September 25, 2013
Flaws In Recent Home Birth Research May Mislead Parents, Providers
By: Sharon Muza, BS, LCCE, FACCE, CD/BDT(DONA), CLE | 0 Comments
by Wendy Gordon, CPM, LM, MPH, MANA Division of Research, Assistant Professor, Bastyr University Dept of Midwifery
Midwife Wendy Gordon shares with Science & Sensibility readers why the recent home birth research using 5 minute Apgar scores does not produce reliable data that consumers can use to make a decision on where they would like to give birth. Have you had a chance to read the study? What were your conclusions? See if you agree with Wendy or had some different thoughts. Share your opinion and thoughts with us in the comments section. Thank you Wendy for providing information that can help us to assess the study and understand it better. - Sharon Muza, Science & Sensibility Community Manager
A recent press release by the authors of a new study raised alarming headlines in a few media outlets, suggesting that babies born at home had a 10-fold higher death rate than babies born in the hospital. I've written previously about reliability concerns with the use of birth certificates in this study. In this post, we'll go more in-depth with some of its other flaws. Let's start with the fact that the authors did not examine stillbirths.
Apgar scores and stillbirth
The new study by Grunebaum et al. (2013), in press with the American Journal of Obstetrics & Gynecology, examined birth certificate data for almost 14 million births between 2007 and 2010 looking for differences in outcomes between home and hospital births. They did not look at 'stillbirths,' perinatal, intrapartum or neonatal deaths. They looked at 5-minute Apgar scores of zero, and led the readers of their press release to believe that this meant that the babies died during or shortly after labor, due entirely to their choice of birthing at home.
When we examine a little more closely what it means to have a 5-minute Apgar score of zero, we might find that it does include some babies who died shortly after birth. We might also find a number of babies who had lethal congenital anomalies, who would not have survived no matter where they were born or who attended the birth; there may be important differences between home and hospital populations with regard to whether these anomalies were detected prenatally and whether parents changed their birth plans because of it. There may also be some babies who were successfully resuscitated after the 5-minute Apgar score was assessed. While the authors conceded in the study that their analysis could have included these births, as well as babies who died before labor even began, the terminology used in their press release is highly misleading.
A rigorous study that actually examined deaths would have excluded births with outcomes that had nothing to do with place of birth or attendant. Several well-designed studies have done just that and have found no differences in mortality rates between planned home and hospital births, and often fewer low 5-minute Apgar scores among planned home births attended by midwives (Ackermann-Liebrich et al., 1996; Olsen, 1997; Janssen et al., 2002; Hutton et al., 2009; Janssen et al., 2009). Grunebaum does not mention that their findings are actually the opposite of what several rigorous studies have already determined.
Absolute vs relative risk
I've also written previously about the dangers of reporting relative risks ('ten times higher!') without acknowledging that the absolute risk of the complication is actually very, very low. Even if Grunebaum's study had appropriately excluded outcomes that had nothing to do with place of birth, and even if their source of data was reliably accurate - no one is served by omitting the fact that 5-minute Apgar scores of zero are exceedingly rare.
Some of the raw numbers that Grunebaum reports in the study are so low ' less than a dozen events within tens of thousands of births, in some cases - that it is hard to imagine how practitioners could use this information to draw any meaningful conclusions whatsoever about clinical practice.
Even with all of the flaws in this study, the rate of zero Apgars in the 'home midwife' category in this study was 1.6/1000. This is a very low number. If these results were valid, it would be these absolute risks that mothers and families should be informed about, and honest discussions should be had regarding why there might be a higher risk in the home setting so that families can make the best decisions for themselves about all of the risks and benefits that come with location of birth.
Transfers not accounted for in 'planned' home births
A concern that is often raised by anti-homebirth activists is that births that start out as planned home births but transfer to the hospital in labor are actually counted as hospital statistics in birth certificate data. To be fair, these births likely do have worse outcomes. Although most transfers are for non-urgent reasons such as stalled labor or desire for pain relief (Johnson & Daviss, 2005), some transfers occur because medical assistance is needed and the appropriate place to be is in the hospital.
But let's look at the real impact of these transports. U.S. data shows that about 10% of planned home births result in transport to the hospital during labor (Johnson & Daviss, 2005). Even if Grunebaum was able to accurately capture planned home births and that number truly was 67,429, we could reasonably assume that about 10% of those babies (6743) were born in the hospital. Those babies account for less than 0.05% of the 14 million babies born in the hospital. Even if every single one of those babies had a 5-minute Apgar score of zero, Grunebaum's rate of zero Apgars in the hospital would increase from 0.25/1000 to 0.49/1000. In reality, only a very small proportion of home birth transports actually do result in such an adverse outcome, and thus essentially have a negligible effect on hospital outcomes.
