67
BIRTH 40:1 March 2013
IN THE LITERATURE COMMENTARY ON: Picklesimer AH, Billings D, Hale N, Blackhurst D, Covington-Kolb S. The effect of CenteringPregnancy group prenatal care on preterm birth in a low-income population. Am J Obstet Gynecol 2012;206:415.e1–415.e7.
Does the CenteringPregnancy Group Prenatal Care Program Reduce Preterm Birth? The Conclusions Are Premature Neal F. Devitt, MD, FAAFP ABSTRACT: Prenatal care is promoted as a means to a healthy pregnancy outcome. In the United States great resources have been spent to expand the availability of a program of prenatal care, but without evidence for its effectiveness in the general population. Despite greater access to prenatal care over the last several decades, there has been no improvement in obstetric outcomes, such as preterm delivery. The CenteringPregnancy program of group prenatal visits is a novel form of prenatal care that, according to several studies, has been said to improve satisfaction with prenatal visits and with pregnancy outcomes. A careful reading of the studies shows that those goals are yet to be achieved. Innovation is welcome and essential, but larger studies are needed to achieve statistical significance to demonstrate improved outcome. (BIRTH 40:1 March 2013)
Key words: prenatal care, group prenatal care, CenteringPregnancy, pregnancy The United States appears to be emerging from the midst of a preterm birth epidemic (1). The preterm birth rate rose by more than one-third from 1981 to 2006, and although at its lowest level in more than a decade, the 2011 rate is still higher than rates reported during the 1980s and most of the 1990s. In 2011 more than 1 in 10 babies were born preterm. All practitioners and policymakers would agree that this preterm birth rate is too high and is a public health crisis. The cost of medical care for babies born significantly preterm is much greater than that for babies born at term, and the Neal F. Devitt is Senior Physician at the La Familia Medical Center, a Community Health Center, and Faculty member at The Northern New Mexico Family Medicine Residency, Santa Fe, New Mexico, U.S.A. Address correspondence to Neal Devitt, MD, La Familia Medical Center, 1035 Alto Street, Santa Fe, New Mexico 87505, USA.
© 2013, Copyright the Authors Journal compilation © 2013, Wiley Periodicals, Inc.
physical and intellectual disabilities that many of them carry on to adulthood are a great burden to the child, the family, and society. Prenatal care is promoted as a means to a healthy pregnancy outcome. However, to this day there is no evidence that prenatal care, as it is currently structured, is effective in improving the health of the childbearing population and the outcome of their pregnancies (2,3). Prenatal care is a relatively modern concept, first developed in the British Isles in the late 1800s and imported into the United States in 1908 (4). It was promoted by J.W. Williams (5) in his seminal 1914 JAMA article, “The Limitations and Possibilities of Prenatal Care,” as a means to identify and possibly treat complications of pregnancy, such as eclampsia and syphilis. At that time the physician did little more prenatally than monitor blood pressure and proteinuria. Much of what we consider to be prenatal care was delivered in the home of the expectant mother by public health nurses. J.W. Williams’ prenatal instructions comprise
68 one page of his text (5). The pregnant woman is asked to send to his office a urine sample monthly for the first 7 months then biweekly for the remainder of her pregnancy. She is to call for bleeding and for signs of preeclampsia, but otherwise call the public health nurse at the beginning of labor and “let her use her judgment in sending for me.” (6, p 210). In the 1920s, the federal Children’s Bureau (7) first tried to standardize content of prenatal care (measurement of blood pressure, proteinuria, weight, and fundal height), using a form that may be still familiar to “more seasoned” physicians and midwives. In the 1930s and 1940s, physician groups campaigned to move the site of prenatal care from the domain of the public nurse in the family home to the physician in his office. Once established in the physician office, prenatal care exhibited little change from the 1940s to recent years. In the 1970s regionalization of perinatal care was promoted. In the 1980s two reports by the United States government, Caring for Our Future (8) and Preventing Low Birth-Weight (9) provided the impetus for increased funding of the federal Medicaid program for low-income women. The number of pregnant women covered by Medicaid rose from 17 percent in 1985 to 35 percent in 1998. However, no evaluation of its effectiveness or promulgation of any more effective models was conducted. Thus, Kogan et al concluded that, between 1981 and 1995, the use of prenatal care increased without any improvement in rates of preterm birth and low birthweight (10). Indeed, “too much” prenatal care may worsen outcomes (11). A recent review, “Two Hundred Years of Progress in the Practice of Midwifery,” focused mainly on the adoption of new technology without mentioning Williams’ efforts to develop and promote prenatal care, perhaps because it was published not in the Journal of the American Medical Association but in a competing journal (12). It is in this context that the paper “The effect of CenteringPregnancy group prenatal care on preterm birth in a low-income population”(13) is important. Picklesimer et al expand on the work by Ickovics et al (14), evaluating the CenteringPregnancy model of prenatal care. “Centering is a model of group health care that is changing how people think about their care. The model has three components: health assessment, education, and support, provided in a group facilitated by a health care provider” (15). This proprietary program uses group prenatal visits in which “Eight to twelve women with similar gestational ages meet together, learning care skills, participating in a facilitated discussion, and developing a support network with other group members. Each Pregnancy group meets for a total of 10 sessions throughout pregnancy and early postpartum. The practitioner, within the group space, completes standard physical health assessments” (15).
