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Late preterm births: irreducible because E = mc2
SMFM Debates
www. AJOG.org
The editors of the Journal and the SMFM Publication Committee are pleased to provide this summary of a debate conducted at the 31st annual meeting of the Society for Maternal–Fetal Medicine (The Pregnancy Meeting), San Francisco, CA, Feb. 7-12, 2011. One entry in this series will run every month from May through October 2011.
Late preterm birth: can it be reduced? THE ISSUE: Defined as delivery at 340/7-366/7weeks, late preterm births have increased by 15% between 1992 and 2002 and currently they
occur in about 8% of singletons and 35% of multiple gestations. Compared with newborns at 39 weeks, late preterm births undeniably have a significantly higher rate of morbidity (respiratory distress syndrome, pneumonia, need for ventilation), as well as neonatal and infant mortality. Thus, to lower the rate of late preterm birth seems to be self-evident necessity, but there is a need for judicious caution because there is insufficient evidence that prolonging these pregnancies improves maternal-fetal outcomes.
Cynthia Gyamfi Bannerman, MD Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Columbia University Medical Center, New York, NY
L
ate preterm delivery, defined as birth between 34 0/7 to 36 6/7 weeks’ gestation, has increased at a rate higher than that of all preterm birth for the past 20 years.1,2 It has contributed to the shift in the average gestational age at birth from 40 weeks to 39 weeks, and it is driving the increase in prematurity. Each state has seen an increase in late preterm birth, and the increasing incidence has been noted in both singleton and multiple pregnancies.3 The morbidity associated with late preterm birth has been the focus of recent literature, and the importance of these findings must be underscored. Late preterm birth is associated with increased respiratory morbidities, including respiratory distress syndrome, transient tachypnea of the newborn, and the need for ventilatory support.4 It has also been associated with intraventricular hemorrhage, necrotizing enterocolitis, sepsis, hyperbilirubinemia, and feeding difficulties.4,5 Unfortunately, mortality is also increased in this group. Late preterm infants are at a 3- to 6-fold increased risk of death than their term counterparts.1 The morbidity and mortality associated with late preterm birth makes reduction of this phenomenon a priority. The primary strategy for decreasing the rate of late preterm birth must revolve around understanding the indications for these deliveries. Many of the hypertensive disorders of pregnancy, excluding severe preeclampsia, are delivered in the late preterm period without evidence to support this practice. Other soft indications for delivery include oligohydramnios, repeat cesarean, and dichorionic twin gestation. Data are desperately needed to support the practice of early delivery in (continued) 0002-9378/$36.00 • © 2011 Mosby, Inc. All rights reserved. doi: 10.1016/j.ajog.2011.02.004
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Late preterm birth: can be reduced
Late preterm births: irreducible because E ⴝ mc2 Suneet P. Chauhan, MD Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Eastern Virginia Medical Center, Norfolk, VA
D
eliveries at 340/7 to 366/7 weeks, by definition, are late preterm births (LPB). In 2007, of 4,317,119 births in the United States, about 9% (383,792) were LPB; of all births before 37 weeks, almost three-quarters were LPB. Between 1996 and 2006, there has been a 20% increase in the rate of LPB. This increase is alarming because compared with term newborn infants, LPB neonates are at increased risk of morbidity during their perinatal hospitalization (respiratory distress syndrome [RDS], temperature instability), of readmission (hyperbilirubinemia, feeding difficulties) and, most importantly, of neonatal and infant mortality.1 Thus, it is understandable why there is an impetus to decrease the rate of LPB. It might be convenient to accept and encourage a reduction in LPB but it is prudent to acknowledge that current evidence-based knowledge does not allow a safe reduction. There are at least 4 reasons why the rate of LPB is irreducible. First, there are no ACOG practice bulletins or committee opinions on how to decrease the rate. Even the report from the workshop on this topic, did not provide details on how to lower the rate.2 The lack of recommendations means there is insufficient knowledge. Second, E ⫽ mc2 or, stated differently, the Etiology of LPB has Multiple Complex Causes. According to McIntire and Leveno3 approximately 80% of LPB were attributed to idiopathic LPB or ruptured membranes and 20% to obstetric complications like hypertension, abruption, previa, or fetal compromise. The heterogeneity of the causes precludes a simple preventive strategy or randomized clinical trial (RCT). Third, the sample size for a RCT to decrease 1 complication is daunting. As noted by McIntire and Leveno, about 16,000 women need randomization to show a 33% reduction in RDS, if this complication occurs in 1.4%. (continued) JUNE 2011 American Journal of Obstetrics & Gynecology
459
SMFM Debates
these groups of patients because neonatal morbidity and mortality associated with late preterm delivery have been established. f REFERENCES 1. 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. 2. Hamilton BE, Martin JA, Ventura SJ. Births: preliminary data for 2006. Natl Vital Stat Rep 2007;56 3. March of Dimes Perinatal Data Center. Peristats Healthy People 2010. 4. McIntire DD, Leveno KJ. Neonatal mortality and morbidity rates in late preterm births compared with births at term. Obstet Gynecol 2008; 111:35-41. 5. 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.
