An estimation of intrapartum-related perinatal mortality rates for booked home births in England and Wales between 1994 and 2003

Abstract

Objective  The objective of this study was to obtain the best estimate of intrapartum-related perinatal mortality (IPPM) rates for booked home births.

Design  A population-based cross-sectional study.

Setting  England and Wales.

Subjects  All births in England and Wales, including home births (intended or unintended) occurring between 1994 and 2003.

Methods  All IPPM data were derived from the Confidential Enquiry into Maternal and Child Health. Denominators were derived by using unintended home births and transfer rates from home to hospital, from previous studies, with sensitivity analyses. IPPM rates were calculated for the three following subgroups: (a) the completed home birth group, (b) the transferred group and (c) the unintended home birth group.

Outcome  IPPM rate.

Results  The overall IPPM rate for England and Wales improved between 1994 and 2003. However, data to obtain a precise estimate of IPPM rate for booked home birth were not available. The average IPPM rate for all births in the study period was 0.79 per 1000 births (95% CI 0.77–0.81), and the estimated IPPM rate for booked home births was 1.28 or 0.74 per 1000 births, depending on the method of calculation (range 0.49–1.47). The IPPM rates for the completed home birth group appeared to be lower throughout the study period compared with the unintended home birth groups. Those women who had booked for a home birth, but later needed to transfer their care for a hospital birth, appeared to have the highest risk of IPPM in the study period.

Conclusions  The results of this study need to be interpreted with caution due to inconsistencies occurring in the recorded data. However, the data do highlight two important features. First, they suggest that IPPM rates for home births do not appear to have improved over the study period examined, even though rates did so overall. Second, although the women who booked for home births and had their babies at home seemed to have a generally low IPPM rate, those who required their care to be transferred to hospital did not. Women who book for home births should be offered comprehensive evidence-based information about the potential benefits, risks and uncertainties associated with their choice of birthplace by the healthcare professional responsible for supporting their decision. It is of considerable concern that the data recorded nationally in England and Wales do not provide accurate information about when and why a transfer from home to hospital booking occurs and about their outcomes.

Introduction

The relative safety of a home birth versus a hospital birth has been debated for years, but uncertainty remains.¹ Most previous studies evaluated perinatal mortality rates as a marker for safety, but the results have been conflicting.^2–8 However, intrapartum-related perinatal mortality (IPPM) rate has been used in an attempt to reflect intrapartum events in relation to place of birth more precisely as it excludes deaths from other causes, such as prematurity, infection and structural abnormalities.⁹ Although it has been considered in two studies,^9,10 IPPM has not been an established measurement and hence is not often routinely collected.

Another difficulty in using existing data is that most home birth statistics include unintended home births and do not separately identify those who intended a home birth but transferred to hospital before birth.¹⁰

This paper reports analyses of routinely collected national data, ultimately aiming to achieve the best estimate of the IPPM rate for booked home births in England and Wales.

Method

Study design

Population-based cross-sectional data were analysed. The primary focus was on booked home births with the outcome established by comparing IPPM rates derived from the Confidential Enquiry into Maternal and Child Health (CEMACH: previously the Confidential Enquiry into Stillbirths and Deaths in Infancy [CESDI]), with overall national IPPM rates. Data about all women who gave birth at home either intentionally or unintentionally in England and Wales between 1994 and 2003 were included.

Definitions

Definitions of the terms used in this report are as follows:

IPPM rate

IPPM rate is defined as deaths from intrapartum ‘asphyxia’, ‘anoxia’ or ‘trauma’, derived from the extended Wigglesworth classification 3, which is used by CEMACH.^11,12 This includes stillbirths and death in the first week. The denominator was all births (live births and stillbirths).

Booked, unintended and actual home birth

Booked home birth refers to the intended place of birth at the time of the first antenatal visit (booking). This can include a woman who intended a home birth at booking, who may have later transferred her care during pregnancy or labour.

Unintended home birth refers to women who gave birth at home but at booking had actually intended to give birth elsewhere.

Actual home birth refers to all births (intended and unintended) that occurred at home. Completed home birth refers to women who intended to have a home birth at booking and gave birth at home.

Transferred birth refers to women who intended to have a home birth at booking but had babies in hospital or elsewhere.

Unintended home birth rate and transfer rate

The unintended home birth rate can be calculated in two ways. First, it was derived by simple subtraction of the unintended births from the total home births (calculation A). The Northern Region data (the best available) were used, and it was seen that the proportion of unintended home births among all the births occurring in the region was consistent through the years.¹³ Although calculation A is a standard method to obtain this rate, a different method (calculation B) was also used. In this calculation, the unintended rate was calculated from the unintended births as a percentage of the overall birth rate.