BIRTH 40:1 March 2013
Ickovics et al (14) and Picklesimer et al (13) are to be commended for putting forth a different model for prenatal care, and actually evaluating its effects on pregnancy outcome. However, I have several concerns about the program and the paper by Picklesimer et al. In their introduction as rationale for their study, the authors (13) reference Ickovics et al’s previous study (14), writing “the rate of preterm birth among women in group care was 33% lower than the rate of preterm birth for women in the traditional prenatal care control group.” This claimed benefit of CenteringPregnancy group visits needs further evaluation. Ickovics et al evaluated both clinical (preterm birth), process (number of prenatal visits) and nonclinical (patient knowledge and satisfaction) outcomes (14). I shall focus largely on the clinical outcomes. Comparing 623 women randomized to group care with 370 women in traditional care, they found no significant difference in gestational age (reported by week), low birthweight, mean birthweight, neonatal intensive care unit admission, or total cost of prenatal care (available for only one of the two study sites). The claimed reduction in preterm birth was only a reduction in births before 37 completed weeks (i.e., before 259 days). There are important differences between the earlier study of Ickovics et al (14) and the paper by Picklesimer et al (13). In the study of Ickovics et al (14) the population was 80 percent black, whereas the population studied by Picklesimer et al (13) was about onethird black, one-third non-Hispanic white, one-sixth white Hispanic, and one-sixth other, giving the results more generalizability. Weaknesses are the study’s retrospective design and the self-selection of the intervention group. In addition, data were collected from electronic birth certificate database worksheets, which, according to the authors, “do not include information about the presence or absence of many of the high-risk conditions that would have excluded women from participation in our group prenatal care program such as maternal cardiac or renal disease” (13). In addition, fewer of the nulliparous women in group care used tobacco, and 15 percent of the study group withdrew from group visits. These caveats aside, again the CenteringPregnancy program is said to have reduced preterm births by 47 percent. The percentage of very preterm births (less than 32 weeks of gestation) was also reduced, but without significant improvements in actual clinical outcome. Mean birthweight was larger by 67 g, but no significant difference was observed in low birthweight (less than 2,500 g) or in neonatal intensive care unit admission. It is also important to realize that both these studies included more than one intervention. The CenteringPregnancy curriculum is one intervention and group care is another intervention, but they are lumped together. We
69
BIRTH 40:1 March 2013
do not know whether beneficial effects resulted from the curriculum or simply from some independent effect of group visits. Although unlikely, a beneficial effect on pregnancy outcome as a result of a pheromone effect of group proximity cannot be completely excluded (e.g., similar to McClintock’s description of menstrual synchrony in a women’s college dormitory (16,17). More likely, women in a group could share resources and strategies that could have a positive effect on pregnancy outcome independent of any curriculum. Analogously, prenatal clients of community health centers, despite their poverty, have a lower percentage of low birthweight babies than the United States population as a whole (18). This outcome is thought to be the result of the broad array of social resources available through community health centers (19). I have not addressed the nonclinical outcomes, which are substantial. The stated increase in patient knowledge and satisfaction has the potential to improve the outcome of future pregnancies. I would look forward to a study evaluating the outcome of future pregnancies in women in this study group who receive the usual prenatal care in a subsequent pregnancy compared with a control group who never received group care to evaluate whether these benefits are sustained. The interested reader may refer to Hollowell et al (20) for a review of the effectiveness of other interventions in prenatal care. Although, not traditionally considered to be prenatal care, a program of antenatal and postnatal home visits with a set curriculum developed by Olds et al was shown to reduce rates of low birthweight (21). CenteringPregnancy may indeed be able to lower the preterm birth rate. The small size of these studies is another limitation—a limitation that may preclude statistical significance. Too many studies published in the obstetric literature include substantially fewer than 1,000 women, a size that is unlikely to demonstrate benefit from an intervention in the United States, given the relatively low frequency of many obstetric complications. Major studies of treatments of cancer or cardiovascular disease routinely include tens of thousands of patients and multiple academic centers, and often span continents. When we study effective programs for maternity care, we are investing in our future. Large studies are costly. It is not enough to critique studies for being too small. We must also ask why we do not have the resources for larger studies. The average age of a U.S. Senator is 62 years and the average age of a Representative is 57 years. Eighty-three percent of our Congresspeople are white and 83 percent are male. These are the people who are more motivated to fund studies of cancer and cardiac disease. To improve research on effective prenatal care, perhaps we need to elect more women of reproductive age to Congress.
