Outcomes for births booked under an independent midwife and births in NHS maternity units: matched comparison study

Strengths of study

This is the largest study to examine clinical outcomes over a period of years for women using an independent midwife. The IMA database covers most births in which an independent midwife is involved. We were able to match NHS births using anonymised NHS records on four variables, pre-empting the criticism that outcomes cannot be compared because women who employ an independent midwife are atypical. This relates in particular to socioeconomic status. In addition, our analysis adjusted for non-matched confounders such as previous medical and obstetric history.

Limitations

This was a retrospective study and subject to the usual constraints. Although the IMA believed the database sent to the research team to be nearly complete for all participating midwives, about 20% of independent midwives do not belong to the IMA and not all IMA members participated in the database project. Compared with more experienced independent midwives, some who were new to independent practice and who were starting to build up their caseload also did not participate.28 The IMA believe that data concerning over 70% of births involving independent midwife care were included in the database. Within a small group, where experiences are shared, the IMA thought it unlikely that a death would be not be reported.

While the IMA dataset had few missing variables, the ISD dataset was incomplete for certain variables, including analgesia, perineal tears, and breast feeding, and this compromised the power of the analysis for these outcomes. The data were complete for the primary outcome. As noted above, we also wanted to compare blood loss, augmentation of labour, and third stage management, but these data were not available from the ISD dataset.

Different models of care (for example, affecting continuity rates) might help to explain different outcomes, but we were not able to establish these for women in different units within the NHS—for example, “alongside midwife led unit,” “stand alone midwife led unit,” and obstetric unit.

Matching by deprivation fifths relies on postcode analysis, which does not measure individual socioeconomic status. Differences within the UK might also apply—for example, it is possible that someone in the fourth of the five categories of deprivation in Scotland is even more disadvantaged than someone in the same category in England (ISD, personal communication).

Perceptions of risk might simply be different for women who opt for certain choices.31 Given the lack of an objective and widely accepted tool for scoring obstetric risk, it would be extremely problematic to incorporate this factor when matching two cohorts.

We were not able to assess outcomes by ethnicity, as these data were not available from ISD. Scotland is less ethnically diverse than many other parts of the UK, the white population accounting for 98%. Of all the IMA mothers, 94% were classified as white.

Normality of birth

Our results are mixed. IMA cohort mothers were significantly more likely to have an unassisted vaginal birth (having started labour spontaneously) and to avoid pharmacological analgesia, including Entonox (nitrous oxide and oxygen). They were also more likely to avoid perineal trauma and to breast feed successfully. The 54.3% rate of unassisted vertex delivery for the NHS cohort is considerably lower than the average Scottish rate of 63.4%,32 suggesting that the mothers in this study are not representative of all mothers. Indeed, this was the point of carrying out a matched control study.

The mean gestational age at birth was almost identical in the two groups (despite the rates of prematurity and induction of labour being significantly higher in the NHS group), and there were no significant differences in Apgar scores. Admission to neonatal intensive care (another measure of neonatal morbidity) was far lower in the IMA group. This might be partly explained by the location of birth: babies born in hospital will be subject to unit protocols, some of which, for example, might require admission to intensive care for hypoglycaemia. Independent midwives at home births would not be obliged to follow NHS unit protocols. The cost of the number of preterm births and the apparently high number of NHS admissions in economic terms alone might be significant; this warrants further investigation.

Some of the outcomes might be linked. Induction of labour and certain forms of analgesia, for example, are associated with a higher incidence of instrumental or operative delivery.33 The average length of labour was significantly longer in the IMA cohort, which might be accounted for by different philosophies of intervention. Data on augmentation were not available for the NHS cohort, and national data are not published. The augmentation rate for IMA mothers, at 3.1%, however, seems to be low and certainly lower than the 19.7% cited in an Australian study.34

Breast feeding is the preferred method of infant feeding, and its promotion is a key government target.35 36 Breastfeeding rates at birth in the UK have increased in the past few years from 69% to 76%.37 It is recognised, however, that breast feeding declines after hospital discharge, and the latest government figures give the six week rate as 49%.35 At discharge, the NHS group in this study had a breastfeeding rate of 64%; the rate in the IMA group was significantly higher, even six weeks later, at 88%.

Perinatal mortality

Our overall findings show that women using an independent midwife fared better across a range of clinical outcomes. However, their babies were more likely to be stillborn or to die in the neonatal period. The stillbirth rate (singletons and twins) in the IMA cohort was twice that in the NHS cohort (1.0% v 0.5%). The rate for England, Wales, and Northern Ireland in 2005 was reported to be 0.55%38 and in Scotland it was 0.53%.39 While the unadjusted odds ratio among singletons was not significantly greater, the difference was significant when we included neonatal death.

Factors influencing mortality rates

Several factors could explain the higher perinatal mortality rate in the IMA cohort. Statistical artefact is a possibility: the incidence of perinatal deaths in the IMA database for 2006-8 is reported to be 10 (personal communication). After careful checking, we found only one death between 7 and 28 days in the NHS cohort (in addition to the 45 that occurred at birth or up to day seven); given the intense scrutiny surrounding perinatal deaths, under-reporting in the ISD cohort is unlikely. However, the analysis is based on small numbers, and resulting large confidence intervals.

