August 30, 2009
A new era of home birth research
By: Amy M. Romano, RN,CNM | 0 Comments
In preparing the Home Birth chapter for the forthcoming second edition of Obstetric Myths versus Research Realities, I have literally just finished reading the entire body of literature on planned home birth. Just last week, I said to my co-author, Henci Goer, 'frankly, I'm pretty underwhelmed by the quality of most of the studies.' (Though, don't get me wrong, I still believe that the preponderance of the evidence strongly favors the choice of planned home birth.) But for the second time this year, an exemplary study on planned home birth has been released. Together with the Dutch study released in April, the current study ushers in a new era of home birth evidence that addresses many of the methodological limitations of previous home birth research. Seriously, folks, these two studies raise the bar.
Researchers in Canada analyzed the outcomes of all women who were intending to give birth at home at the onset of labor in British Columbia between 2001-2004 (n=2899 women). Data were obtained from the provincial database that collects information on all births and is cross-referenced with the national vital statistics (birth/death certificates) database. The researchers compared outcomes in the planned home birth group with those of two groups of women who met eligibility requirements for home birth but planned to give birth in hospitals instead. One of the two comparison cohorts had planned hospital births with midwives (n=4752); the other with physicians (n=5331).
Consistent with many other studies comparing planned home with planned hospital birth, the results showed comparable perinatal mortality rates, less serious morbidity for both women and infants, and lower use of obstetric technology in planned home births. Here are the results, as presented in the study's abstract:
The rate of perinatal death per 1000 births was 0.35 (95% confidence interval [CI] 0.00'1.03) in the group of planned home births; the rate in the group of planned hospital births was 0.57 (95% CI 0.00'1.43) among women attended by a midwife and 0.64 (95% CI 0.00'1.56) among those attended by a physician. Women in the planned home-birth group were significantly less likely than those who planned a midwife-attended hospital birth to have obstetric interventions (e.g., electronic fetal monitoring, relative risk [RR] 0.32, 95% CI 0.29'0.36; assisted vaginal delivery, RR 0.41, 95% 0.33'0.52) oradverse maternal outcomes (e.g., third- or fourth-degree perineal tear, RR 0.41, 95% CI 0.28'0.59; postpartum hemorrhage, RR 0.62, 95% CI 0.49'0.77). The findings were similar in the comparison with physician-assisted hospital births. Newborns in the home-birth group were less likely than those in the midwife-attended hospital-birth group to require resuscitation at birth (RR 0.23, 95% CI 0.14'0.37) or oxygen therapy beyond 24 hours (RR 0.37, 95% CI 0.24'0.59). The findings were similar in the comparison with newborns in the physician-assisted hospital births; in addition, newborns in the home-birth group were less likely to have meconium aspiration (RR 0.45, 95% CI 0.21'0.93) and more likely to be admitted to hospital or readmitted if born in hospital (RR 1.39, 95% CI 1.09'1.85).
What makes this study stand out from most of the rest:
1. Planned home births occurred in a context with relatively rigid guidelines for eligibility (see the full-text of the article to view the guidelines). These guidelines, determined by the Ministry of Health, were applied to women planning hospital births in order to construct the comparison cohorts. This increases the likelihood that, medically at least, the populations were similar. In addition, participants in the home birth group were matched with participants in the physician-attended hospital birth for the following parameters: year of birth, parity, single parent (yes or no), maternal age, and the hospital where the midwife conducting the index home birth had hospital privileges.
2. The authors made the cohorts more similar with statistical analysis ' first, controlling for confounding variables and second, testing and retesting their data with different assumptions and exclusions. (Referred to as 'sensitivity analysis,' this is a mechanism used by researchers to make sure their findings hold up under various circumstances and are unlikely therefore to be biased.)
3. The researchers isolated the effect of the birth setting itself by comparing midwife-attended home birth with midwife-attended hospital birth. In fact, the same group of midwives cared for women in both settings, so differences are likely to be related to the setting and its protocols and technological accoutrements (or lack thereof) rather than differences in the providers who actually provide the care.
4. According to the study authors, midwives in British Columbia are required to offer medically eligible women a choice of planned home or hospital birth. While women still must self-select to one choice or another, this certainly mitigates some bias. Self-selection bias refers to the possibility that individuals who, in this case, select different birth settings or providers, may be different in ways that are not measured but that nonetheless affect the likelihood of important outcomes. For example, women who choose home birth may have better nutrition, stronger family support systems, or a more positive outlook on labor and birth. But these differences may be less pronounced when the group selecting home birth showed up at the same prenatal clinic as all of the rest of the women and were (perhaps enthusiastically) presented the option of birthing at home. Contrast this with the population of women in parts of the United States who must actively seek out home birth, pay out of pocket, and be told that no physician will willingly consult if medical problems arise so they must settle for the emergency room, whether or not the transfer to the hospital is urgent. (The vast majority of transfers from home to hospital are not.) Only the most dedicated are likely to choose such an option.
5. Although the study was retrospective (meaning data were collected after the fact), data were obtained from province-wide databases to which care providers are obligated to enter data on each and every birth. In addition, these databases have been tested for the reliability of the data (to detect the possibility that certain outcomes are systematically underreported or overreported). Reliability was above 97% for all outcomes. Fewer than 1 in 10,000 records were missing. *
The only thing I did not see in the report that I would have liked to is a detailed description of the circumstances of each fetal or newborn death. These descriptions often provide clues as to whether small differences in perinatal mortality could have been attributed to the planned place of birth and whether and how they might have been averted.
No study of home birth will be perfect, but large perinatal databases and systems that integrate rather than marginalize home-birth midwifery have helped to achieve the 'scientific rigor' that the American College of Obstetricians and Gynecologists has called for. And the results are looking very good indeed.
* denotes edited text. Click 'read more' to view the original version. Edited September 2 at 10:57pm due to error in original (see comment by @desiree and my response.) Deleted text: And although data, including the intended place of birth, are submitted after the baby is born, the researchers present compelling evidence that perinatal mortality rates are reliable regardless. They note that even had all of the perinatal deaths occurring in the midwife-attended hospital cohort actually occurred in women intending to birth at home (but reported in the database to have planned hospital births), the perinatal mortality rate among women planning home birthincluding these deaths would still have been lower than the rate in the physician-attended hospital cohort.
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