References 1. Hamilton BE, Martin JA, Ventura SJ. Births: Preliminary data for 2011. Natl Vital Stat Rep 2012;61(5):5–6. 2. Krans EE, Davis MM. Preventing Low Birthweight: 25 years prenatal risk, and the failure to reinvent prenatal care. Am J Obstet Gynecol 2012;206:398–403. 3. Alexander GR, Kotelchuck M. Assessing the role and effectiveness of prenatal care: history, challenges, and directions for future research. Public Health Rep 2001;116:306–316. 4. West M. The growth of prenatal work in this country. Trans Am Assoc Study Prevention Infant Mortal 1914;5:69–108. 5. Williams JW. The limitations and possibilities of prenatal care. JAMA 1915;64:95–101. 6. Williams JW. Obstetrics. New York and London: D Appleton and Co, 1912. 7. De Normandie RL. Standards of Prenatal Care: An Outline for the Use of Physicians. Publication No. 153:9-10. Washington, DC: Children’s Bureau, 1925. 8. Rosen MG, Culpepper L, Goldenberg R, et al. Caring for Our Future: The Content of Prenatal Care. A Report of the Public Health Service Expert Panel on the Content of Prenatal Care. NIH Publication No. 90-3182. Washington, DC: U.S. Department of Health and Human Services, 1989. 9. Institute of Medicine. Preventing Low Birth-Weight. Washington DC: National Academy Press, 1985. 10. Kogan MD, Martin JA, Alexander GR, et al. The changing pattern of prenatal care utilization in the United States, 1981-1995, using different prenatal care indices. JAMA 1998;279:1623–1628. 11. Helfand M, Zimmer-Gembeck MJ. Practice variation and the risk of low birth weight in a public prenatal care program. Med Care 1997;35:16–31. 12. Greene MF. Two hundred years of progress in the practice of midwifery. N Engl J Med 2012;367:1732–1740. 13. Picklesimer AH, Billings D, Hale N, et al. The effect of CenteringPregnancy group prenatal care on preterm birth in a low-income population. Am J Obstet Gynecol 2012;206:415. e1–415.e7. 14. Ickovics JR, Kershaw TS, Westdahl C, et al. Group prenatal care and perinatal outcomes: A randomized controlled trial. Obstet Gynecol 2007;110:330–338. 15. Centering Healthcare Institute. A Better Way To Get Care. Accessed December 9, 2012. Available at: www.centeringhealthcare.org. 16. McClintock MK. Menstrual synchrony and suppression. Nature 1971;229:244–245. 17. Warren STH. Human pheromones: Have they been demonstrated? Behav Ecol Sociobiol 2003;54:89–97. 18. Shi L, Stevens GD, Wulu JT, et al. America’s health centers: Reducing racial and ethnic disparities in prenatal care and birth outcomes. Health Serv Res 2004;39:1881–1902. 19. Kotelchuck M, Kogan MD, Alexander GR. The influence of site of care on the content of prenatal care for low income women. Matern Child Health J 1;1997:25–34. 20. Hollowell J, Oakley L, Kurinczuk JJ, et al. The effectiveness of antenatal care programmes to reduce infant mortality and preterm birth in socially disadvantaged and vulnerable women in highincome countries: A systematic review. BMC Pregnancy Childbirth 2011;11:13. doi:10.1186/1471-2393-11-13. 21. Olds DL, Robinson J, Pettitt L, et al. Effects of home visits by paraprofessionals and by nurses: Age 4 follow-up results of a randomized trial. Pediatrics 2004;114:1560–1568.
