Methods
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1. Methods
The term, “maternal morbidity” encompasses a wide range of adverse medical conditions which may result in obstetric complications during pregnancy, labour and the puerperium. However, there is an absence of international consensus on definitions of “severe maternal morbidity”. To allow for international comparison, the NPEC adapted the validated methodology of the Scottish Confidential Audit of Severe Maternal Morbidity (SCASMM) to evaluate severe maternal morbidity (SMM) in Ireland. This methodology utilises organ dysfunction criteria described by Mantel et al6, with modifications used by SCASMM to include intervention-based criteria.7 Implemented nationally in 2011, this data collection tool, adapted for the Irish health care service, has been endorsed by the Clinical Advisory Group at the Institute of Obstetrics and Gynaecology and the HSE National Obstetric Programme Working Group.
2. Data collection and management
There are 19 maternity units in Ireland. Within each maternity unit data coordinators with the responsibility of submitting data on severe maternal morbidity events to the NPEC audit have been identified. Pseudonymised data on SMM events occurring between 1 January 2023 and 31 December 2024 were submitted to the NPEC using a standardised notification dataset electronically, via a secure online database, by 18 of the 19 maternity units. One tertiary referral maternity unit, the Rotunda Hospital, who had historically contributed to this SMM audit since its’ inception, did not submit data for the reporting years 2023 and 2024. In order to calculate national rates on maternal morbidities in Ireland, the NPEC has included published data from this unit’s clinical reports with SMM audit findings from the 18 contributing maternity units for the reporting years 2023/2024. Going forward it is hoped this unit will again be able to contribute to this national audit on SMM. The SMM notification dataset is available on the NPEC website.
The SMM dataset is completed based on data on maternal and fetal characteristics recorded in clinical records. Within NPEC the data are examined and, when necessary, reviewed with unit co-ordinators to ensure reported cases meet the specified audit criteria. In the event of in-utero or postpartum transfers between maternity units, potential duplicates in reporting are identified, thus ensuring data consistency and accuracy.
Figure III illustrates the NPEC data collection and management processes in the SMM audit. There has been a steady improvement in the overall quality of data reported by maternity units since the implementation of the NPEC SMM notification dataset in 2011. However, the timeliness of data submission remains a challenge in some maternity units. The lack of dedicated resources for clinical audit continues to impact negatively on timely collation of data at unit level.
3. Definitions and inclusion criteria for the SMM audit
In this audit, a severe maternal morbidity (SMM) event was defined as a pregnant or recently pregnant woman (i.e. up to 42 days following the pregnancy end) who experienced any of the following fourteen, clearly defined, organ dysfunction morbidities in the reporting years 2011-2024: major obstetric haemorrhage (MOH), uterine rupture, eclampsia, renal or liver dysfunction, pulmonary oedema, acute respiratory dysfunction, pulmonary embolism, cardiac arrest, coma, cerebrovascular event, status epilepticus, septicaemic shock, anaesthetic complications and maternities involving peripartum hysterectomy. To allow for direct comparison with the Scottish Confidential Audit Severe Maternal Morbidity (SCASMM), two management proxies for maternal morbidity - ICU/CCU admission and interventional radiology were also included.
Severe maternal morbidity events are included in a maternity unit’s SMM rate if the woman was delivered in the maternity unit or if the unit was the intended place of delivery, but the baby was born before arrival.
