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Characterizing risk profiles of infants who are delivered at late preterm gestations: does it matter?
Editorials
www.AJOG.org
Characterizing risk profiles of infants who are delivered at late preterm gestations: does it matter? Cande V. Ananth, PhD, MPH; Cynthia Gyamfi, MD; Lucky Jain, MD, MBA
P
reterm birth has to be one of the most highly studied complications in contemporary obstetrics, yet we have progressed little toward understanding its cause. Preterm birth (PTB; delivery at ⬍ 37 weeks of gestation) affected roughly 525,000 births (12.8% of all births) in the United States in 2006.1 Despite efforts to prevent PTB, the rate has shown a steady temporal increase in most industrialized countries,2-6 largely after a concurrent increase in medically indicated PTBs.2,7 In fact, the increase in indicated PTBs has been the subject of recent debate,8,9 with the largest proportion of obstetric interventions occurring at 34 weeks 1 day to 36 weeks 6 days of gestation,10,11 which is a gestational age window that is now termed late preterm births.12 The increase in indicated PTBs is associated with a substantially large and favorable decline in stillbirth and neonatal mortality rates,2,8 which suggests that obstetric interventions at preterm gestational ages may be beneficial insofar as perinatal death is concerned. In fact, the sharp temporal decline in stillbirths and infant deaths in the United States (1990-2004)13 has occurred despite an accompanying temporal increase in both PTBs overall (ie, ⬍ 37 weeks of gestation) and the late preterm gestations (Figure). Accumulating data suggest that singleton infants who are born at late preterm gestations are at increased risk for perinatal death, when compared with infants who are born at term. In addition, infants who are delivered at late preterm gestations have substantially higher risks of transient tachypnea, respiratory distress, hypoglycemia, pulmonary hypertension, and related complications than do those infants who are born at term.9,14-18 A recent cohort study of infants who were born at the late preterm gestation who were followed to the fifth grade revealed poorer school performance than infants who were delivered at term.19 A large population-based cohort study from Norway20 reported increased risks of cerebral palsy (relative risk [RR], 2.7; 95% confidence interval [CI], 2.2-3.3), mental retardation (RR, 1.6; 95% CI, 1.4-1.8), schizophrenia (RR,1.6; 95% CI, 1.4-1.8), and other disorders of psychologic developFrom the Division of Epidemiology and Biostatistics, Department of Obstetrics, Gynecology, and Reproductive Sciences (Dr Ananth), UMDNJ-Robert Wood Johnson Medical School, New Brunswick, NJ; Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology (Dr Gyamfi), Columbia University, New York, NY; Department of Pediatrics (Dr Jain), Emory University School of Medicine, Atlanta, GA. 0002-9378/free © 2008 Mosby, Inc. All rights reserved. doi: 10.1016/j.ajog.2008.08.040
See related articles, pages 367 and 370
ment, behavior, and emotion (RR, 1.5; 95% CI, 1.2-1.8) among late preterm infants in comparison with their term counterparts. Not only are infants who are born at late preterm gestations at increased risks of developmental, social, and neurocognitive deficits, but these infants also are at 40% increased risk (RR, 1.4; 95% CI, 1.3-1.5) for any medical disability, which severely affects working capacity later in adulthood.20 Two interesting articles in this issue of the American Journal of Obstetrics and Gynecology provide important insights regarding outcomes of infants who are delivered at the late preterm gestations. Based on data on women at impending risk for spontaneous preterm labor who delivered at ⱖ 32 weeks of gestation (n ⫽ 264), Bastek et al21 report that a little over onefourth of infants were delivered at the late preterm gestation. Their data showed higher risk of combined acute neonatal morbidities that lead to increased lengths of neonatal intensive care unit stay and of the use of health care resources during the neonatal period in infants who were delivered at late preterm gestations. In addition, their data also showed increased risks of long-term morbidities, persistent need for health care resources beyond the neonatal period, and indicators for neurodevelopmental complication in the late preterm gestations in comparison with infants who were born at term. The authors report that, for infants who were delivered at 34 weeks to 34 weeks 6 days of gestation, the risk for adverse outcomes was no different from infants who