BIRTH 40:1 March 2013
IN THE LITERATURE COMMENTARY ON: Picklesimer AH, Billings D, Hale N, Blackhurst D, Covington-Kolb S. The effect of CenteringPregnancy group prenatal care on preterm birth in a low-income population. Am J Obstet Gynecol 2012;206:415.e1–415.e7.
Does the CenteringPregnancy Group Prenatal Care Program Reduce Preterm Birth? The Conclusions Are Premature Neal F. Devitt, MD, FAAFP ABSTRACT: Prenatal care is promoted as a means to a healthy pregnancy outcome. In the United States great resources have been spent to expand the availability of a program of prenatal care, but without evidence for its effectiveness in the general population. Despite greater access to prenatal care over the last several decades, there has been no improvement in obstetric outcomes, such as preterm delivery. The CenteringPregnancy program of group prenatal visits is a novel form of prenatal care that, according to several studies, has been said to improve satisfaction with prenatal visits and with pregnancy outcomes. A careful reading of the studies shows that those goals are yet to be achieved. Innovation is welcome and essential, but larger studies are needed to achieve statistical significance to demonstrate improved outcome. (BIRTH 40:1 March 2013)
Key words: prenatal care, group prenatal care, CenteringPregnancy, pregnancy The United States appears to be emerging from the midst of a preterm birth epidemic (1). The preterm birth rate rose by more than one-third from 1981 to 2006, and although at its lowest level in more than a decade, the 2011 rate is still higher than rates reported during the 1980s and most of the 1990s. In 2011 more than 1 in 10 babies were born preterm. All practitioners and policymakers would agree that this preterm birth rate is too high and is a public health crisis. The cost of medical care for babies born significantly preterm is much greater than that for babies born at term, and the Neal F. Devitt is Senior Physician at the La Familia Medical Center, a Community Health Center, and Faculty member at The Northern New Mexico Family Medicine Residency, Santa Fe, New Mexico, U.S.A. Address correspondence to Neal Devitt, MD, La Familia Medical Center, 1035 Alto Street, Santa Fe, New Mexico 87505, USA.
© 2013, Copyright the Authors Journal compilation © 2013, Wiley Periodicals, Inc.
physical and intellectual disabilities that many of them carry on to adulthood are a great burden to the child, the family, and society. Prenatal care is promoted as a means to a healthy pregnancy outcome. However, to this day there is no evidence that prenatal care, as it is currently structured, is effective in improving the health of the childbearing population and the outcome of their pregnancies (2,3). Prenatal care is a relatively modern concept, first developed in the British Isles in the late 1800s and imported into the United States in 1908 (4). It was promoted by J.W. Williams (5) in his seminal 1914 JAMA article, “The Limitations and Possibilities of Prenatal Care,” as a means to identify and possibly treat complications of pregnancy, such as eclampsia and syphilis. At that time the physician did little more prenatally than monitor blood pressure and proteinuria. Much of what we consider to be prenatal care was delivered in the home of the expectant mother by public health nurses. J.W. Williams’ prenatal instructions comprise
68 one page of his text (5). The pregnant woman is asked to send to his office a urine sample monthly for the first 7 months then biweekly for the remainder of her pregnancy. She is to call for bleeding and for signs of preeclampsia, but otherwise call the public health nurse at the beginning of labor and “let her use her judgment in sending for me.” (6, p 210). In the 1920s, the federal Children’s Bureau (7) first tried to standardize content of prenatal care (measurement of blood pressure, proteinuria, weight, and fundal height), using a form that may be still familiar to “more seasoned” physicians and midwives. In the 1930s and 1940s, physician groups campaigned to move the site of prenatal care from the domain of the public nurse in the family home to the physician in his office. Once established in the physician office, prenatal care exhibited little change from the 1940s to recent years. In the 1970s regionalization of perinatal care was promoted. In the 1980s two reports by the United States government, Caring for Our Future (8) and Preventing Low Birth-Weight (9) provided the impetus for increased funding of the federal Medicaid program for low-income women. The number of pregnant women covered by Medicaid rose from 17 percent in 1985 to 35 percent in 1998. However, no evaluation of its effectiveness or promulgation of any more effective models was conducted. Thus, Kogan et al concluded that, between 1981 and 1995, the use of prenatal care increased without any improvement in rates of preterm birth and low birthweight (10). Indeed, “too much” prenatal care may worsen outcomes (11). A recent review, “Two Hundred Years of Progress in the Practice of Midwifery,” focused mainly on the adoption of new technology without mentioning Williams’ efforts to develop and promote prenatal care, perhaps because it was published not in the Journal of the American Medical Association but in a competing journal (12). It is in this context that the paper “The effect of CenteringPregnancy group prenatal care on preterm birth in a low-income population”(13) is important. Picklesimer et al expand on the work by Ickovics et al (14), evaluating the CenteringPregnancy model of prenatal care. “Centering is a model of group health care that is changing how people think about their care. The model has three components: health assessment, education, and support, provided in a group facilitated by a health care provider” (15). This proprietary program uses group prenatal visits in which “Eight to twelve women with similar gestational ages meet together, learning care skills, participating in a facilitated discussion, and developing a support network with other group members. Each Pregnancy group meets for a total of 10 sessions throughout pregnancy and early postpartum. The practitioner, within the group space, completes standard physical health assessments” (15).
