Anaemia is a cause and consequence of PPH. A cohort study in Assam, India found that women with moderate or severe anaemia had a greatly increased risk of PPH. Women with moderate anaemia had a 50% increased risk, whereas those with severe anaemia had a ten-fold increased risk of PPH. Anaemic women may be more susceptible to uterine atony due to impaired oxygen transport to the uterus. Anaemic women experience worse outcomes after PPH. An international survey of 275,000 women found that severe maternal outcomes after PPH were nearly three times more common in anaemic than in non-anaemic women. Even moderate bleeding can be life threatening in anaemic women. Excessive bleeding after childbirth worsens maternal anaemia, resulting in a vicious circle of bleeding and adverse outcomes. Fatigue due to anaemia severely limits a mothers' wellbeing and her ability to care for her children. Despite efforts to prevent anaemia, many women labour with perilously low haemoglobin levels

Tranexamic acid (TXA) inhibits fibrinolysis by blocking the lysine binding sites on plasminogen. TXA reduces surgical bleeding and death due to bleeding in trauma patients. The WOMAN trial assessed the effects of TXA in 20,060 women with PPH. When given within three hours of birth, TXA reduced death due to bleeding by nearly one-third (RR=0.69, 95% CI 0.52 to 0.91, p=0.008). However, for many women, treatment is too late to prevent death from PPH. Most PPH deaths occur in the first hours after giving birth and women with anaemia are at greatly increased risk. Whilst there have been some trials of TXA for the prevention of PPH, most have serious flaws and none collected data on maternal health and wellbeing. There is currently no reliable evidence about the effectiveness and safety of TXA for preventing PPH.

The WOMAN-2 trial will determine reliably the effects of TXA in anaemic women who give birth vaginally.

We will also conduct a pre-planned cohort analysis of data from the WOMAN-2 trial to assess the effect of pain control and episiotomy on the risk of post-partum haemorrhage. Adrenaline is a potent stimulus for fibrinolysis. Adrenaline causes the release of tissue plasminogen activator (TPA) from the endothelium. In trauma victims, high adrenaline levels are associated with increased fibrinolysis, decreased clot strength and increased deaths due to bleeding. Childbirth is intensely painful and maternal adrenaline levels are two to six times higher during labour. Maternal adrenaline concentrations peak in the second and third stages of labour but then rapidly return to normal after birth. Pain control can reduce the maternal catecholamine response. We hypothesize that painful procedures such as episiotomy will significantly increase the risk of postpartum haemorrhage and that pain control will reduce the risk of PPH.

The exposures of interest are the presence or absence of pain control during labour and delivery and whether episiotomy was conducted prior to birth. Pain control will be categorised as present or absent but the type of pain control administered during labour will also be described and examined. The types of pain control recorded in the study are epidural, opioids, 'other', or a combination of opioids and other pain control. For the multivariable regression analysis, the pain control variable was converted into a binary variable indicating whether a participant received any pain control or not. Episiotomy will be categorised as present or absent according to the CRF. The main outcome variable will be a clinical diagnosis of PPH (binary: yes/no), defined as an estimated blood loss of more than 500 mL or any blood loss sufficient to compromise haemodynamic stability within 24 hours. Potential confounding factors will include maternal age, BMI, anaemia, history of PPH, antepartum hemorrhage, hypertensive disease, multiple gestation, parity, prophylactic uterotonics, duration of labor, induction and augmentation of labor, assisted delivery, gestational age, birth canal trauma, placental abruption, and macrosomia.

We will use multivariable logistic regression to examine the association between pain control and episiotomy and the risk of PPH after adjusting for confounding factors. We will describe our causal assumptions using a directed acyclic graph. We will examine the association between the exposures of interest and PPH with odds ratios and 95% confidence intervals. We will estimate odds ratios and 95% CI for the crude association between the exposures of interest and PPH and after controlling for confounding factors. We will check for collinearity using variance inflation factors. Finally, we will examine whether the effect of pain control and episiotomy on the risk of PPH is modified by tranexamic acid treatment. To do this we will conduct stratified analysis and calculate a p-value for heterogeneity using a likelihood ratio test.