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National Collaborating Centre for Women's and Children's Health (UK). Intrapartum Care: Care of Healthy Women and Their Babies During Childbirth. London: RCOG Press; 2007 Sep. (NICE Clinical Guidelines, No. 55.)

  • This publication is provided for historical reference only and the information may be out of date.

This publication is provided for historical reference only and the information may be out of date.

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Intrapartum Care: Care of Healthy Women and Their Babies During Childbirth.

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Appendix DNCC-WCH analysis to obtain the best estimate of intrapartum-related perinatal mortality in England and Wales

Background

A systematic review on risks and benefits of home birth showed increased intrapartum-related perinatal mortality (IPPM) in planned home birth groups in one Australian study30 but no other study has been sufficient to address this issue. The Guideline Development Group was concerned about the lack of UK data and requested the NCC-WCH to conduct an analysis to obtain the best estimate of the IPPM rate in the UK.

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. For the purpose of the study, the years were divided into two equal periods: an early period (1994–1998) and a late period (1999–2003). The cut-off, which made both periods equal in length, was arbitrary and not based on any particular clinical implications.

Definitions

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

  • IPPM rate:
    • – The IPPM rate is defined as deaths from intrapartum ‘asphyxia’, ‘anoxia’ or ‘trauma’, derived from the extended Wigglesworth classification 3,600 which is used by CEMACH.607,608 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 includes women who intended a home birth at booking but 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.
  • Unintended home birth rate and transfer rate:
    • – The unintended home birth rate is the proportion of unintended home births among the total of actual home births.
    • – The transfer rate is the proportion of all women who intended a home birth at booking but who gave birth in hospital or elsewhere, among the total of women who intended a home birth at booking. The transfer includes those that occurred during pregnancy as well as in labour.
  • Completed home birth group, unintended home birth group and transferred group (subgroups of home birth):
    • – Completed home birth group refers to women who intended to have a home birth at booking and had babies at home.
    • – Unintended home birth group refers to women who did not intend to have a home birth at booking but had babies at home.
    • – Transferred group refers to women who intended to have a home birth at booking but had babies in hospital or elsewhere.

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, which collects data for all deaths by intended place of birth at booking.608

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, The Cochrane Library, EMBASE, BNI, CINAHL and MIDIRS), using keywords such as ‘home birth’ and reference lists of relevant articles. Inclusion criteria stipulated that studies:

  • were conducted in the UK
  • were population based, which was defined as a study that reflects women at low risk in a certain defined area
  • used 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 booked home birth.

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.19,20,609–617

Denominators (birth numbers) for booked home birth

The number of births from the Office for National Statistics, which relates to the actual place of birth, has been modified by removing the unintended home births and then adding back the likely transfers to provide an estimated number of women who had an intended home birth at booking.

Statistical analysis

IPPM rates were calculated from the data described above.χ2 tests were performed to test for trends and applied to a comparison of IPPM rates when appropriate. Confidence intervals were also calculated when appropriate. Sensitivity analyses were performed using the pre-set ranges derived from previous studies.

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 improved significantly during this period (test for trend: χ2 value = 100.92, degrees of freedom = 1, P < 0.001). The IPPM rate for the late period (0.68 per 1000 births [95% CI 0.65 to 0.71/1000]) was significantly lower than that for the early period (0.90 per 1000 births [95% CI 0.86 to 0.93/1000]) (χ2 value = 100.09, degrees of freedom = 1, P < 0.001; data not shown).

IPPM rate for actual home births

There were 75 intrapartum-related deaths among the 66 115 home births in England and Wales in the early period, while 50 intrapartum-related deaths occurred in the 64 585 home births in the late period. The IPPM rate of 0.77 per 1000 births [95% CI 0.56 to 0.99/1000] for the later period was significantly better than the rate of 1.13 per 1000 births [95% CI 0.88 to 1.39/1000] (χ2 value = 4.43, degrees of freedom = 1, P = 0.04) for the early years. The IPPM rate for actual home births in the early period was significantly higher than that for all births (χ2 value = 4.04, degrees of freedom = 1, P = 0.04), but there was no evidence of difference in IPPM rates between actual home birth and all births in the later period (χ2 value = 0.90, degrees of freedom = 1, P = 0.34).

Unintended home birth rates from previous studies

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

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

Table D.1

Unintended home birth and transfer rates from previous studies conducted in England and Wales.

The unintended home birth rates ranged from 45.0% to 56.0%. The weighted mean of all the included studies was 50.7%. As a result, ranges for sensitivity analyses were set as 45% to 56%.