were delivered at 32 weeks to 33 weeks 6 days of gestation. These findings fly in the face of conventional wisdom that gestational week 34 marks a physiologic watershed zone in fetal maturity. Such a belief is ingrained in the current standard of care, which calls for withholding tocolytics and antenatal steroids in women with signs and symptoms of preterm labor at or beyond 34 weeks of gestation and augmentation of labor for preterm premature rupture of membranes; it also forms the basis for medically indicated PTBs. However, the 23% decrease in adverse neonatal outcomes with each advancing week of gestation between 32 and 39 weeks underscores the need for a closer look at current obstetric practices. A second study by Cheng et al22 suggests that the problem of neonatal morbidity extends beyond the late preterm period. They reviewed ⬎ 2 million pregnancies in the United States to evaluate whether increasing gestational age in term pregnancies is associated with a decrease in perinatal complications. Using 39 weeks of gestation as a reference point, they found that the risk of respiratory morbidity was significantly higher at 37 (odds ratio, 3.12; 95% CI, 2.90-3.38) and 38 weeks of gestation (odds ratio, 1.30; 95% CI, 1.19-1.43). These infants were, however, at lower risk for meconium aspiration. Additionally, delivery at 40 or 41 weeks of gestation was associated with a OCTOBER 2008 American Journal of Obstetrics & Gynecology
329
Editorials
www.AJOG.org
FIGURE
Trends in late preterm birth, stillbirth, and infant mortality, United States, 1990-2004 10
Infant deaths
9
9
Stillbirths and
Late preterm births 8
8
7
7 Stillbirths
6
6 0
infant deaths per 1000 births
Percent of late preterm births (34-36 weeks)
10
1990
1995
2000
2005
0
Year
The left axis shows trends in stillbirth and infant mortality rates; the right axis shows trends in late preterm births (34-36 wks). Late preterm birth rates are shown per 100 live births; stillbirth rates, per 1000 total births; and infant death rates, per 1000 live births. (Source: Linked birth and infant death data, National Center for Health Statistics.)
higher risk of neonatal injury and meconium aspiration. These findings further validate the recommendations of the American College of Obstetricians and Gynecologists that elective labor induction or cesarean delivery should not be performed before 39 weeks of gestation.23 Taken together, these 2 articles22,23 and previous bodies of research on late PTB underscore the acute need to better characterize risks of short- and long-term morbidity to infants who are delivered at these gestations. As previously opined, longitudinal studies that entail close monitoring and long-term follow-up of those infants who were delivered at late preterm gestations are necessary to understand the burden of risks these newborn infants are likely to face during infancy and beyond.24 More importantly, the maternal and fetal indications that necessitate obstetric interventions at these gestations (which include preeclampsia, intrauterine growth restriction, and placental abruption that together constitute the syndrome of “ischemic placental disease”8,25) need careful study. Although the risk profiles for infants who are delivered at late preterm gestations are relatively better than those infants who are delivered at earlier gestations, they nevertheless constitute a highrisk group. The concerns for adverse neonatal outcome notwithstanding, the remarkable reduction in perinatal mortality rates that have been realized in recent years cannot be ignored. It has been proposed that, if all women who progress to term gestation were delivered at 39 weeks of gestation, it would prevent 6000 stillbirths in the United States alone, which is a gain that, by any measure of success, far exceeds that from any other intervention to date.26 However, such gains surely will be ac330
American Journal of Obstetrics & Gynecology OCTOBER 2008
