An Exploration of Risk Factors for Severe Postpartum Haemorrhage in “Normal” Vaginal Births at Two Melbourne Hospitals 2013-2022

Blood loss of 1500 mLor more following birth, or severe postpartum haemorrhage (PPH), requires emergency treatment to minimise / stop further bleeding and prevent ongoing morbidity or, predominantly in low-middle income countries, mortality. The “4-Ts” are considered when assessing an individual’s likelihood of having a severe PPH and how to manage it should it occur. These include Thrombin: primary coagulation defects; Tone: how well the uterus contracts during 3rd stage; Tissue: ensuring that the placenta and membranes are completely delivered; and Trauma, including severe perineal trauma (3rd/4th degree), cervical or vaginal wall tears. These and other risk factors have been examined for women giving birth in Victoria 2009-2013a: the changing migration patterns may have altered the demographics and characteristics of the birthing population over the ensuing decade. To consider the risk factors that impact on EBL≥1500 mL following a “normal” (non-instrumental) vaginal birth with cephalic presentation at two maternity services in Victoria, operating under the same governance. Routinely collected data from 2013 to 2022 were downloaded for Hospital A, a tertiary, level 6 maternity service (~5600 births/year) and Hospital B, a level 4/5 service with ~3800 births/year. Statistical modelling explored risk factors for primiparous and multiparous women separately for each hospital. Variables with clinical and statistical significance on univariate analysis were analysed by stepwise backward multivariate regression to generate their adjusted odds ratios (aOR) and their 95% confidence intervals (CI). Women having their first baby were more likely than those having a subsequent baby to experience a PPH of ≥1500mL at both Hospital A (2.8% vs 1.6%) and Hospital B (3% vs 1.5%). Factors that increased this risk for both primipara and multipara at each hospital included maternal region of birth being Northern, Eastern or South-east Asia compared to those born in Australia, manual removal of the placenta and birthweight ≥4000 g. However, at Hospital B there was an increased risk of PPH in those born in Oceania (other than Australia), with aOR 2.2 (95%CI 1.2 to 3.9, p=0.01) and aOR 2.3 (95%CI 1.4 to 3.7, p<0.001) for multipara. Although the use of an oxytocin infusion in primipara increased the odds of PPH in both hospitals, an increased risk was only noted for multipara at Hospital A (aOR 1.9, 95%CI 1.4 to 2.4, p<0.001). A similar pattern was noted for severe genital tract trauma, with this not being seen to contribute to the risk of PPH in multiparous women at Hospital B. The contribution of known risk factors to severe PPH provide the opportunity to consider how to focus attention on prevention, such as ensuring judicious use of oxytocin infusions to induce or augment labour in primipara. Some factors are not modifiable and may require increased awareness of the potential for severe EBL and preparedness to anticipate and minimise it. For example, an understanding that women from specific regions such as Ocenia are at higher risk than their Australian-born counterparts at Hospital B may lead to working alongside these women and minimise their exposure to modifiable risk factors, such as high birthweight or severe genital tract trauma.