title: Heterogeneity of preterm birth subtypes in relation to neonatal death.
abstract: OBJECTIVE
  To investigate the heterogeneity of preterm labor, preterm premature rupture of membranes (PROM), and indicated preterm birth in overall and gestational-age-specific neonatal death risk.
  
  
  METHODS
  We used 2001 U.S. linked birth/infant death (birth cohort) data sets for this analysis. We categorized three preterm birth subtypes according to reported preterm PROM, induction of labor, cesarean delivery, and pregnancy and labor complications. We used Cox proportional hazard models to calculate covariates adjusted hazard ratios (HRs) for neonatal death (0-27 days of life) among preterm neonates born at 24-27, 28-31, 32-33, and 34-36 weeks of gestation, with preterm labor being the referent.
  
  
  RESULTS
  There were 3,763,306 singleton live births at 24-44 weeks of gestation in the data set. Preterm PROM, indicated preterm birth, and preterm labor had neonatal death risk of 2.7%, 1.8%, and 1.1%, respectively. Compared with preterm labor, preterm PROM had shorter gestational age and lower birth weight, so did indicated preterm birth but to a lesser extent. Preterm PROM and indicated preterm birth after 28 weeks of gestation were associated with higher neonatal death risk than preterm labor. At 34-36 weeks of gestation, the HR of preterm PROM was 1.53 (95% confidence interval 1.20-1.95), and the HR of indicated preterm birth was 2.06 (95% confidence interval 1.83-2.33). The increased risk from preterm PROM and indicated preterm birth was not limited to early neonatal death in the first 7 days.
  
  
  CONCLUSIONS
  Preterm PROM and indicated preterm birth had higher risk of neonatal death than preterm labor, indicating heterogeneity in gestational age distribution and gestational-age-specific neonatal death risk.
  