Transfer rates from previous studies

Transfer rates were also extracted from previous studies in England and Wales (Table D.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% to 43.0%.

Estimation of IPPM rates for home birth

The sensitivity analyses (Table D.2) were used to estimate the number of births occurring in both the early and late periods for women in:

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

Table D.2

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

  • the completed home birth group
  • the transferred group
  • the unintended home birth group
  • the booked home birth group.

The IPPM rate was calculated using the estimated number of births for each subgroup (Table D.2).

In the early period, the completed home birth group had a lower IPPM rate (0.46 per 1000 births [range 0.41 to 0.52]), while both the unintended home birth group (1.79 per 1000 births [range 1.62 to 2.02/1000]) and the transferred group (5.52 per 1000 births [range 1.92 to 8.67/1000]) had higher rates compared with the overall IPPM rate. In the early period, there was no evidence of a difference in IPPM rate between the booked home birth group (1.18 per 1000 births [range 0.71 to 1.36/1000]) and the overall IPPM rate.

In the late period, a similar pattern was observed, with the completed home birth group having a lower IPPM rate (0.50 per 1000 births [range 0.45 to 0.56/1000]), and both the unintended home birth group (1.04 per 1000 births [range 0.94 to 1.17/1000]) and the transferred group (6.59 per 1000 births [range 1.31 to 9.12/1000]) having higher IPPM rates, compared with the overall IPPM rate. However, in the late period, the IPPM rate of the booked home birth group (1.37 per 1000 births [range 0.82 to 1.58/1000]) seemed to be higher than the overall IPPM rate and this was presumably due to the increased IPPM in the transferred group.

Although improvement was observed in the overall IPPM rates, none was seen when the results for booked home births from the late period were compared with those in the early period. The findings were similar for both the completed home birth group and the transferred group.

Discussion

The limitations of this study are considered below.

Measurement errors

The numbers of births occurring overall and at home were derived from national statistics. Miscoding and missing values are therefore considered to have been possible but negligible considering the size of the sample.19,20

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 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 with unknown consequences of their actual place of birth in the CEMACH data. This may have influenced the high IPPM rates in the transferred group. A sensitivity analysis ranging from less than the lowest obtained rate to greater than the highest obtained rate was used in an attempt to compensate for this uncertainty.

Bias

Selection bias could be introduced because only the 10 year period of 1994–2003 was evaluated. The study years were selected because the CEMACH data were available for these years. There might have been further changes since 2003, as there were changes observed between the early and later years. Otherwise, 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 three 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 the intended place of birth at booking was 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.29,31,32,34,35,39,42 White women, those with multiparity and those in higher socio-economic groups are more likely to book a home birt h29,31,32,34,35,39,42 than those from other ethnicities, with single parity and of lower socio-economic status. This means that a lower IPPM rate would be expected 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 have resulted from advances in clinical care, including use of more sophisticated strategies for identifying and acting upon risk, or improvements in staffing levels and training. For example, the fourth CESDI report (1994–1995)608 reported the poor quality of the interpretation of intrapartum fetal heart rate traces and highlighted the need for better education in this area.

However, the IPPM rate for booked home birth in the late period appeared to be higher than the overall IPPM rate and had not improved from the early period and this seemed to arise from the worsening of the outcome in the transferred group over the two periods. 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, i.e. whether during pregnancy or at labour onset.

Acknowledgments

We appreciate and thank CEMACH for providing us with access to aggregated data for analysis.

We are also grateful to Dr Peter Brocklehurst (National Perinatal Epidemiology Unit), Professor Rona McCandlish (National Perinatal Epidemiology Unit and National Collaborating Centre for Women’s and Children’s Health Board), Professor Pat Doyle (London School of Hygiene & Tropical Medicine), Dr Paul C Taylor (University of Hertfordshire), Dr Moira Mugglestone (National Collaborating Centre for Women’s and Children’s Health) and Miss Kate Fleming (CEMACH) who reviewed this paper and provided us with valuable comments.

Copyright © 2007, National Collaborating Centre for Women’s and Children’s Health.

No part of this publication may be reproduced, stored or transmitted in any form or by any means, without the prior written permission of the publisher or, in the case of reprographic reproduction, in accordance with the terms of licences issued by the Copyright Licensing Agency in the UK [www.cla.co.uk]. Enquiries concerning reproduction outside the terms stated here should be sent to the publisher at the UK address printed on this page.

The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant laws and regulations and therefore for general use.

Bookshelf ID: NBK49380

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