460
American Journal of Obstetrics & Gynecology JUNE 2011
....................................................................................................................
Dr Gyamfi Bannerman (continued)
www.AJOG.org Dr Chauhan (continued) Fourth, though the rate of preterm birth and LPB has increased, the rate of stillbirth and perinatal mortality for these newborn infants has actually decreased.4,5 In summary, when the cause has multiple complex causes, the rate is difficult to influence. In addition, there is no objective evidence that a decrease is possible, without concomitantly increasing the mortality rate. f REFERENCES 1. Committee on Obstetric Practice. ACOG committee opinion no. 404, April 2008. Late-preterm infants. Obstet Gynecol 2008;111:1029-32. 2. Raju TN, Higgins RD, Stark AR, Leveno KJ. 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. 3. McIntire DD, Leveno KJ. Neonatal mortality and morbidity rates in late preterm births compared with births at term. Obstet Gynecol 2008; 111:35-41. 4. Ananth CV, Gyamfi C, Jain L. Characterizing risk profiles of infants who are delivered at late preterm gestations: does it matter? Am J Obstet Gynecol 2008;199:329-31. 5. Vintzileos AM. Evidence-based compared with reality-based medicine in obstetrics. Obstet Gynecol 2009;113:1335-40.
www. AJOG.org
The editors of the Journal and the SMFM Publication Committee are pleased to provide this summary of a debate conducted at the 31st annual meeting of the Society for Maternal–Fetal Medicine (The Pregnancy Meeting), San Francisco, CA, Feb. 7-12, 2011. One entry in this series will run every month from May through October 2011.
Late preterm birth: can it be reduced? THE ISSUE: Defined as delivery at 340/7-366/7weeks, late preterm births have increased by 15% between 1992 and 2002 and currently they
occur in about 8% of singletons and 35% of multiple gestations. Compared with newborns at 39 weeks, late preterm births undeniably have a significantly higher rate of morbidity (respiratory distress syndrome, pneumonia, need for ventilation), as well as neonatal and infant mortality. Thus, to lower the rate of late preterm birth seems to be self-evident necessity, but there is a need for judicious caution because there is insufficient evidence that prolonging these pregnancies improves maternal-fetal outcomes.
Cynthia Gyamfi Bannerman, MD Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Columbia University Medical Center, New York, NY
L
ate preterm delivery, defined as birth between 34 0/7 to 36 6/7 weeks’ gestation, has increased at a rate higher than that of all preterm birth for the past 20 years.1,2 It has contributed to the shift in the average gestational age at birth from 40 weeks to 39 weeks, and it is driving the increase in prematurity. Each state has seen an increase in late preterm birth, and the increasing incidence has been noted in both singleton and multiple pregnancies.3 The morbidity associated with late preterm birth has been the focus of recent literature, and the importance of these findings must be underscored. Late preterm birth is associated with increased respiratory morbidities, including respiratory distress syndrome, transient tachypnea of the newborn, and the need for ventilatory support.4 It has also been associated with intraventricular hemorrhage, necrotizing enterocolitis, sepsis, hyperbilirubinemia, and feeding difficulties.4,5 Unfortunately, mortality is also increased in this group. Late preterm infants are at a 3- to 6-fold increased risk of death than their term counterparts.1 The morbidity and mortality associated with late preterm birth makes reduction of this phenomenon a priority. The primary strategy for decreasing the rate of late preterm birth must revolve around understanding the indications for these deliveries. Many of the hypertensive disorders of pregnancy, excluding severe preeclampsia, are delivered in the late preterm period without evidence to support this practice. Other soft indications for delivery include oligohydramnios, repeat cesarean, and dichorionic twin gestation. Data are desperately needed to support the practice of early delivery in (continued) 0002-9378/$36.00 • © 2011 Mosby, Inc. All rights reserved. doi: 10.1016/j.ajog.2011.02.004
......................................................................................................................................................................................................
