Objective: To evaluate whether the administration of high-volume intravenous (IV) fluids during labour (≥ 2500 mL) increases the risk of primary postpartum haemorrhage (PPH) and other adverse outcomes for women with a term, singleton pregnancy, in comparison to low-volume IV fluids during labour (<2500 mL). Design: Retrospective cohort study Setting: Tertiary referral hospital in Sydney, Australia Sample: 1023 women with a live singleton fetus in a cephalic presentation; planning a vaginal birth; and admitted for labour and birth care between 37 - 42 weeks gestation. Methods: The study factor was IV fluids during labour. Birth and postnatal data were obtained from electronic medical records and paper fluid order documentation. Multivariable logistic regression and multiple imputation were used to explore the relationship between volume of IV fluids in labour and PPH. Main outcome measures: The primary outcome was primary PPH ≥ 500mL. Secondary outcomes included caesarean section and major perineal injury. Results: 1023 participants were included of which 339 had a primary PPH (33.1%). There was no association between high-volume IV fluids and PPH after adjusting for demographic and clinical factors (Adjusted odds ratio [OR adj]1.02 95% confidence interval [95%CI] 0.72, 1.44). However, there was a positive association between high-volume IV fluids and caesarean section (OR adj 1.99; 95%CI 1.4, 2.8). Conclusion: These findings are important to further knowledge relating to administration of IV fluids in labour and the potential impact of this common practice. It identifies future research priorities around documentation of IV fluids and their relationship with pregnancy and perinatal outcomes.

Title:Letter to Editor:Re: Impact of analysis technique on our understanding of the natural history of labour

Objective: Caesarean delivery rates continue to rise globally the reasons for which are poorly understood. We aimed to characterize attributable factors for increasing caesarean delivery rates over a 30-year period within our health network. Design: Observational cohort study. Setting: Two hospitals (large tertiary referral hospital and metropolitan hospital) in Sydney, Australia, across two time periods: 1989-1999 and 2009-2016, between which the caesarean delivery rate increased from 19% to 30%. Participants: All women who had a caesarean delivery after 24 weeks gestation Methods: Data were analysed using multiple imputation and robust Poisson regression to estimate the changes in the caesarean delivery rate attributable to maternal and clinical factors. Main outcome measures: Caesarean delivery. Results: Fifty-six percent of the increase in the rate of caesarean delivery was attributed to changes in the distribution of maternal factors including maternal age, body mass index, parity and history of previous caesarean delivery. When changes in the obstetric management of multiple gestation, malpresentation and preterm singleton birth were considered, 66% of the increase in caesarean rate was explained. When pre-labour caesarean deliveries for maternal choice, suspected fetal compromise, previous pregnancy issues and suspected large fetus were excluded, 78% of the increase was explained. Conclusions: Most of the steep rise in the caesarean delivery rate from 19% to 30% is attributable to changes in maternal demographic and clinical factors.

Mini-commentary on BJOG-20-1459.R1: Caesarean birth and risk of subsequent preterm birth: retrospective cohort studyDeclarative title to be addedBradley de VriesSchool of Public HealthUniversity of SydneySydneyNew South WalesAustraliaWorldwide, preterm birth occurs in 11% of pregnancies and is the leading cause of childhood mortality. Complications from preterm birth are the most common cause of neonatal death in the United Kingdom, yet the incidence of preterm birth is not falling.In this issue of BJOG, Williams et al (BJOG xxxx) report on an observational study which identifies previous second stage caesarean birth as a risk factor for spontaneous preterm birth, confirming the results of other observational cohorts. Among women with one previous term birth, the adjusted odds ratio was 2.1 (95% confidence interval [CI] 1.3 to 3.1) for preterm birth before 37 weeks gestational age and 7.5 (95% CI 3.4 to 15) for preterm birth before 34 weeks, for previous second stage caesarean birth compared with previous vaginal birth. They adjusted for confounders not addressed in other studies including interpregnancy interval and maternal deprivation index, strengthening the existing evidence. The association is plausible because the cervix and lower uterine segment are anatomically merged in the second stage of labour and inadvertent cervical incision might damage the integrity of the cervix. The association was at least as strong as that described for previous excisional surgery for cervical dysplasia. Current National Institute of Clinical Excellence Guidelines recommend considering prophylactic cervical cerclage for an ultrasound-measured cervical length < 25mm if there is a history of cervical trauma. Given the plausibility and emerging epidemiological evidence, it would seem prudent to offer the same screening and treatment when there is a history of second stage caesarean birth.The observed association is relevant in other ways. Counselling about instrumental versus caesarean birth may be influenced by knowledge of future risks. Additionally, surgeons may need to be aware of the potential importance of avoiding inadvertent cervical incision, while still avoiding upper segment incision and its attendant risk of future intrapartum uterine rupture.The study by Williams et al is well designed, yet there remains potential for confounding not adjusted for in the analysis. Further, missing data for body mass index (1.6%) and cigarette smoking (13%) were classified as unknown and not imputed which can also cause bias. As there are only a handful of observational studies, it would be sensible to confirm the association, and explore potential causative mechanisms (e.g., by monitoring cervical length in subsequent pregnancies).Clinical prediction models for spontaneous preterm labour in asymptomatic women have been developed but need improvement before incorporation into clinical practice. Addition of new risk factors such as second stage caesarean birth and better understanding of the causes of preterm birth could improve these models and ultimately improve outcomes through offering prophylaxis with cervical cerclage, vaginal progesterone, or pessary for women at high risk.Given the massive personal, clinical, and economic burden imposed by preterm birth, the plausibility of the association, and the growing evidence from observational studies, I believe cervical surveillance warranted, with a view to offering prophylactic measures when there is a history of second stage caesarean birth.No disclosures: A completed disclosure of interest form is available to view online as supporting information.