Progesterone is thought to inhibit the production of proinflammatory cytokines and prostaglandins within the uterus and to inhibit myometrial contractility. Although a meta-analysis by Kierse et al. in 1990 suggested that progesterone may be beneficial in reducing the risk of preterm delivery, it was not until the publication of two trials in 2003 that there was more widespread interest in the possibility that progesterone may be used as a prophylactic treatment in women at high risk of preterm delivery. In 2003, Da Fonseca et al. reported that women who were at high risk of preterm delivery and were randomized to receive a 100-mg vaginal suppository daily between 24 and 33 weeks had a lower rate of preterm delivery (13.8% at 37 weeks, 2.8% before 34 weeks) versus the placebo group (28% before 37 weeks, 18.6% before 34 weeks). In a similar study Mies et al. used weekly injections of 17 a hydroxyprogesterone capruate (250 mg) between 16 and 36 weeks which reduced the preterm delivery rate from 55 to 36% before 37 weeks and 19 to 11% before 32 weeks. In this study the neonates of mothers treated with progesterone also had lower rates of necro-tizing enterocolitis, intraventricular haemorrhage and the need for supplemental oxygen. There are now a number of randomized controlled trials being conducted in various countries and, ideally, patients at high risk of preterm labour should be enrolled in one of these studies. However, the weight of both basic science and clinical evidence currently points towards progesterone being potentially beneficial in women at high risk of preterm delivery and there appear to be few, if any side effects.
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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.