On the other hand, even a small percentage of misclassified outcomes in the home birth category have a dramatic impact. Because the number of home births in the U.S. is small, the inclusion of prenatal stillbirths, congenital anomalies and unplanned, unattended home births in the 'home midwife' category is likely to have an appreciable effect on the negative outcomes examined here. Furthermore, the 10% of home birthers who transport to the hospital and have positive outcomes there are not appropriately attributed to the planned home birth group either. The truth about the safety of home birth simply cannot be determined in this way.
Reliability of birth certificates
I wrote my initial reaction to Grunebaum et al's study last week when their press release came out. I expressed concerns about the low reliability and validity of birth certificates for drawing conclusions about rare outcomes. Grunebaum's own data shows that over 10% of 'home midwife' deliveries had no information on the birth certificate about the mother's parity and had to be excluded from their calculations, while only 0.2-0.5% of hospital or birth center deliveries were missing parity data; this strongly suggests that something is amiss with the 'home midwife' data.
Epidemiologists and birth certificate scholars have made their concerns about reliability and validity exceedingly clear in an enormous body of literature over the last few decades, and in fact, expressed these concerns directly to Frank Chervenak (co-author on this study) earlier this year when he presented this very data at the Institute of Medicine's workshop on Research Issues in the Assessment of Birth Settings (IOM & NRC, 2013, p.143). The fact that these authors were clearly warned about the low quality of their data regarding both low Apgar scores - and especially seizures - but chose to push ahead with publication without addressing them, suggests other motivations.
Families deserve to have the best possible information with which to make decisions about where to have their babies. Grunebaum and co-authors miss the mark by a wide margin with the methodology and conclusions of this study.
To learn more about existing, well-designed home birth studies, read here. To learn more about the MANA Stats Project, which provides researchers with a dataset of more than 24,000 planned home birth and birth center births, read here. And watch for new research based on the MANA Stats dataset 2004-2009. Two articles are in press and two more are under review in peer-reviewed journals.
Ackermann-Liebrich, U., Voegeli, T., Gunter-Witt, K., Kunz, I., Zullig, M., Schindler, C., Maurer, M. & Zurich Study Team. (1996). Home versus hospital deliveries: follow up study of matched pairs for procedures and outcome. BMJ 313:1313-1318.
Declercq, E., MacDorman, M. F., Menacker, F., & Stotland, N. (2010). Characteristics of planned and unplanned home births in 19 states. Obstetrics & Gynecology 116(1):93-99.
Grunebaum, A., McCullough, L. B., Sapra, K. J., Brent, R. L., Levene, M. I., Arabin, B., & Chervenak, F. A. (2013). Apgar score of 0 at 5 minutes and neonatal seizures or serious neurologic dysfunction in relation to birth setting. Am J Obstet Gynecol, 209:x-ex x-ex.
Hutton, E. K., Reitsma, A. H., & Kaufman, K. (2009). Outcomes associated with planned home and planned hospital births in low-risk women attended by midwives in Ontario, Canada, 2003-2006: a retrospective cohort study. BIRTH 36(3):180-189.
IOM (Institute of Medicine) and NRC (National Research Council). (2013). An Update on Research Issues in the Assessment of Birth Settings: Workshop Summary. Washington, DC: The National Academies Press.
Janssen, P. A., Lee, S. K., Ryan, E. M., Etches, D. J., Farquharson, D. F., Peacock, D., & Klein, M. C. (2002). Outcomes of planned home births versus planned hospital births after regulation of midwifery in British Columbia. CMAJ 166(3):315-323.
Janssen, P. A., Saxell, L., Page, L. A., Klein, M. C., Liston, R. M., & Lee, S. K. (2009). Outcomes of planned home birth with registered midwife versus planned hospital birth with midwife or physician. CMAJ 181(6-7):377-383.
Johnson, K. C. & Daviss, B. A. (2005). Outcomes of planned home births with certified professional midwives: large prospective study in North America. BMJ 330:1416-
Olsen, O. (1997). Meta-analysis of the safety of home birth. BIRTH 24(1):4-13.
About Wendy Gordon
Wendy Gordon, LM, CPM, MPH is a midwife, mother and educator in the Seattle area. She helped to build a busy, blended homebirth practice of nurse-midwives and direct-entry midwives in Portland, Oregon for eight years before recently transitioning to Seattle. She is a Coordinating Council member of the Midwives Alliance Division of Research, a board member of the Association of Midwifery Educators, and teaches at the Bastyr University Department of Midwifery.
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