Increasing maternal age, obesity and Caesarean section rates could be reasons why maternal mortality is no longer falling in the UK

New research from Scotland published in Anaesthesia (a journal of the Association of Anaesthetists) shows the increased risk of severe maternal sickness/complications (morbidity) is associated with a range of risk factors including increasing maternal age and levels of obesity, and also previous Caesarean section.

The study, by Dr Nazir Lone, University of Edinburgh, Edinburgh, Scotland, UK and colleagues, suggests the increasing prevalence of all these risk factors could have combined to stall decades of progress in reducing maternal mortality in the UK. However, even though maternal mortality is no longer reducing (although the UK rate is low by international standards), nor is it going up – and the authors believe a possible explanation for this is that UK maternity services are continually adapting to meet the needs of this increasingly complex pregnant population.

The number of women dying during pregnancy and childbirth in the UK is at an all-time low¹. Consequently, enquiries into maternal death have limited power to improve maternal care, whereas measures of severe – but usually non-lethal – events during pregnancy and the puerperium (the period of about six weeks after childbirth during which the mother's reproductive organs return to their original non-pregnant condition) – may continue to inform care in the UK. A composite of various individual indicators of maternal ill health (or morbidity) is up to 100 times more frequent than maternal death, and thus interventions that can impact these indicators would provide opportunities to intervene to reduce both morbidity and mortality.

In this study, the authors analysed 17 diagnoses² and 9 interventions³ (including critical care admission) as a composite measure of severe maternal morbidity for pregnancies recorded over 14 years in Scotland. Any woman presenting with any of these conditions or needing any of these interventions was considered seriously ill.  

There were 762,918 pregnancies, of which 7947 (10 in 1000 pregnancies) recorded

9345 severe maternal morbidity events, with 2802 episodes of puerperal (post-natal) sepsis being the most common (30%). Severe maternal morbidity incidence almost doubled from 9 in 1000 pregnancies in 2012 to 17 in 1000 pregnancies in 2018, due in part to puerperal sepsis recording.⁴

The risk of severe maternal morbidity was higher for older women, with those aged 40 years and over 44% more likely and those 35-39 years 22% more likely that those aged 25-29 years to experience it. Women with severe obesity (BMI of 40 kg/m² or higher) were 32% more likely to experience severe maternal morbidity than those women in the normal weight range (BMI 18.5-24.9), while women in the less severely obese range (BMI 30-40) were 13% more likely than women of normal weight to experience it.

Women having a multiple pregnancy were 2.4 times more likely than women carrying a single baby to have severe maternal morbidity, and those with three or more pre-existing health problems were 4 times more likely to have it than women with no health problems. Women who had required a previous Caesarean delivery were 52% more likely to have severe maternal morbidity than those who had not.

The authors say: “The increasing prevalence of these factors in UK mothers might stall historical reductions in maternal mortality and will increase the need for healthcare during pregnancy and childbirth.”  They explain that one quarter (26%) of pregnant women had obesity (BMI>30) at the time of antenatal booking in 2021, while over half of pregnant women in Scotland had overweight or obesity (BMI >25) at the time of booking in 2021. The proportion of pregnant women with obesity has increased from 1 in 5 (20%) in 2011 to 1 in 4 (26%) in 2021.⁵

Women with severe maternal morbidity experienced greater adverse events than those without, including longer hospital stays following delivery (11% versus 3%), a greater frequency of stillbirths (1.7% versus 0.4%) and higher maternal death rates (365/100 000 pregnancies vs 1.6/100 000). Across all the pregnant women combined, the mortality rate was 5.4 per 100,000 pregnancies (this figure is lower than the 9.7 per 100,000 recorded in UK’s national figures [see link below] but as the data are recorded differently the two numbers are not directly comparable).

The authors conclude that: “Severe maternal morbidity accompanied 10 in 1000 (1%) pregnancies in Scotland. Morbidity was independently associated with maternal age; BMI; pre-existing health problems; previous smoking; previous caesarean section; multiple pregnancy; and mothers born in Africa, Asia or the Middle East. Morbidity was associated with delayed hospital discharge, stillbirths and maternal deaths.”

The identified risk factors are increasing in frequency and the authors note that those that are modifiable, such as obesity, require public health interventions on a population level, and are unlikely to change quickly. The situation around previous C-sections is complex as it includes some needed medically to reduce risk to the mother and baby due to older maternal age, increasing levels of obesity and pre-existing health problems.

They add that: “The reality today is that the increasing complexity of health care needs of women during pregnancy means that they may need greater levels of care during pregnancy and delivery. The fact that maternal mortality has stalled, rather than increased, suggests maternity services are adapting to these many challenges. However, our study may allow us to develop better systems to identify women at risk of severe maternal morbidity, so that maternity services can provide more personalised care targeted to those at higher risk.”

Dr Nazir Lone, Usher Institute, University of Edinburgh, Scotland, UK. Contact via University of Edinburgh Press Office. T) +44 (0)131 650 9547 E) press.office@ed.ac.uk

Alternative contact: Tony Kirby of Tony Kirby PR T) +44 7834 385827 E) tony@tonykirby.com

Notes to editors

1:  https://www.npeu.ox.ac.uk/assets/downloads/mbrrace-uk/reports/maternal-report-2020/MBRRACE-UK_Maternal_Report_Dec_2020_v10_ONLINE_VERSION_1404.pdf

2: The 17 diagnoses:

1. Acute Abdominal pain
2. Acute Renal Failure
3. Acute Psychosis
4. Cardiac Arrest/ Failure or Infarction
5. Cerebral Oedema or Coma
6. Disseminated Intravascular Coagulopathy
7. Cerebrovascular Accident
8. Major Complications of Anaesthesia
9. Obstetric Embolism (including Amniotic Fluid Embolism)
10. Shock
11. Sickle Cell Anaemia with Crisis
12. Status Asthmaticus
13. Status Epilepticus
14. Uterine Rupture
15. Eclampsia
16. Sepsis
17. Cerebral Venous Thrombosis

3: The 9 interventions:

1. Assisted Ventilation including Tracheostomy/ Admission to an Intensive Care Unit
2. Curettage in Combination with General Anaesthetic
3. Dialysis
4. Evacuation of Haematoma
5. Hysterectomy
6. Procedures to Reduce Blood Flow to Uterus
7. Re-closure of Disrupted Caesarean Section Wound
8. Repair of Bladder or Cystotomy
9. Repair of Intestine

4: The authors explain: “sepsis” is being more frequently recorded in health records, partly through better recognition, but also, it is likely that the term is being recorded too frequently, and therefore overestimating severe maternal morbidity. A strict definition of sepsis needs both the presence of infection, as well as an “over-reaction” from the body in response to the infection, leading to damage to vital organs, ultimately causing them to fail. Many of the recorded cases of sepsis are likely to only have the presence of infection, rather than the organ failure criterion. For this reason, in the discussion we suggest more accurate identification of sepsis might be achievable through combining coding for puerperal sepsis with data from other databases relating to organ failure, or admission to critical care, the latter likely to be marker for organ failure.

5: https://www.publichealthscotland.scot/publications/births-in-scottish-hospitals/births-in-scottish-hospitals-year-ending-31-march-2021/