Prior to the 1980s magnesium sulphate was widely used in the United States in the intrapartum management of pre-eclampsia and eclampsia and the clinical impression that magnesium sulphate made induction of labour more difficult led to its evaluation as a tocolytic agent. With the withdrawal of sympathomimetic drugs from the
American market and the failure of atosiban, an oxytocin antagonist, to obtain FDA approval, there are no licensed tocolytic drugs available for the American obstetrician to use and magnesium sulphate is therefore in common use (Fig. 21.6). However, randomized placebo-controlled trials of magnesium sulphate show no significant short-term delay of delivery, increase in birthweight or difference in perinatal mortality when compared to placebo. Studies where magnesium has been compared to sympathomimetics have suggested equal efficacy. These two apparently contradictory findings can probably be explained by the lack of power of the studies to detect a significance difference between drugs with little or no efficacy but a high placebo response rate.
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The first trimester is very important for the mother and the baby. For most women it is common to find out about their pregnancy after they have missed their menstrual cycle. Since, not all women note their menstrual cycle and dates of intercourse, it may cause slight confusion about the exact date of conception. That is why most women find out that they are pregnant only after one month of pregnancy.