In several cases multiple factors were involved (such as twin pregnancy and vaginal breech birth). Of the 25 perinatal deaths in the IMA cohort in 2002-5, seven babies (28%) were born at gestational ages ranging from 25-32 weeks. An even greater proportion of the babies who died in the NHS cohort, however, were born at or below 32 weeks (15/45; 33%). Only limited data were available about circumstances regarding transfer to hospital in the IMA cohort. While independent midwives’ observations of the reception by hospital staff on transfer were mostly positive, these also included “indifferent,” “unsupportive,” and “hostile.” It is possible that the anticipation of such a welcome might delay prompt transfer.40

Seven of the 25 IMA perinatal deaths occurred to a twin, of which three were vaginal breech births; there were three further vaginal breech births. As noted above, the IMA cohort mothers had a higher incidence of existing medical conditions and previous obstetric complications. Of those whose babies did not survive, one mother had an existing renal condition; another already had a child with cerebral palsy; and two had had a previous caesarean section. One of these, and another mother with a twin pregnancy and breech presentation, planned to have their babies in hospital (and did so).

Most of the IMA cohort births occurred at home, which some consider a risk factor in itself, although home birth studies in low risk women have found that their outcomes are no worse than for low risk women in hospital.10 18 All but one of the very preterm births noted in table 6 occurred in hospital. Indeed, most of the stillbirths in the IMA cohort (10/14) occurred in hospital. In eight of the 14 cases the fetal death had occurred before labour. While clinical mismanagement cannot be ruled out, it seems likely that other factors might be implicated. Five of the seven second twins in the IMA cohort who died were presenting by the breech.

When we excluded “high risk” cases (regardless of survival) from the entire IMA dataset, the perinatal mortality rate, at 4.8/1000, is comparable with the national rate. The conclusion might therefore be drawn that it is the additional “high risk” cases (such as preterm birth, twin pregnancy, and attempted vaginal breech birth, especially when combined) that account for the overall higher perinatal mortality rate. We cannot say with certainty that pregnant women who currently employ an independent midwife would use NHS services if the independent midwife option were not available. Some might choose to give birth without any assistance—known as “freebirthing”41—raising the possibility of even worse clinical outcomes.42

The IMA dataset contained information unavailable from the ISD. All of the IMA perinatal deaths occurred in cases where the mother was classified as white, so minority ethnic group status is clearly not an explanatory factor. In two of the perinatal deaths, the independent midwife noted life threatening birth defects (both were in twin pregnancies); in another, serious defects were reported pending postmortem examination. It is not known to what extent similar explanations might apply to the NHS cohort.

Twenty nine (3.3%) of the IMA cohort mothers had conceived by assisted means (in vitro fertilisation, intracytoplasmic sperm injection, etc). This is considerably higher than the national average, which is around one in 80 babies (1.4%).43 None of the babies in this category in the IMA cohort, however, was stillborn or died in the neonatal period. The IMA database also informed us that 19 mothers were considered to have had poor nutritional status; a further 250 (17.1%) had either a vegan, ovolacto-vegetarian, or macrobiotic diet. None of these factors was associated with perinatal death. No such data were available for the NHS cohort.

Thirty eight (2.6%) women in the IMA cohort reported having smoked during the pregnancy. Two of these experienced a perinatal death (one had smoked 30 cigarettes a day while pregnant). A further 534 (37%) stated they had drunk alcohol while pregnant, although none admitted drinking more than six units a week. In six cases the baby was either stillborn or died in the neonatal period. No comparable data were available for the NHS cohort, nor are national figures obtainable. Government advice, published in 2006, was not to drink more than one or two units of alcohol once or twice a week.44 This has been revised to a position of advising complete abstinence.45

Future research

We considered various potential explanations for the higher perinatal death rate in the IMA cohort and identified possible predisposing reasons, including twin pregnancy and breech presentation. These factors usually preclude eligibility for home birth under NHS clinical protocols.

Identifying precisely what occurred in the instances described here is a necessary next step. We were told that clients of independent midwives are more likely to decline aggressive treatments or interventions, which might have affected clinical outcome. In addition, two mothers chose to give birth at home, knowing there had been an intrauterine death (IMA, personal communication). We have secured funding for a senior academic to review the case notes to identify the factors that might have contributed to the higher perinatal mortality rate. All the perinatal deaths recounted in this study would have been reported to the Confidential Enquiry into Maternal and Child Health. Their reports covering stillbirth and neonatal death since 2000 have examined home births in detail and have not identified independent midwifery as a risk factor.38 46 47 48 In the event of a perinatal death, an independent midwife would also be obliged to report this to her or his supervisor of midwives, who would scrutinise practice.

The significantly higher incidence of preterm birth and low birth weight in the NHS group are matters of concern. There is some evidence that targeted antenatal care is associated with a lower incidence of preterm birth, even in high risk populations49; the effectiveness of different models of care requires further research. This was a UK study, and while the theme of home birth might be applied in other contexts, the circumstances of independent midwifery in the UK at present make extrapolations difficult. As Bastian et al note, home and hospital birth do not have standard care characteristics.8

Conclusion

Women are being advised that they can exercise choice in determining patterns of care. While the decision to opt for non-NHS care or home birth, or both, in the presence of identifiable risk factors might be difficult for some practitioners to accept, women’s perspectives on risk and safety in birth do not always accord with biomedical viewpoints.50 There is, in addition, clear legal justification for a mentally competent woman to choose an option that seems irrational or wrong to clinicians, even if the consequences are potentially fatal.51 Better communication regarding care options, which might include reviewing previous experiences or offering counselling or debriefing, might provide women with greater confidence in the NHS.

Evidence based decisions can be made only if appropriate information is available. While clinical outcomes across a range of variables are much better for women using an independent midwife, the significantly higher perinatal mortality rate, particularly in higher risk women, indicates the need for a full review of case notes to identify possible causative factors. Adequate plans need to be in place to manage clinical emergencies and to expedite transfer to a suitable facility when serious problems arise. A full review of these cases could help to explain the higher perinatal mortality rate in higher risk women and thereby provide women with further evidence on which to base their decisions about pregnancy care and delivery.