companied by an escalation of neonatal intensive care unit admissions and complications, with untold short- and long-term complications.27 In retrospect, the staggering statistics on PTBs in general and the late preterm gestation in particular continue to constitute a vulnerable population of “at-risk” infants. Efforts to understand both short- and long-term risks to infants who are delivered in the late preterm gestation must include simultaneous and intense monitoring of the perinatal mortality and morbidity rates as efforts to address the late PTB going forward. The heterogeneity in risk profiles of adverse perinatal outcomes by gestational age at delivery provides strong impetus that future research should move away from associating the gestational age at delivery, per se, to adverse outcomes, but should focus on the indication(s) for early delivery (ie, the underlying pathophysiologic process that leads to elective or spontaneous pref term delivery). REFERENCES 1. Hamilton BE, Martin JA, Ventura SJ. Births: preliminary data for 2006. Natl Vital Stat Rep 2007;56:1-18. 2. Ananth CV, Joseph KS, Oyelese Y, Demissie K, Vintzileos AM. Trends in preterm birth and perinatal mortality among singletons: United States, 1989 through 2000. Obstet Gynecol 2005;105:1084-91. 3. Ananth CV, Vintzileos AM. Epidemiology of preterm birth and its clinical subtypes. J Matern Fetal Neonatal Med 2006;19:773-82. 4. Bettegowda VR, Dias T, Davidoff MJ, Damus K, Callaghan WM, Petrini JR. The relationship between cesarean delivery and gestational age among US singleton births. Clin Perinatol 2008;35:309-23. 5. Joseph KS, Kramer MS, Marcoux S, et al. Determinants of preterm birth rates in Canada from 1981 through 1983 and from 1992 through 1994. N Engl J Med 1998;339:1434-9. 6. Kramer MS, Platt R, Yang H, et al. Secular trends in preterm birth: a hospital-based cohort study. JAMA 1998;280:1849-54. 7. Ananth CV, Joseph KS, Demissie K, Vintzileos AM. Trends in twin preterm birth subtypes in the United States, 1989 through 2000: impact on perinatal mortality. Am J Obstet Gynecol 2005;193:1076-82. 8. Ananth CV, Vintzileos AM. Medically indicated preterm birth: recognizing the importance of the problem. Clin Perinatol 2008;35:53-67. 9. Fuchs K, Gyamfi C. The influence of obstetric practices on late prematurity. Clin Perinatol 2008;35:343-60. 10. Davidoff MJ, Dias T, Damus K, et al. Changes in the gestational age distribution among US singleton births: impact on rates of late preterm birth, 1992 to 2002. Semin Perinatol 2006;30:8-15. 11. Joseph KS, Demissie K, Kramer MS. Obstetric intervention, stillbirth, and preterm birth. Semin Perinatol 2002;26:250-9. 12. Raju TN. Optimizing care and outcome for late-preterm (near-term) infants: a summary of the workshop sponsored by the National Institute of Child Health and Human Development. Pediatrics 2006;118:1207-14. 13. MacDorman MF, Munson ML, Kirmeyer S. Fetal and perinatal mortality, United States, 2004. Natl Vital Stat Rep 2007;56:1-19. 14. Engle WA, Tomashek KM, Wallman C. “Late-preterm” infants: a population at risk. Pediatrics 2007;120:1390-401. 15. Engle WA, Kominiarek MA. Late preterm infants, early term infants, and timing of elective deliveries. Clin Perinatol 2008;35:325-41. 16. McIntire DD, Leveno KJ. Neonatal mortality and morbidity rates in late preterm births compared with births at term. Obstet Gynecol 2008;111:35-41. 17. Shapiro-Mendoza CK, Tomashek KM, Kotelchuck M, et al. Effect of late-preterm birth and maternal medical conditions on newborn morbidity risk. Pediatrics 2008;121:e223-32.
www.AJOG.org 18. Tomashek KM, Shapiro-Mendoza CK, Davidoff MJ, Petrini JR. Differences in mortality between late-preterm and term singleton infants in the United States, 1995-2002. J Pediatr 2007;151:450-6. 19. Chyi LJ, Lee HC, Hintz SR, Gould JB, Sutcliffe TL. School outcomes of late preterm infants: special needs and challenges for infants born at 32 to 36 weeks gestation. J Pediatr 2008;153:25-31. 20. Moster D, Lie RT, Markestad T. Long-term medical and social consequences of preterm birth. N Engl J Med 2008;359:262-73. 21. Bastek JA, Sammel MD, Paré E, Srinivas SK, Posencheg MA, Elovitz MA. Adverse neonatal outcomes: examining the risks between preterm, late preterm, and term infants. Am J Obstet Gynecol 2008;199:367.e1-8. 22. Cheng YW, Nicholson JM, Nakagwa S, Bruckner TA, Washington E, Caughey AB. Perinatal outcomes in low-risk, term pregnancies: do they differ by week of gestation? Am J Obstet Gynecol 2008;199:370.e1-7.
Editorials 23. American College of Obstetricians and Gynecologists. Practice bulletin No.: 10: induction of labor. Washington (DC): The College; 1999. 24. Jain L. School outcome in late preterm infants: a cause for concern. J Pediatr 2008;153:5-6. 25. Ananth CV, Vintzileos AM. Maternal-fetal conditions necessitating a medical intervention resulting in preterm birth. Am J Obstet Gynecol 2006;195:1557-63. 26. Hankins GD, Clark SM, Munn MB. Cesarean section on request at 39 weeks: impact on shoulder dystocia, fetal trauma, neonatal encephalopathy, and intrauterine fetal demise. Semin Perinatol 2006;30:276-87. 27. Yoder BA, Gordon MC, Barth WH Jr. Late-preterm birth: does the changing obstetric paradigm alter the epidemiology of respiratory complications? Obstet Gynecol 2008;111:814-22.
