Prevention of Postpartum Haemorrhage

Published trials on tranexamic acid (TxA) for prevention have used a variety of fixed (0.5gm or 1gm) and body-weight adjusted (10mg/kg or 15mg/kg) doses of TxA. Given the wide range of bodyweights of pregnant women in contemporary obstetric practice, it is critical to determine the minimum effective dose of TxA, so as to avoid under- or over-dosing. The rationale of this study is to determine the minimum effective dose of TxA that is required to attain therapeutic plasma levels of TxA, established at 5-15mg/L, following administration of a single dose of intravenous (IV) TxA after childbirth and the clamping the umbilical cord, and before delivery of the placenta. Following birth of the infant, and upon clamping the umbilical cord, the investigators will administer a single dose of IV TxA in 100ml of 0.9% sodium chloride at 50mg/min according to the dose-escalation schedule described below. The slow rate of infusion has been chosen to prevent untoward effects such as hypotension that have been noted when the rate of infusion has exceeded 100mg/min. As part of the dose-escalation design, the investigators will start with 5mg/kg, half the smallest described dose, on a sample of up to 5 women. They will continue to administer TxA doses in increments of 5mg/kg to each successive batch of 5 women. If the number of treatment successes cannot statistically rule out a value < 75% (< 4 of 5 women are successes due to values in the low range), the dose will be increased by 5mg/kg for the next set of 5 women, and so on, until a maximum dose of 30mg/kg is reached, a dose deemed safe based on earlier studies in different populations. Once treatment success is determined at a certain dose, i.e. 4/5 women have levels in the therapeutic range), a total of 20 women will be administered that dose to ensure that 75% i.e. 18/20 women are successes at that dose.