlate the assessment of preterm uterine activity with serum magnesium levels in women with threatened preterm labour. The observational study involved twelve women receiving intravenous magnesium sulphate for threatened preterm labour. Mean gestational age at initiation of therapy was 26.9+/-2.9 weeks. Mean cervical dilatation at initiation of therapy was 1.5 cm. Serum magnesium levels and evaluation of uterine contractions by external tocograph were assessed twice daily. Presence or absence of contractions was analysed for correlation with plasma magnesium levels. Eighty-eight measurements were analysed. The mean serum magnesium levels were 1.9+/-0.5 mmol/l and 1.9+/-0.3 mmol/l in the presence (n=22) or absence (n=66) of contractions, respectively. The difference did not reach statistical significance. No correlation was found between serum magnesium levels and presence of contractions (P=0.3, logistic regression odds ratio 1.1, 95% confidence interval of 0.6-2.0). The abolition of premature uterine contractions during intravenous magnesium sulphate therapy does not correlate with serum magnesium levels.