OCTOBER 2008 American Journal of Obstetrics & Gynecology
331
www.AJOG.org
Characterizing risk profiles of infants who are delivered at late preterm gestations: does it matter? Cande V. Ananth, PhD, MPH; Cynthia Gyamfi, MD; Lucky Jain, MD, MBA
P
reterm birth has to be one of the most highly studied complications in contemporary obstetrics, yet we have progressed little toward understanding its cause. Preterm birth (PTB; delivery at ⬍ 37 weeks of gestation) affected roughly 525,000 births (12.8% of all births) in the United States in 2006.1 Despite efforts to prevent PTB, the rate has shown a steady temporal increase in most industrialized countries,2-6 largely after a concurrent increase in medically indicated PTBs.2,7 In fact, the increase in indicated PTBs has been the subject of recent debate,8,9 with the largest proportion of obstetric interventions occurring at 34 weeks 1 day to 36 weeks 6 days of gestation,10,11 which is a gestational age window that is now termed late preterm births.12 The increase in indicated PTBs is associated with a substantially large and favorable decline in stillbirth and neonatal mortality rates,2,8 which suggests that obstetric interventions at preterm gestational ages may be beneficial insofar as perinatal death is concerned. In fact, the sharp temporal decline in stillbirths and infant deaths in the United States (1990-2004)13 has occurred despite an accompanying temporal increase in both PTBs overall (ie, ⬍ 37 weeks of gestation) and the late preterm gestations (Figure). Accumulating data suggest that singleton infants who are born at late preterm gestations are at increased risk for perinatal death, when compared with infants who are born at term. In addition, infants who are delivered at late preterm gestations have substantially higher risks of transient tachypnea, respiratory distress, hypoglycemia, pulmonary hypertension, and related complications than do those infants who are born at term.9,14-18 A recent cohort study of infants who were born at the late preterm gestation who were followed to the fifth grade revealed poorer school performance than infants who were delivered at term.19 A large population-based cohort study from Norway20 reported increased risks of cerebral palsy (relative risk [RR], 2.7; 95% confidence interval [CI], 2.2-3.3), mental retardation (RR, 1.6; 95% CI, 1.4-1.8), schizophrenia (RR,1.6; 95% CI, 1.4-1.8), and other disorders of psychologic developFrom the Division of Epidemiology and Biostatistics, Department of Obstetrics, Gynecology, and Reproductive Sciences (Dr Ananth), UMDNJ-Robert Wood Johnson Medical School, New Brunswick, NJ; Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology (Dr Gyamfi), Columbia University, New York, NY; Department of Pediatrics (Dr Jain), Emory University School of Medicine, Atlanta, GA. 0002-9378/free © 2008 Mosby, Inc. All rights reserved. doi: 10.1016/j.ajog.2008.08.040
See related articles, pages 367 and 370
ment, behavior, and emotion (RR, 1.5; 95% CI, 1.2-1.8) among late preterm infants in comparison with their term counterparts. Not only are infants who are born at late preterm gestations at increased risks of developmental, social, and neurocognitive deficits, but these infants also are at 40% increased risk (RR, 1.4; 95% CI, 1.3-1.5) for any medical disability, which severely affects working capacity later in adulthood.20 Two interesting articles in this issue of the American Journal of Obstetrics and Gynecology provide important insights regarding outcomes of infants who are delivered at the late preterm gestations. Based on data on women at impending risk for spontaneous preterm labor who delivered at ⱖ 32 weeks of gestation (n ⫽ 264), Bastek et al21 report that a little over onefourth of infants were delivered at the late preterm gestation. Their data showed higher risk of combined acute neonatal morbidities that lead to increased lengths of neonatal intensive care unit stay and of the use of health care resources during the neonatal period in infants who were delivered at late preterm gestations. In addition, their data also showed increased risks of long-term morbidities, persistent need for health care resources beyond the neonatal period, and indicators for neurodevelopmental complication in the late preterm gestations in comparison with infants who were born at term. The authors report that, for infants who were delivered at 34 weeks to 34 weeks 6 days of gestation, the risk for adverse outcomes was no different from infants who were delivered at 32 weeks to 33 weeks 6 days of gestation. These findings fly in the face