We want to thank those who have responded to our manuscript. We would like to address the misconception that we were trying to create comparison groups in our study that were equal in obstetrical risk status. Although we tried to ensure that comparison groups met eligibility criteria for home birth, women who choose home birth differ from those who select hospital birth in both measurable and unmeasurable ways. This selection bias is unavoidable. The purpose of our study was not to determine which method of care was better, home vs. hospital, but rather to assess whether, at the 2-year interval, home birth was safe enough to continue to be offered as a choice for women in the context of ongoing evaluation.
Although we have expressed concern about the rates of some outcomes (“babies exposed to thick meconium who are not vigorous at birth may be disadvantaged in the home birth group”), the small numbers of mothers or babies who experienced adverse outcomes cannot justify a recommendation to avoid home birth at this time. We believe that the final statement “these comparisons are based on small numbers and warrant ongoing evaluation” reflect the possibility of a type II error, that is, lack of power to detect differences in some of the rare outcomes in our study.
With regard to Dan Farine's analysis, two of the subjects with obstetrical shock also received blood transfusions so should not be counted twice. Among the babies requiring ventilation >> 24 hours, one was the baby that died during the neonatal period, who similarly should not be counted twice. With respect to perinatal mortality, note that the one perinatal death in the comparison groups occurred not in the group of hospital-intended births attended by midwives, as Farine's table indicates, but in the physician comparison group. No evidence suggests that any of the perinatal deaths in the home birth group were related to labour management at home. Composite outcome scores are normally presented separately for mothers and babies, as outcomes in the two groups are not always independent of each other. In addition, the denominators for the maternal and newborn analyses are different because only outcomes among newborns born without major anomalies were assessed. Although composite outcome scores have greater power than analyses of individual outcomes, we did not specify a composite outcome a priori because of the lack of validated tools relevant to babies born at term.
With respect to tracheal suctioning, we observed that only 45% of babies in the home birth group who were exposed to thick meconium and were not vigorous at birth (Apgar score less than 7 at 1 minute) received tracheal suctioning, compared with 75% in each comparison group. As a result of our observations, the Home Birth Demonstration Project Evaluation recommended to the Ministry of Health that this issue be referred to the Newborn Resuscitation Committee at BC's Children's Hospital. This committee will examine issues related to the expectation and maintenance of competency in tracheal intubation. However, maintenance of competency is a problem common to all health care providers who do not routinely practise intubation. A comprehensive approach to the acquisition and maintenance of intubation skills is needed throughout the province.
As we discussed in our interpretation section, our intrapartum transfer rate of 16.5% was well within published rates.
The small number of adverse outcomes among an essentially healthy population of women limits the power of a single study to make valid conclusions. We look forward to seeing either larger studies of home birth in Canada or pooled results from smaller studies.
Patricia Janssen Assistant Professor Department of Health Care and Epidemiology University of British Columbia Vancouver, BC