The transfer rate refers to the proportion of all women who intended a home birth at booking but who gave birth in hospital or elsewhere, against the total of women who intended a home birth at booking. The transfer includes those that occurred during pregnancy, as well as in labour.

Data collection

IPPM

The numbers for the overall IPPM and those for each subgroup of home births in England and Wales, between 1994 and 2003, were obtained from CEMACH who collect data for all deaths by intended place of birth at booking.

Unintended home birth and transfer rates

Unintended home births and transfer rates were extracted from previous studies identified through a systematic search of medical databases (Medline, EMBASE, BNI, CINAHL and MIDIRS) using keywords such as ‘home birth’ and reference lists of relevant articles. Inclusion criteria stipulated that studies were:

• 1
  Conducted in the UK.
• 2
  Population-based defined as a study that captures all or nearly all of women in a certain defined area.
• 3
  Using the same definition of unintended home birth and transfer as above. Details of the systematic reviews are available from the authors. These rates were used to obtain weighted means and to set ranges for sensitivity analysis to calculate denominators for the subgroups of home birth.

Details of this systematic review used to obtain unintended home birth and transfer rates are available in the electronic version of the paper.

Denominators (birth numbers) for all national births and actual home births

The numbers of all births and actual home births between 1994 and 2003 in England and Wales were obtained from the Office for National Statistics (ONS).^14,15

Calculation and statistical analysis

Denominators (birth numbers) for booked home birth and the subgroups

Calculation of booked home birth and the other home birth subgroups are outlined in Figure 1. The number of births from the ONS (step 1), which relates to the actual place of birth, has been modified by removing the unintended home births (step 2) and then adding back the likely transfers to provide an estimated number of women who had an intended home birth at booking (step 3).

Figure 1. Calculation of denominators for booked home birth group and other home birth subgroups.

IPPM rate of all births and actual home birth for England and Wales

IPPM rates were calculated from the data described above. Confidence intervals were calculated because each birth can be considered as a realisation from a hypothetical population. Chi-square tests were performed to test for trends when appropriate.

IPPM rates for the booked and the subgroups of home birth

IPPM rates for the booked home birth and the three subgroups of home birth were calculated by using the estimated denominators described above. Sensitivity analyses were performed using the lower and upper limits of values derived from previous studies using both calculations A and B. Risk ratios were not obtained due to uncertainty about the reliability of the estimation and confounding factors involved.

Trend of the IPPM rates for booked home birth and actual home birth over the study years

Trend of IPPM rates for booked home birth and actual home birth as well as the national average over the study years are examined.

Ethical considerations

As all the data are derived from open resources, research ethics committee approval was not considered necessary.

Results

Overall IPPM rate

A total of 4991 intrapartum perinatal deaths occurred in England and Wales between 1994 and 2003 among 6 314 315 births. The IPPM rates significantly improved over these years (test for trend: chi-square value = 100.92, df= 1, P < 0.001; Figure 2).

Figure 2. Trend of IPPM for national average, booked home birth (estimate) and actual home birth in England and Wales from 1994 to 2003.

IPPM rate for actual home births

There were 125 intrapartum-related deaths among the 130 700 home births in England and Wales in this period. The IPPM rate was 0.96 per 1000 births (95% CI 0.79–1.03).

Unintended home birth rates from previous studies

Unintended home birth rates were taken from previous studies conducted in England and Wales. (Table 1).

Table 1.  Unintended and transfer rates from previous studies conducted in England and Wales

Author	Conducted year	Unintended rate*	Transfer rate** (%)	Region
NRPMSCG, Northern Region Perinatal Mortality Survey Coordinating Group. * Proportion of women who did not book a home birth but had babies at home/all actual home births (A and B: calculations A and B). ** Proportion of women who booked home births but did not have babies at home/all home birth bookings. *** No denominator was obtained; hence, this was not included to calculate the weighted mean.
Murphy et al.^13	1970–79	34.1% A (0.36% B)		Cardiff
Ford et al.^16	1977–89	Not reported	18.8	London
Shearer^17	1978–83	Not reported	11.9	Essex
NRPMSCG^10	1983	56.0% A	35.0***	Northern Region
	1981–94	0.31% B		Northern Region
NRPMSCG^18	1988	47.0% A	Not reported	Northern Region
Davies et al.^8	1993	45.0% A	43.0	Northern Region
Chamberlain et al.^2	1994	Not reported	16.0	England and Wales
Redshaw et al.^19	2006	0.75% B		England
Weighted mean		50.7% A (0.32% B)	14.3
Sensitivity analysis	Lower	45.0% A (0.31% B)	11.9
	Upper	56.0% A (0.75% B)	43.0

The unintended home birth rates ranged from 45.0 to 56.0% for calculation A and from 0.31 to 0.75% for calculation B. The weighted mean of all the included studies was 50.7% for A and 0.32% for B. As a result, ranges for sensitivity analyses were set as 45.0–56.0% for calculation A and 0.31–0.75% for calculation B.