BIRTH 40:1 March 2013
Ickovics et al (14) and Picklesimer et al (13) are to be commended for putting forth a different model for prenatal care, and actually evaluating its effects on pregnancy outcome. However, I have several concerns about the program and the paper by Picklesimer et al. In their introduction as rationale for their study, the authors (13) reference Ickovics et al’s previous study (14), writing “the rate of preterm birth among women in group care was 33% lower than the rate of preterm birth for women in the traditional prenatal care control group.” This claimed benefit of CenteringPregnancy group visits needs further evaluation. Ickovics et al evaluated both clinical (preterm birth), process (number of prenatal visits) and nonclinical (patient knowledge and satisfaction) outcomes (14). I shall focus largely on the clinical outcomes. Comparing 623 women randomized to group care with 370 women in traditional care, they found no significant difference in gestational age (reported by week), low birthweight, mean birthweight, neonatal intensive care unit admission, or total cost of prenatal care (available for only one of the two study sites). The claimed reduction in preterm birth was only a reduction in births before 37 completed weeks (i.e., before 259 days). There are important differences between the earlier study of Ickovics et al (14) and the paper by Picklesimer et al (13). In the study of Ickovics et al (14) the population was 80 percent black, whereas the population studied by Picklesimer et al (13) was about onethird black, one-third non-Hispanic white, one-sixth white Hispanic, and one-sixth other, giving the results more generalizability. Weaknesses are the study’s retrospective design and the self-selection of the intervention group. In addition, data were collected from electronic birth certificate database worksheets, which, according to the authors, “do not include information about the presence or absence of many of the high-risk conditions that would have excluded women from participation in our group prenatal care program such as maternal cardiac or renal disease” (13). In addition, fewer of the nulliparous women in group care used tobacco, and 15 percent of the study group withdrew from group visits. These caveats aside, again the CenteringPregnancy program is said to have reduced preterm births by 47 percent. The percentage of very preterm births (less than 32 weeks of gestation) was also reduced, but without significant improvements in actual clinical outcome. Mean birthweight was larger by 67 g, but no significant difference was observed in low birthweight (less than 2,500 g) or in neonatal intensive care unit admission. It is also important to realize that both these studies included more than one intervention. The CenteringPregnancy curriculum is one intervention and group care is another intervention, but they are lumped together. We
69
BIRTH 40:1 March 2013
do not know whether beneficial effects resulted from the curriculum or simply from some independent effect of group visits. Although unlikely, a beneficial effect on pregnancy outcome as a result of a pheromone effect of group proximity cannot be completely excluded (e.g., similar to McClintock’s description of menstrual synchrony in a women’s college dormitory (16,17). More likely, women in a group could share resources and strategies that could have a positive effect on pregnancy outcome independent of any curriculum. Analogously, prenatal clients of community health centers, despite their poverty, have a lower percentage of low birthweight babies than the United States population as a whole (18). This outcome is thought to be the result of the broad array of social resources available through community health centers (19). I have not addressed the nonclinical outcomes, which are substantial. The stated increase in patient knowledge and satisfaction has the potential to improve the outcome of future pregnancies. I would look forward to a study evaluating the outcome of future pregnancies in women in this study group who receive the usual prenatal care in a subsequent pregnancy compared with a control group who never received group care to evaluate whether these benefits are sustained. The interested reader may refer to Hollowell et al (20) for a review of the effectiveness of other interventions in prenatal care. Although, not traditionally considered to be prenatal care, a program of antenatal and postnatal home visits with a set curriculum developed by Olds et al was shown to reduce rates of low birthweight (21). CenteringPregnancy may indeed be able to lower the preterm birth rate. The small size of these studies is another limitation—a limitation that may preclude statistical significance. Too many studies published in the obstetric literature include substantially fewer than 1,000 women, a size that is unlikely to demonstrate benefit from an intervention in the United States, given the relatively low frequency of many obstetric complications. Major studies of treatments of cancer or cardiovascular disease routinely include tens of thousands of patients and multiple academic centers, and often span continents. When we study effective programs for maternity care, we are investing in our future. Large studies are costly. It is not enough to critique studies for being too small. We must also ask why we do not have the resources for larger studies. The average age of a U.S. Senator is 62 years and the average age of a Representative is 57 years. Eighty-three percent of our Congresspeople are white and 83 percent are male. These are the people who are more motivated to fund studies of cancer and cardiac disease. To improve research on effective prenatal care, perhaps we need to elect more women of reproductive age to Congress.