Maternal Morbidity Definitions
| Term | Definition |
|---|---|
| Major obstetric haemorrhage | Estimated blood loss ≥ 2500ml, or transfused 5 or more units of blood (Also includes ectopic pregnancy meeting these criteria) |
| Uterine rupture | A complete separation of the wall of the pregnant uterus, with or without expulsion of the fetus, involving rupture of membranes at the site of the uterine rupture or extension into uterine muscle separate from any previous scar, and endangering the life of the mother or fetus. Excluded: any asymptomatic palpable or visualised defect (e.g. dehiscence noted incidentally at caesarean delivery) |
| Peripartum hysterectomy | Peripartum hysterectomy |
| Eclampsia | Seizure associated with antepartum, intrapartum or postpartum symptoms and signs of pre-eclampsia |
| Renal or liver dysfunction | Acute onset of biochemical disturbance, urea >15mmol/l, creatinine>400mmol/l, AST/ALT >200u/l |
| Pulmonary oedema | Clinically diagnosed pulmonary oedema associated with acute breathlessness and O2 saturation <95%, requiring O2, diuretics or ventilation |
| Acute respiratory dysfunction | Requiring intubation or ventilation for >60 minutes (not including duration of general anaesthetic) |
| Pulmonary embolism | Increased respiratory rate (>20/min), tachycardia, hypotension. Diagnosed as “high” probability on V/Q scan or positive spiral chest CT scan. Treated by heparin, thrombolysis or embolectomy |
| Cardiac arrest | No detectable major pulse |
| Coma | Including diabetic coma. Unconscious for >12 hours |
| Cerebro-vascular event | Stroke, cerebral/cerebellar haemorrhage or infarction, subarachnoid haemorrhage, dural venous sinus thrombosis |
| Status epilepticus | Constant or near constant state of having seizures that last 30mins or more |
| Septicaemic shock | Sepsis induced tissue hypoperfusion or hypotension persisting after resuscitation with 30mls/kg intravenous isotonic crystalloid fluid as evidenced by: – Systolic blood pressure < 90 mmHg or MAP < 65 mmHg – Decrease in systolic blood pressure by 40mmHg from baseline and/or – Lactate > 4 mmol/l. |
| Anaesthetic problem | Aspiration, failed intubation, high spinal or epidural anaesthetic |
| ICU/CCU admission | Unit equipped to ventilate adults. Admission for one of the above problems or for any other reason. Includes CCU admissions |
| Other severe morbidity | Other severe morbidity, e.g. amniotic fluid embolism |
| Interventional radiology | Received planned (a) or unplanned (b) interventional radiology to prevent or arrest obstetric haemorrhage. (e.g Prophylactic Uterine Artery Embolisation, Arterial Balloon Occlusion, Balloon Cather Placement). |
4. Rate calculations
The SMM rate is a composite rate of a group of clearly defined severe morbidities. In keeping with the international published literature in this area, the incidence rate of SMM and of specific morbidities are calculated per 1,000 maternities resulting in the live birth or stillbirth. For incidence rates, 95% confidence intervals were calculated using exact Poisson confidence limits unless stated otherwise. Funnel plots are used to illustrate both the variation in incidence rates across participating maternity units and the deviation of ttehe rate for each individual unit from the national rate.
All denominator data used for this report were the number of maternities based on the number of women giving birth in Ireland, for the reporting years 2023 and 2024, to a livebirth or stillbirth with birth weight of ≥ 500g.
The denominator based on number of women who gave birth underestimates the number of women at risk of SMM as it does not include women experiencing miscarriage, ectopic pregnancy, termination of pregnancy (TOP) and molar pregnancy, which may be reported as cases of SMM and thereby are included in the numerator. However, complete data on maternities resulting in miscarriage, ectopic pregnancy, TOP and molar pregnancy are not available and so, to ensure uniformity, the denominator was restricted to women who gave birth to a live born or stillborn baby ≥ 500g . The approach of not including miscarriage, ectopic pregnancy, TOP and molar pregnancy in the denominator was also the approach taken by the SCASMM and confidential enquiries on maternal deaths in Ireland and the UK.7-9
The infrequency of some specific rarer SMMs compared to those more frequently recorded, such as major obstetric haemorrhage (MOH) and ICU/CCU admission, makes it difficult to assess time trends based on the annual rate. The fourteen-year period of the SMM audit is now long enough to allow these morbidities time trends to be examined by triennium. Hence, rates of renal dysfunction, peripartum hysterectomy, pulmonary embolism and septicaemic shock were calculated by triennium in this and recent reports.
5. Interpretating rate ratios and funnel plots
To access information on interpreting rate ratios and funnel plots, click here