Transfer rates from previous studies

Transfer rates were also extracted from previous studies in England and Wales. (Table 1) The transfer rates ranged from 11.9 to 43.0%. The weighted mean of all the included studies was 14.3%. As a result, ranges for sensitivity analyses were arbitrarily set as 11.9–43.0%.

Estimation of IPPM rates for home birth

The sensitivity analyses were used to estimate the number of births occurring in both the early and late periods for women in:

• 1
  The completed home birth group.
• 2
  The transferred group.
• 3
  The unintended home birth group.
• 4
  All booked home births group (Table 2).

Table 2.  IPPM, births, IPPM rates for home birth and for overall births in England and Wales (1994–2003)

	All period (1994–2003)
	IPPM	Births	IPPM rate per 1000 births
The estimated values and ranges from the sensitivity analyses are in bold. Numbers obtained by calculation B are in brackets.
Overall	4991	6 314 315	0.79 [0.77–0.81]
Home birth
Actual home birth [95% CI]	125	130 700	0.96 [0.79–1.03]
Booked home birth	96	75187 (128931)	1.28 (0.74)
Range		65276–126114 (94600–194958)	0.76–1.47 (0.49–1.01)
Subgroups
Completed home birth group	31	64435 (110494)	0.48 (0.28)
Range		57508–71885 (83343–111126)	0.43–0.54 (0.28–1.15)
Transferred group	65	10752 (18437)	6.05 (3.53)
Range		7767–54229 (11257–83832)	1.20–8.37 (0.78–5.77)
Unintended home birth group	94	66265 (20206)	1.42 (4.65)
Range		58815–73192 (19574–47357)	1.28–1.60 (1.98–4.80)

The IPPM rate was calculated using the estimated number of births for each subgroup.

In all years, compared with the overall IPPM rate (0.79 per 1000 births [95% CI 0.77–0.81]), the completed home birth group has lower IPPM rate of 0.48 (A) (0.28 for B) per 1000 births with range of 0.43–0.54 (0.28–1.15), while the unintended group of 1.42 (4.65) per 1000 births with range of 1.28–1.60 (1.98–4.80) had higher rates. The rates for transferred group were 6.05 (3.53) per 1000 births with range of 1.20–8.37 (0.78–5.77). There was no evidence of difference in the IPPM rate for the booked home birth group 1.28 (0.74) per 1000 birth with range of 0.76–1.47 (0.49–1.01) compared with the overall rate.

Trend of IPPM for the both actual and booked home birth groups in each study year was plotted in Figure 2, assuming the same weighted means of transfer rate and unintended home birth rate above. There was some evidence of an increase over the years for IPPM for booked home group (the dotted red line, test for trend: P < 0.01).

Discussion

The limitations of this study are as follows:

Data collection

It was considered important to examine the IPPM ratio for all available years in the UK, for two reasons: (a) trend by years was considered important and (b) limitations of the data and data analysis were already anticipated due to lack of reliable/detailed national transfer rates.

Ideally, IPPM rates for women who intended their birth to be in their home at the beginning of labour should be compared with those of women with the same level of risk who intended their birth in hospital at the beginning of labour. However, in any current national surveillance system including that of CEMACH at the time the study was conducted, IPPM rates for such women were not available.¹⁵ The only reliable available data on IPPM rates for women who intended home birth were from CEMACH, and their definition of intended home birth was intended home birth at booking. Therefore, we decided to use booked home birth from CEMACH as the numerator of our study is the best available data.

Demographic characteristics of the study population cannot be obtained because of the different definitions used between data collection systems including CEMACH, National Statistics and previous studies to obtain transfer rates and unintended birth rates.

Measurement errors

The numbers of births occurring overall and at home were derived from national statistics. Miscoding or missing values are therefore considered to have been possible but negligible considering the size of the sample.¹⁵

The numerators (IPPM) were derived from routinely collected data in the CEMACH (previously CESDI) programme, which have been validated against national statistics. There remains the possibility of miscoding, misclassification and missing values, although the data collection system is well established.

