And here's the NCT's response to it:
Mori et al study on the safety of planned home births
There are fundamental weaknesses in the design of the Mori et al
study on the safety of home birth published in the BJOG today. There
are also some errors and inconsistencies in the calculations used
within the chosen design. The results carry a health warning from
the authors, who say "These data have substantial limitations and
should be treated with caution". We would say that they are
unreliable and may be seriously misleading.
To assess the safety of home birth accurately, prospective data is
needed. That is data collected for the purpose of the study, going
forwards in time, following women through their care and recording
outcomes for them and their baby.
This study is retrospective using data from several different
studies and from databases compiled for other purposes. There may be
problems of missing data, mis-coded cases and recall bias.
To compare the safety of planned home births with planned hospital
births it is vital to have similar samples of women, and to exclude
unplanned home births. Unplanned home births have much poorer
outcomes than planned home births as women who conceal their
pregnancies are often unattended in labour and have had no antenatal
care.
In this study, Mori et al make a series of estimates about unplanned
home births and intra-partum related perinatal mortality (IPPM)
rates, applying estimates from previous studies to two unrelated
datasets. In particular, the estimates of unplanned home births are
unreliable. Two different methods have been used to calculate
unplanned home births: one of these estimates of around 66,000
(calculation A) is three times higher than another estimate of
20,000 (category B). A paper published in the BMJ by Murphy et al,
over 20 years ago showed calculation B to be more reliable, yet Mori
et al base their conclusions of calculation A. If estimates of IPPM
are based on calculation B then IPPM associated with home birth is
not different from rates for all births (home birth 0.74 per 1000
births; all births 0.79 per 1000 births).
Women who transfer to hospital
The Mori et al paper quotes an increased estimated IPPM rate for
women who plan a home birth but transfer to hospital. There are
three key problems with this:
? These are very rough and inaccurate estimates. The paper
does not make it clear that the calculation of 6 baby deaths per
1000 women transferred is a rough estimate, not a precise number.
The range using two different calculations was anything from 0.78 to
8.37 deaths per 1000 births. To put this in context, the rate for
all births was 0.79 per 1000 births.
? Over half of the women from the three research studies used
by Mori et al to calculate the estimate rate of baby deaths
transferred before the start of labour, so they had all their labour
care in hospital.
? A higher complication rate would be expected for women whose
pregnancy is not straightforward, but there is no means of comparing
the women planning a home birth (who, for example, might develop pre-
eclampsia, or have twins, or have a breech baby) with similar women
planning a hospital birth. Women booked for hospital care with these
kinds of risk factors will also have a higher complication rate than
other women (though no data is provided by Mori et al to allow
comparison).
Fortunately the Birthplace study is underway to address these issues
in a prospective study designed specifically to address these
issues. Everyone should avoid jumping to premature conclusions
before this study is completed. (www.npeu.ox.ac.uk/birthplace).