4.2 Interpretation
Our study found women were more likely to require an emergency caesarean section if they received ≥ 2500 mL IV fluids compared to <2500 mL. This finding is in contrast to Coco et al. (24) and Garite et al.(14) that reported no statistical difference for total caesarean sections in their randomised controlled trials (RCTs) evaluating increased rates of IV fluids to nulliparous women in spontaneous labour. Duffy et al.(13) also reported no statistical difference in caesarean section rates for their more recent RCT examining increased IV hydration in nulliparous women undergoing induction of labour. However, it is important to note that our study included both nulliparous and parous women, in either spontaneous, augmented, or induced labour, and had a much larger sample size than these three RCTs. Similarities included the IV fluid types and the overall total volume administered between intervention and controls, with both Coco et al.(24) and Garite et al.(14) reporting total IV fluids volumes of approximately 2500 mL or greater for their increased IV fluids group. In contrast, Duffy et al.(13) reported much larger mean IV fluids volumes of 3476.8 mL for their 125 mL/hr group and 6984.5 mL for their 250 mL/hr group. PPH was not a reported outcome of Duffy et al.(13)
Whilst our study was not designed to answer the specifics as to why this result may have occurred, it is conceivable that IV fluids in labour may influence the power, passenger, or passage. For example, through increased fetal weight from the transfer of additional IV fluids across the placenta.(25, 26) Additionally, there is biological plausibility that altered uterine contractility related to IV fluids administration could increase the risk of emergency caesarean section.(15) In the work by Moen et al.,(27) there was a statistically significant correlation between perinatal hyponatraemia (plasma sodium levels <130 mmol/L) and emergency caesarean section for slow progress in labour. Our results support the need for further prospective research, ideally larger sized RCTs examining the administration of IV fluids in labour and maternal outcomes such as emergency caesarean section for slow progress in labour.
Finally, our observed rates of PPH ≥ 500 mL and PPH ≥ 1000 mL of 33.1% and 8.6% of births respectively were higher than expected. In 2021, the rate of PPH within Australia was approximately 21%. (28) However, the true rate may be higher, with differences in definitions and reporting methods possibly contributing to underreporting.(6, 7) The rate of PPH in this study was comparable to a UK cohort examined by Briley et al. (7) who reported a 33.7% incidence for PPH ≥ 500 mL and 3.9% for PPH ≥ 1000 mL. The authors reported that to the best of their knowledge, it was the highest incidence of PPH reported from any high-income or low-income country and concluded that there is a need for policy and research to focus on potentially modifiable risk factors for PPH.(7) This sentiment is echoed by the World Health Organization and in Australia, with the prevention and management of primary PPH seen as an area of research priority due to the potential for maternal death and negative long-term health impacts for both mother and baby.(29, 30)