of conventional wisdom that gestational week 34 marks a physiologic watershed zone in fetal maturity. Such a belief is ingrained in the current standard of care, which calls for withholding tocolytics and antenatal steroids in women with signs and symptoms of preterm labor at or beyond 34 weeks of gestation and augmentation of labor for preterm premature rupture of membranes; it also forms the basis for medically indicated PTBs. However, the 23% decrease in adverse neonatal outcomes with each advancing week of gestation between 32 and 39 weeks underscores the need for a closer look at current obstetric practices. A second study by Cheng et al22 suggests that the problem of neonatal morbidity extends beyond the late preterm period. They reviewed ⬎ 2 million pregnancies in the United States to evaluate whether increasing gestational age in term pregnancies is associated with a decrease in perinatal complications. Using 39 weeks of gestation as a reference point, they found that the risk of respiratory morbidity was significantly higher at 37 (odds ratio, 3.12; 95% CI, 2.90-3.38) and 38 weeks of gestation (odds ratio, 1.30; 95% CI, 1.19-1.43). These infants were, however, at lower risk for meconium aspiration. Additionally, delivery at 40 or 41 weeks of gestation was associated with a OCTOBER 2008 American Journal of Obstetrics & Gynecology
329
Editorials
www.AJOG.org
FIGURE
Trends in late preterm birth, stillbirth, and infant mortality, United States, 1990-2004 10
Infant deaths
9
9
Stillbirths and
Late preterm births 8
8
7
7 Stillbirths
6
6 0
infant deaths per 1000 births
Percent of late preterm births (34-36 weeks)
10
1990
1995
2000
2005
0
Year
The left axis shows trends in stillbirth and infant mortality rates; the right axis shows trends in late preterm births (34-36 wks). Late preterm birth rates are shown per 100 live births; stillbirth rates, per 1000 total births; and infant death rates, per 1000 live births. (Source: Linked birth and infant death data, National Center for Health Statistics.)
higher risk of neonatal injury and meconium aspiration. These findings further validate the recommendations of the American College of Obstetricians and Gynecologists that elective labor induction or cesarean delivery should not be performed before 39 weeks of gestation.23 Taken together, these 2 articles22,23 and previous bodies of research on late PTB underscore the acute need to better characterize risks of short- and long-term morbidity to infants who are delivered at these gestations. As previously opined, longitudinal studies that entail close monitoring and long-term follow-up of those infants who were delivered at late preterm gestations are necessary to understand the burden of risks these newborn infants are likely to face during infancy and beyond.24 More importantly, the maternal and fetal indications that necessitate obstetric interventions at these gestations (which include preeclampsia, intrauterine growth restriction, and placental abruption that together constitute the syndrome of “ischemic placental disease”8,25) need careful study. Although the risk profiles for infants who are delivered at late preterm gestations are relatively better than those infants who are delivered at earlier gestations, they nevertheless constitute a highrisk group. The concerns for adverse neonatal outcome notwithstanding, the remarkable reduction in perinatal mortality rates that have been realized in recent years cannot be ignored. It has been proposed that, if all women who progress to term gestation were delivered at 39 weeks of gestation, it would prevent 6000 stillbirths in the United States alone, which is a gain that, by any measure of success, far exceeds that from any other intervention to date.26 However, such gains surely will be ac330
American Journal of Obstetrics & Gynecology OCTOBER 2008
companied by an escalation of neonatal intensive care unit admissions and complications, with untold short- and long-term complications.27 In retrospect, the staggering statistics on PTBs in general and the late preterm gestation in particular continue to constitute a vulnerable population of “at-risk” infants. Efforts to understand both short- and long-term risks to infants who are delivered in the late preterm gestation must include simultaneous and intense monitoring of the perinatal mortality and morbidity rates as efforts to address the late PTB going forward. The heterogeneity in risk profiles of adverse perinatal outcomes by gestational age at delivery provides strong impetus that future research should move away from associating the gestational age at delivery, per se, to adverse outcomes, but should focus on the indication(s) for early delivery (ie, the underlying pathophysiologic process that leads to elective or spontaneous pref term delivery). REFERENCES 1. Hamilton BE, Martin JA, Ventura SJ. Births: preliminary data for 2006. Natl Vital Stat Rep 2007;56:1-18. 