Table S1.Definitions Condition Definition Anaemia Haemoglobin(Hb)<11 g/l,<10.5 g/l,<10 g/l antenatally, according todefinition. Antenatalday unit (ADU) Assessment unit forpregnant womenattending withunplanned concerns suchas APH and diminished fetalmovements as wellas for outpatient monitoring of hypertension,itching etc. Antepartum haemorrhage (APH) Bleeding from thebirth canalafterthe 24th week ofpregnancy. Birthweight (Kg) Maximum birthweight = largest infant;Totalbirth weight = additive weight ofallfetuses. Chorioamnionitis Inflammation of theamnionand chorioncaused by bacterial infection.Diagnosis defined byattending clinicians. Digit avoidance Numbers avoided,usuallyduetodocumentation of these volumes requiring action,leading tolower numbers selected (e.g.495 or 499 ml). Digit preference Numbers preferred and thereforevolumes rounded up ordowntoaccommodatethis preference (numbers ending in0 or 5,50 or 100 ml). Elective Caesareansection Planned surgicaldelivery,timed tosuit mother and/orstaff. EmergencyCaesarean section Surgical deliveryperformed due tofetaland/or maternalcompromise, whichmaybelife threatening. Estimated blood loss (EBL) Anestimate of thebloodvolume lost, usually achieved byvisualassessment,but also by weighing (especially fortheatre cases). Ethnicity As describedinNHSnotes. Generally unwell(no diagnosis) Attendanceat antenatal dayunit (ADU)with symptoms of lethargy, aches/discomfort,loss of appetite,not feeling “quite right”.No diagnosis madeortreatment given,as allinvestigations showed nodeviation from normal. Gestationalhypertension Blood pressure >140/90 on2 occasions at least 4 hours apart without proteinuria, diagnosedafter 20 weeks ofgestation. Femalegenitalmutilation (FGM) Alsoreferred toas femalecircumcision. Indexofmultiple deprivation (IMD) Thelevel ofsocialdeprivation, estimated by matching individualpostcodes toa small area (LocalSuper Output Area,LSOA) of~2,000 people,thentothe 2010 IMD forthat LSOA. Macrosomia Birthweight > 4.0kg,and >4.5kg Medications pre-birth Allmedications in week priorto birth, excluding labour. Nolabouronset Nolabouronset (spontaneous orinduced). This maybe followed byelectiveCaesarean sectionor anemergencyCaesareansectionfor concerns about maternal orfetalcondition. Physiologicalthird stage (orexpectant management) Following birthofthe baby,nouterotonic drug is given,no fundal guarding orcontrolled cord traction. The placenta and membranes areleft to separateandare delivered bymaternal effort. Placenta praevia Theplacenta is attached tothelower uterinewall(Major, minor,anterior and posterior) extendingto orcovering the internalcervicalos. Minor;reaches theloweruterinesegment and partially covers theos.Major;completely within the lower uterinesegment and theinternalos is occluded.Anterior;attached to theanterior uterine wall (minor ormajor).Posterior;attached totheposterior uterinewall(majororminor). Postpartum haemorrhage (PPH) • MinorPPH • Moderate PPH • SeverePPH Blood loss from thegenitaltract within24 hours of the birth ofa baby>500ml(WHO,1996) • EBL 500-999ml • EBL 1000-1499ml • EBL >1500ml,encompassing other thresholds usedpreviouslyinseverePPH i.e.>2000mland>2500ml, sometimes referred toas ‘major’,‘lifethreatening’, ‘massive’ or‘catastrophic’. Other definitions sometimes includeresponses suchas shockand blood transfusion. Pre-eclampsia Newonset hypertensionafter20thweekof pregnancyand significant proteinuria. Pre-eclampsia screen Suspicionofpre-eclampsia.SerialBP,urinalysis and blood takenforfullblood count,liver function tests,and renalfunction. Preterm prelabourrupture ofthe membranes Breaking of theamniotic sac beforelabourand before37 completed weeks ofgestation ProbablePPH Women with a fallinhaemoglobinof >4 g/l betweenlate pregnancy (>34 weeks)and postnatal,orwhereclinicians undertookactions indicativeofPPH suchas rubbing up a contraction, additionaluterotonics,insertion ofsecond cannula, use ofhead-downtilt etc. Raised temperature Temperatureriseabove 37.0 C, with normaland low temperatures treated as 0 C rise. Rupture of membranes (ROM) • Spontaneous • Artificial Breaking of theamniotic sac andexpulsionof the amniotic fluid. Mayoccurspontaneouslybeforeor during labouror artificiallyduring inductionor augmentationof labour. Spontaneous vaginal birth (SVD) Anormalvaginal birth,without the assistanceofa vacuum extractor orforceps. Steroids • Maternal • Fetal Maternalsteroids – prescribed formaternal reasons.Fetal steroids –administered IM tothe mother topromotefetal lung maturity. Threshold • Avoidance • Preference Thresholds inblood loss management aretypically 500ml, 1000ml,1500ml, 2000ml and 2500ml. Avoidance;use ofEBLs closetobut not at the recognised thresholds,usuallylower. Preference;use ofEBLs at therecognised thresholds. Urinarytract infection (UTI) Diagnosis of UTI documented inthe notes. ‘Warning’ APH (for PPH) 1)Recurrent (at least 3 episodes);2)Likea period orheavier;3)Placental.