Late preterm birth: can be reduced
Late preterm births: irreducible because E ⴝ mc2 Suneet P. Chauhan, MD Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Eastern Virginia Medical Center, Norfolk, VA
D
eliveries at 340/7 to 366/7 weeks, by definition, are late preterm births (LPB). In 2007, of 4,317,119 births in the United States, about 9% (383,792) were LPB; of all births before 37 weeks, almost three-quarters were LPB. Between 1996 and 2006, there has been a 20% increase in the rate of LPB. This increase is alarming because compared with term newborn infants, LPB neonates are at increased risk of morbidity during their perinatal hospitalization (respiratory distress syndrome [RDS], temperature instability), of readmission (hyperbilirubinemia, feeding difficulties) and, most importantly, of neonatal and infant mortality.1 Thus, it is understandable why there is an impetus to decrease the rate of LPB. It might be convenient to accept and encourage a reduction in LPB but it is prudent to acknowledge that current evidence-based knowledge does not allow a safe reduction. There are at least 4 reasons why the rate of LPB is irreducible. First, there are no ACOG practice bulletins or committee opinions on how to decrease the rate. Even the report from the workshop on this topic, did not provide details on how to lower the rate.2 The lack of recommendations means there is insufficient knowledge. Second, E ⫽ mc2 or, stated differently, the Etiology of LPB has Multiple Complex Causes. According to McIntire and Leveno3 approximately 80% of LPB were attributed to idiopathic LPB or ruptured membranes and 20% to obstetric complications like hypertension, abruption, previa, or fetal compromise. The heterogeneity of the causes precludes a simple preventive strategy or randomized clinical trial (RCT). Third, the sample size for a RCT to decrease 1 complication is daunting. As noted by McIntire and Leveno, about 16,000 women need randomization to show a 33% reduction in RDS, if this complication occurs in 1.4%. (continued) JUNE 2011 American Journal of Obstetrics & Gynecology
459
SMFM Debates
these groups of patients because neonatal morbidity and mortality associated with late preterm delivery have been established. f REFERENCES 1. 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. 2. Hamilton BE, Martin JA, Ventura SJ. Births: preliminary data for 2006. Natl Vital Stat Rep 2007;56 3. March of Dimes Perinatal Data Center. Peristats Healthy People 2010. 4. McIntire DD, Leveno KJ. Neonatal mortality and morbidity rates in late preterm births compared with births at term. Obstet Gynecol 2008; 111:35-41. 5. 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.
460
American Journal of Obstetrics & Gynecology JUNE 2011
....................................................................................................................
Dr Gyamfi Bannerman (continued)
www.AJOG.org Dr Chauhan (continued) Fourth, though the rate of preterm birth and LPB has increased, the rate of stillbirth and perinatal mortality for these newborn infants has actually decreased.4,5 In summary, when the cause has multiple complex causes, the rate is difficult to influence. In addition, there is no objective evidence that a decrease is possible, without concomitantly increasing the mortality rate. f REFERENCES 1. Committee on Obstetric Practice. ACOG committee opinion no. 404, April 2008. Late-preterm infants. Obstet Gynecol 2008;111:1029-32. 2. Raju TN, Higgins RD, Stark AR, Leveno KJ. 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. 3. McIntire DD, Leveno KJ. Neonatal mortality and morbidity rates in late preterm births compared with births at term. Obstet Gynecol 2008; 111:35-41. 4. Ananth CV, Gyamfi C, Jain L. Characterizing risk profiles of infants who are delivered at late preterm gestations: does it matter? Am J Obstet Gynecol 2008;199:329-31. 5. Vintzileos AM. Evidence-based compared with reality-based medicine in obstetrics. Obstet Gynecol 2009;113:1335-40.