Unintended home birth rates and transfer rates were taken from studies previously conducted in England and Wales. The range in these rates is large, and this implies that the studies applied different definitions of transfer and unintended home birth rates. However, the details of the definitions were not available. There were insufficient adequate reports to obtain more precise estimates for these rates, and they were considered the best available. Although the transfer that occurred in the study period was considered as that from home to hospital, there were a few women who booked home birth but whose actual place of birth and outcome of the birth were unknown.

Two methods to obtain unintended home birth have been used to try and explore all possible levels of risk. Calculation A is the most accepted method but because figures calculated as a percentage of all births were available, these were used too and the sensitivities combined. It should be noted that these percentages varied considerably.

Bias

Selection bias could be introduced because only the 10-year period, 1994–2003, was evaluated. These study years were selected because the CEMACH data were available for these years. There was no sampling procedure involved, and the data were based on the whole population of England and Wales.

Selection bias could be introduced for the studies that reported both unintended home birth and transfer rates. These were conducted between 1977 and 1994, before the time period in this study. Not all of the studies reported results for all of England and Wales and half of the six included studies were conducted in the Northern Region. However, although there was neither evidence of a temporal trend in rates nor any obvious regional effect, there is still a possibility of selection bias.

Data were collected after birth, and intended place of birth at booking were recorded retrospectively. This means that recall bias may have been introduced.

Confounding

Background obstetric and medical risk is highly likely to have been different between the groups, and these confounding factors would be likely to have influenced the outcomes, including IPPM. Current practice in the UK means that women with known risk factors are likely to be advised to book for a hospital birth and previous studies support this.^2–7,17 White women, those with multiparity and those in higher social economic status, are more likely to book a home birth^2–7,17 than those from ethnic minority groups, with nulliparity and of lower social economic status. This means that a lower IPPM rate would be anticipated among the women who book home births compared with hospital births.

Data had been anonymised, and it was not possible to remove data for women who had had more than one birth in the study period including multiple births. Some regions may have had higher home birth rates with lower IPPM rates. We considered these as a potential effect modifier, rather than a confounding factor, and unlikely to be relevant to the interpretation of these results.

However, the potential for confounding means that the results of the present study must be interpreted with caution.

Possible explanations

The improvement in overall IPPM rates could result from advances in clinical care, and possibly changes in labour ward management, including improvements in staffing levels and training. For example, the fourth CESDI report (1994–95)²⁰ reported the poor quality of the interpretation of intrapartum fetal heart rate traces and highlighted the need for better education in this area (e.g. introduction of cardiotocograph training).

However, there was a trend to an increased IPPM rate for booked home birth over the study years. Thus, although those women who had intended to give birth at home and did so had a generally good outcome, those requiring transfer of care appeared to do significantly worse and indeed had IPPM rates well in excess of the overall rate. It is not possible to tell from the available data when transfer occurred, that is during pregnancy or at labour onset.

Implications for research and clinical practice

These data have substantial limitations and should be treated with caution. However, the analyses used the best data currently available and certainly indicate the need for further prospective research to evaluate the relative safety of home birth.

There are two main concerns. First, no improvement in the IPPM rates in booked home births was observed, whereas overall IPPM rates did appear to improve. Second, women who booked a home birth but required transfer had relatively high IPPM rates. This needs to be evaluated and investigated further.

It is vital that data are collected prospectively so that an accurate picture can be established of both intended and unintended home birth rates, together with a clear indication about when and why a transfer to hospital care occurred. The fact that reliable data are not currently available to inform a key health debate is a matter of great concern.

In the meantime, appropriate clinical governance should be applied to any of the place of birth setting including home birth.

Acknowledgements

We appreciate and thank CEMACH for providing us with access to aggregated data for analysis. We appreciate Dr Peter Brocklehurst (National Perinatal Epidemiology Unit), Prof Rona McCandlish (National Perinatal Epidemiology Unit and National Collaborating Centre for Women’s and Children’s Health Board), Prof Pat Doyle (London School of Hygiene and Tropical Medicine), Dr Moira Mugglestone (National Collaborating Centre for Women’s and Children’s Health), Dr Paul C. Taylor (the University of Hertfordshire) and Miss Kate Fleming (CEMACH) who reviewed this paper and provided us with valuable comments. This work was undertaken by R.M., M.D. and M.W. at National Collaborating Centre for Women’s and Children’s Health, which received funding from the National Institute for Health and Clinical Excellence. The views expressed in this publication are those of the authors and not necessarily those of the Institute.