  
  METHODS
  II.
authors.affiliation: From the Department of Preventive Medicine and Public Health, Creighton University School of Medicine; Department of Epidemiology, College of Public Health, University of Nebraska Medical Center; and Department of Obstetrics and Gynecology, Creighton University School of Medicine, Omaha, Nebraska.
authors.forename: Aimin
authors.initials: A
authors.lastname: Chen
authors.forename: Shingairai A
authors.initials: SA
authors.lastname: Feresu
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Barsoom
mesh_terms: D000328:Adult; D002585:Cesarean Section; D015331:Cohort Studies; D005260:Female; D005322:Premature Rupture of Fetal Membranes / Q000453:epidemiology*; D005865:Gestational Age; D006801:Humans; D007226:Infant Mortality; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007234:Infant, Premature; D008297:Male; D007752:Obstetric Labor, Premature / Q000453:epidemiology*; D011247:Pregnancy; D016016:Proportional Hazards Models; D012307:Risk Factors; D014481:United States / Q000453:epidemiology; D055815:Young Adult
references.citation: Cunningham FG, Leveno KJ, Bloom SL, Hauth JC, Gilstrap LC III, Wenstrom KD. Williams obstetrics. 22nd ed. New York (NY): McGraw-Hill Medical Publishing Division; 2005.
references.citation: Ananth CV, Vintzileos AM. Epidemiology of preterm birth and its clinical subtypes. J Matern Fetal Neonatal Med 2006;19:773–82.
references.citation: Savitz DA, Blackmore CA, Thorp JM. Epidemiologic characteristics of preterm delivery: etiologic heterogeneity. Am J Obstet Gynecol 1991;164:467–71.
references.citation: Berkowitz GS, Blackmore-Prince C, Lapinski RH, Savitz DA. Risk factors for preterm birth subtypes. Epidemiology 1998;9:279–85.
references.citation: Zhang J, Savitz DA. Preterm birth subtypes among blacks and whites. Epidemiology 1992;3:428–33.
references.citation: Villar J, Abalos E, Carroli G, Giordano D, Wojdyla D, Piaggio G, et al. Heterogeneity of perinatal outcomes in the preterm delivery syndrome. Obstet Gynecol 2004;104:78–87.
references.citation: Callaghan WM, MacDorman MF, Rasmussen SA, Qin C, Lackritz EM. The contribution of preterm birth to infant mortality rates in the United States. Pediatrics 2006;118:1566–73.
references.citation: Morken NH, Kallen K, Jacobsson B. Outcomes of preterm children according to type of delivery onset: a nationwide population-based study. Paediatr Perinat Epidemiol 2007;21:458–64.
references.citation: Martin JA, Hamilton BE, Ventura SJ, Menacker F, Park MM, Sutton PD. Births: final data for 2001. Natl Vital Stat Rep 2002;51:1–102.
references.citation: 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.
references.citation: Nohr EA, Bech BH, Vaeth M, Rasmussen KM, Henriksen TB, Olsen J. Obesity, gestational weight gain and preterm birth: a study within the Danish National Birth Cohort. Paediatr Perinat Epidemiol 2007;21:5–14.
references.citation: Nohr EA, Vaeth M, Bech BH, Henriksen TB, Cnattingius S, Olsen J. Maternal obesity and neonatal mortality according to subtypes of preterm birth. Obstet Gynecol 2007;110:1083–90.
references.citation: Ananth CV, Getahun D, Peltier MR, Salihu HM, Vintzileos AM. Recurrence of spontaneous versus medically indicated preterm birth. Am J Obstet Gynecol 2006;195:643–50.
references.citation: Barros FC, Vélez Mdel P. Temporal trends of preterm birth subtypes and neonatal outcomes. Obstet Gynecol 2006;107:1035–41.
references.citation: Kurkinen-Raty M, Koivisto M, Jouppila P. Preterm delivery for maternal or fetal indications: maternal morbidity, neonatal outcome and late sequelae in infants. BJOG 2000;107:648–55.
references.citation: Goldenberg RL, Hauth JC, Andrews WW. Intrauterine infection and preterm delivery. N Engl J Med 2000;342:1500–7.
references.citation: Goldenberg RL, Culhane JF, Iams JD, Romero R. Epidemiology and causes of preterm birth. Lancet 2008;371:75–84.
references.citation: Arias F, Rodriquez L, Rayne SC, Kraus FT. Maternal placental vasculopathy and infection: two distinct subgroups among patients with preterm labor and preterm ruptured membranes. Am J Obstet Gynecol 1993;168:585–91.
references.citation: Behrman RE, Stith Butler A, editors. Institute of Medicine, Committee on Understanding Preterm Birth and Assuring Healthy Outcomes, Board on Health Sciences Policy. Preterm Birth: Causes, Consequences, and Prevention. Washington, DC: The National Academies Press; 2007.
references.citation: Ananth CV, Vintzileos AM. Medically indicated preterm birth: recognizing the importance of the problem. Clin Perinatol 2008;35:53–67.
references.citation: Ananth CV, Vintzileos AM. Maternal–fetal conditions necessitating a medical intervention resulting in preterm birth. Am J Obstet Gynecol 2006;195:1557–63.
references.citation: Himes KP, Simhan HN. Risk of recurrent preterm birth and placental pathology. Obstet Gynecol 2008;112:121–6.
references.citation: Pasquier JC, Bujold E, Rabilloud M, Picaud JC, Ecochard R, Claris O, et al. Effect of latency period after premature rupture of membranes on 2 years infant mortality (DOMINOS study). Eur J Obstet Gynecol Reprod Biol 2007;135:21–7.
references.citation: Ernest JM. Neonatal consequences of preterm PROM. Clin Obstet Gynecol 1998;41:827–31.
references.citation: Lee T, Silver H. Etiology and epidemiology of preterm premature rupture of the membranes. Clin Perinatol 2001;28:721–34.
references.citation: Mercer BM. Preterm premature rupture of the membranes. Obstet Gynecol 2003;101:178–93.
references.citation: Chauhan SP, Magann EF, Scott JR, Scardo JA, Hendrix NW, Martin JN Jr. Cesarean delivery for fetal distress: rate and risk factors. Obstet Gynecol Surv 2003;58:337–50.
references.citation: American College of Obstetricians and Gynecologists. ACOG Committee Opinion No. 394, December 2007. Cesarean delivery on maternal request. Obstet Gynecol 2007;110:1501.
references.citation: Ananth CV. Menstrual versus clinical estimate of gestational age dating in the United States: temporal trends and variability in indices of perinatal outcomes. Paediatr Perinat Epidemiol 2007;21 suppl:22–30.