References 1. Hamilton BE, Martin JA, Ventura SJ. Births: Preliminary data for 2011. Natl Vital Stat Rep 2012;61(5):5–6. 2. Krans EE, Davis MM. Preventing Low Birthweight: 25 years prenatal risk, and the failure to reinvent prenatal care. Am J Obstet Gynecol 2012;206:398–403. 3. Alexander GR, Kotelchuck M. Assessing the role and effectiveness of prenatal care: history, challenges, and directions for future research. Public Health Rep 2001;116:306–316. 4. West M. The growth of prenatal work in this country. Trans Am Assoc Study Prevention Infant Mortal 1914;5:69–108. 5. Williams JW. The limitations and possibilities of prenatal care. JAMA 1915;64:95–101. 6. Williams JW. Obstetrics. New York and London: D Appleton and Co, 1912. 7. De Normandie RL. Standards of Prenatal Care: An Outline for the Use of Physicians. Publication No. 153:9-10. Washington, DC: Children’s Bureau, 1925. 8. Rosen MG, Culpepper L, Goldenberg R, et al. Caring for Our Future: The Content of Prenatal Care. A Report of the Public Health Service Expert Panel on the Content of Prenatal Care. NIH Publication No. 90-3182. Washington, DC: U.S. Department of Health and Human Services, 1989. 9. Institute of Medicine. Preventing Low Birth-Weight. Washington DC: National Academy Press, 1985. 10. Kogan MD, Martin JA, Alexander GR, et al. The changing pattern of prenatal care utilization in the United States, 1981-1995, using different prenatal care indices. JAMA 1998;279:1623–1628. 11. Helfand M, Zimmer-Gembeck MJ. Practice variation and the risk of low birth weight in a public prenatal care program. Med Care 1997;35:16–31. 12. Greene MF. Two hundred years of progress in the practice of midwifery. N Engl J Med 2012;367:1732–1740. 13. Picklesimer AH, Billings D, Hale N, et al. The effect of CenteringPregnancy group prenatal care on preterm birth in a low-income population. Am J Obstet Gynecol 2012;206:415. e1–415.e7. 14. Ickovics JR, Kershaw TS, Westdahl C, et al. Group prenatal care and perinatal outcomes: A randomized controlled trial. Obstet Gynecol 2007;110:330–338. 15. Centering Healthcare Institute. A Better Way To Get Care. Accessed December 9, 2012. Available at: www.centeringhealthcare.org. 16. McClintock MK. Menstrual synchrony and suppression. Nature 1971;229:244–245. 17. Warren STH. Human pheromones: Have they been demonstrated? Behav Ecol Sociobiol 2003;54:89–97. 18. Shi L, Stevens GD, Wulu JT, et al. America’s health centers: Reducing racial and ethnic disparities in prenatal care and birth outcomes. Health Serv Res 2004;39:1881–1902. 19. Kotelchuck M, Kogan MD, Alexander GR. The influence of site of care on the content of prenatal care for low income women. Matern Child Health J 1;1997:25–34. 20. Hollowell J, Oakley L, Kurinczuk JJ, et al. The effectiveness of antenatal care programmes to reduce infant mortality and preterm birth in socially disadvantaged and vulnerable women in highincome countries: A systematic review. BMC Pregnancy Childbirth 2011;11:13. doi:10.1186/1471-2393-11-13. 21. Olds DL, Robinson J, Pettitt L, et al. Effects of home visits by paraprofessionals and by nurses: Age 4 follow-up results of a randomized trial. Pediatrics 2004;114:1560–1568.
