NZ study finds more adverse outcomes in midwife deliveries

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midwifefocuswebMothers using midwives are more likely to have adverse outcomes for their newborns than those who use obstetricians, according to a retrospective study of nearly a quarter million babies born in New Zealand. The findings ‘are of concern’ in the context of NZ’s internationally comparable birth outcomes and a 2016 Cochrane systematic review that found no increase in adverse events with midwife care.

The study was by Ellie Wernham of University of Otago, New Zealand and colleagues.

In 1990, New Zealand adopted a midwife-led model of maternity care, giving midwives the ability to practice autonomously and be fully reimbursed by the government, offering patients free care. As a result, more than four out of five New Zealand mothers use midwives throughout pregnancy and delivery, with doctors generally only getting involved when there are risk factors.

Wernham and colleagues examined data on all 244,047 full-term births, with no major foetal or neonatal congenital, chromosomal, or metabolic abnormalities, that occurred in New Zealand over the five years spanning 2008 through 2012 and compared adverse outcomes for newborns born to mothers under midwife-led care to outcomes with doctor-led care at first registration.

The outcomes included oxygen deprivation during delivery, an infant’s size, stillbirths, mortality, and neonatal encephalopathy – a condition that can result in brain injury, as well as Apgar scores – a measure of infant well-being immediately after delivery.

Compared with the midwife-led model and after adjusting for demographics, socioeconomic factors, and pre-existing conditions, the researchers observed lower odds of some adverse birth outcomes when maternity care was managed medically, including 55% (95% confidence intervals [CI] 0.32–0.62) lower odds of birth related asphyxia, 39% (95% CI 0.38–0.97) lower odds of neonatal encephalopathy, and 48% (95% CI 0.43–0.64) lower odds of a low Apgar score at five minute after delivery. There were no significant differences between the midwife-led and doctor-led births for neonatal mortality and intrauterine hypoxia.

The study was limited by the lack of data on adverse events for mothers, its retrospective design, and that the demographics – while adjusted for – were different in the two groups.

The authors say: “Despite New Zealand having overall internationally comparable maternity outcomes, the findings of this study suggest that avoidable adverse outcomes may still be occurring.”

In an accompanying Perspective, Ank de Jonge at the department of midwifery science, AVAG/ EMGO Institute for Health and Care Research, VU University Medical Centre, Amsterdam and Jane Sandall, professor of social science and women’s health, department/division at Kings College London discuss the discrepancy between the new study and a 2016 Cochrane systematic review that found no increase in adverse events with midwife care. Differences in both how the study was conducted – such as how adverse events were detected – as well as how midwife care is organized in New Zealand compared to other countries are the most likely explanations, they say, adding that “multi-disciplinary research is required to understand mechanisms leading to differences in processes, outcomes, costs, and women’s experiences between midwife-led continuity of care and other models of care.”

Background: Internationally, a typical model of maternity care is a medically led system with varying levels of midwifery input. New Zealand has a midwife-led model of care, and there are movements in other countries to adopt such a system. There is a paucity of systemic evaluation that formally investigates safety-related outcomes in relationship to midwife-led care within an entire maternity service. The main objective of this study was to compare major adverse perinatal outcomes between midwife-led and medical-led maternity care in New Zealand.
Methods and Findings: This was a population-based retrospective cohort study. Participants were mother/baby pairs for all 244,047 singleton, term deliveries occurring between 1 January 2008 and 31 December 2012 in New Zealand in which no major fetal, neonatal, chromosomal or metabolic abnormality was identified and the mother was first registered with a midwife, obstetrician, or general practitioner as lead maternity carer. Main outcome measures were low Apgar score at five min, intrauterine hypoxia, birth-related asphyxia, neonatal encephalopathy, small for gestational age (as a negative control), and mortality outcomes (perinatal related mortality, stillbirth, and neonatal mortality). Logistic regression models were fitted, with crude and adjusted odds ratios (ORs) generated for each outcome for midwife-led versus medical-led care (based on lead maternity carer at first registration) with 95% confidence intervals. Fully adjusted models included age, ethnicity, deprivation, trimester of registration, parity, smoking, body mass index (BMI), and pre-existing diabetes and/or hypertension in the model. Of the 244,047 pregnancies included in the study, 223,385 (91.5%) were first registered with a midwife lead maternity carer, and 20,662 (8.5%) with a medical lead maternity carer. Adjusted ORs showed that medical-led births were associated with lower odds of an Apgar score of less than seven at 5 min (OR 0.52; 95% confidence interval 0.43–0.64), intrauterine hypoxia (OR 0.79; 0.62–1.02), birth-related asphyxia (OR 0.45; 0.32–0.62), and neonatal encephalopathy (OR 0.61; 0.38–0.97). No association was found between lead carer at first registration and being small for gestational age (SGA), which was included as a negative control (OR 1.00; 0.95–1.05). It was not possible to definitively determine whether one model of care was associated with fewer infant deaths, with ORs for the medical-led model compared with the midwife-led model being 0.80 (0.54–1.19) for perinatal related mortality, 0.86 (0.55–1.34) for stillbirth, and 0.62 (0.25–1.53) for neonatal mortality. Major limitations were related to the use of routine data in which some variables lacked detail; for example, we were unable to differentiate the midwife-led group into those who had received medical input during pregnancy and those who had not.
Conclusions: There is an unexplained excess of adverse events in midwife-led deliveries in New Zealand where midwives practice autonomously. The findings are of concern and demonstrate a need for further research that specifically investigates the reasons for the apparent excess of adverse outcomes in mothers with midwife-led care. These findings should be interpreted in the context of New Zealand’s internationally comparable birth outcomes and in the context of research that supports the many benefits of midwife-led care, such as greater patient satisfaction and lower intervention rates.

Ellie Wernham, Jason Gurney, James Stanley, Lis Ellison-Loschmann, Diana Sarfati

PLOS material
PLOS Medicine abstract
PLOS Medicine perspective

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