2. Ananth CV, Joseph KS, Oyelese Y, Demissie K, Vintzileos AM. Trends in preterm birth and perinatal mortality among singletons: United States, 1989 through 2000. Obstet Gynecol 2005;105:1084-91. 3. Ananth CV, Vintzileos AM. Epidemiology of preterm birth and its clinical subtypes. J Matern Fetal Neonatal Med 2006;19:773-82. 4. Bettegowda VR, Dias T, Davidoff MJ, Damus K, Callaghan WM, Petrini JR. The relationship between cesarean delivery and gestational age among US singleton births. Clin Perinatol 2008;35:309-23. 5. Joseph KS, Kramer MS, Marcoux S, et al. Determinants of preterm birth rates in Canada from 1981 through 1983 and from 1992 through 1994. N Engl J Med 1998;339:1434-9. 6. Kramer MS, Platt R, Yang H, et al. Secular trends in preterm birth: a hospital-based cohort study. JAMA 1998;280:1849-54. 7. Ananth CV, Joseph KS, Demissie K, Vintzileos AM. Trends in twin preterm birth subtypes in the United States, 1989 through 2000: impact on perinatal mortality. Am J Obstet Gynecol 2005;193:1076-82. 8. Ananth CV, Vintzileos AM. Medically indicated preterm birth: recognizing the importance of the problem. Clin Perinatol 2008;35:53-67. 9. Fuchs K, Gyamfi C. The influence of obstetric practices on late prematurity. Clin Perinatol 2008;35:343-60. 10. Davidoff MJ, Dias T, Damus K, et al. Changes in the gestational age distribution among US singleton births: impact on rates of late preterm birth, 1992 to 2002. Semin Perinatol 2006;30:8-15. 11. Joseph KS, Demissie K, Kramer MS. Obstetric intervention, stillbirth, and preterm birth. Semin Perinatol 2002;26:250-9. 12. Raju TN. Optimizing care and outcome for late-preterm (near-term) infants: a summary of the workshop sponsored by the National Institute of Child Health and Human Development. Pediatrics 2006;118:1207-14. 13. MacDorman MF, Munson ML, Kirmeyer S. Fetal and perinatal mortality, United States, 2004. Natl Vital Stat Rep 2007;56:1-19. 14. Engle WA, Tomashek KM, Wallman C. “Late-preterm” infants: a population at risk. Pediatrics 2007;120:1390-401. 15. Engle WA, Kominiarek MA. Late preterm infants, early term infants, and timing of elective deliveries. Clin Perinatol 2008;35:325-41. 16. McIntire DD, Leveno KJ. Neonatal mortality and morbidity rates in late preterm births compared with births at term. Obstet Gynecol 2008;111:35-41. 17. Shapiro-Mendoza CK, Tomashek KM, Kotelchuck M, et al. Effect of late-preterm birth and maternal medical conditions on newborn morbidity risk. Pediatrics 2008;121:e223-32.
www.AJOG.org 18. Tomashek KM, Shapiro-Mendoza CK, Davidoff MJ, Petrini JR. Differences in mortality between late-preterm and term singleton infants in the United States, 1995-2002. J Pediatr 2007;151:450-6. 19. Chyi LJ, Lee HC, Hintz SR, Gould JB, Sutcliffe TL. School outcomes of late preterm infants: special needs and challenges for infants born at 32 to 36 weeks gestation. J Pediatr 2008;153:25-31. 20. Moster D, Lie RT, Markestad T. Long-term medical and social consequences of preterm birth. N Engl J Med 2008;359:262-73. 21. Bastek JA, Sammel MD, Paré E, Srinivas SK, Posencheg MA, Elovitz MA. Adverse neonatal outcomes: examining the risks between preterm, late preterm, and term infants. Am J Obstet Gynecol 2008;199:367.e1-8. 22. Cheng YW, Nicholson JM, Nakagwa S, Bruckner TA, Washington E, Caughey AB. Perinatal outcomes in low-risk, term pregnancies: do they differ by week of gestation? Am J Obstet Gynecol 2008;199:370.e1-7.
Editorials 23. American College of Obstetricians and Gynecologists. Practice bulletin No.: 10: induction of labor. Washington (DC): The College; 1999. 24. Jain L. School outcome in late preterm infants: a cause for concern. J Pediatr 2008;153:5-6. 25. Ananth CV, Vintzileos AM. Maternal-fetal conditions necessitating a medical intervention resulting in preterm birth. Am J Obstet Gynecol 2006;195:1557-63. 26. Hankins GD, Clark SM, Munn MB. Cesarean section on request at 39 weeks: impact on shoulder dystocia, fetal trauma, neonatal encephalopathy, and intrauterine fetal demise. Semin Perinatol 2006;30:276-87. 27. Yoder BA, Gordon MC, Barth WH Jr. Late-preterm birth: does the changing obstetric paradigm alter the epidemiology of respiratory complications? Obstet Gynecol 2008;111:814-22.
OCTOBER 2008 American Journal of Obstetrics & Gynecology
331