title: Mortality risk among preterm babies: immaturity versus underlying pathology.
abstract: BACKGROUND
  Deaths among preterm births are presumably due to both immaturity and the conditions that cause preterm birth. Their relative contributions are unknown.
  
  
  METHODS
  Using US birth certificates (1995-2002), we estimated what portion of preterm neonatal mortality may be attributable to immaturity alone. Twins have elevated mortality, yet they usually have lower mortality than singletons at most preterm weeks. Twinning itself is a cause of early birth. Thus, at any given preterm week, singletons are more likely than twins to have pathologic causes of preterm delivery. If any such cause is associated with a mortality risk higher than that conferred by twinning, it is possible for singletons to have higher mortality than twins at some preterm weeks. Thus, mortality of twins at those weeks comes closer to describing the risk due to immaturity itself. To exclude high-risk babies, we focused on singletons and twins least likely to have suffered fetal growth disruptions (ie, those with "optimal" birth weight). At each gestational week from 24 to 36, we identified (for twins and singletons separately) the 500-gram weight category with the lowest neonatal mortality, and selected the lower of the 2 mortality rates.
  
  
  RESULTS
  Using the above as our best estimates of mortality due to immaturity alone, we calculated that about half the mortality of singleton preterm babies was due to the pathologies that cause early delivery.
  
  
  CONCLUSIONS
  Factors that cause preterm birth apparently contribute a large proportion of preterm mortality. If so, the prevention of preterm mortality requires more than the postponement of delivery.
authors.affiliation: Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA. olga.basso@mcgill.ca
authors.forename: Olga
authors.initials: O
authors.lastname: Basso
authors.forename: Allen
authors.initials: A
authors.lastname: Wilcox
mesh_terms: D005865:Gestational Age; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D007234:Infant, Premature; D007235:Infant, Premature, Diseases / Q000401:mortality*; D012307:Risk Factors; D014310:Triplets; D014427:Twins; D014481:United States / Q000453:epidemiology
references.citation: Obstet Gynecol. 2006 May;107(5):1035-41
references.pmid: 16648408
references.citation: Am J Obstet Gynecol. 1996 May;174(5):1433-40
references.pmid: 9065108
references.citation: Obstet Gynecol. 1995 Feb;85(2):175-82
references.pmid: 7824227
references.citation: Obstet Gynecol. 1996 Feb;87(2):163-8
references.pmid: 8559516
references.citation: Am J Obstet Gynecol. 1998 Jul;179(1):186-93
references.pmid: 9704786
references.citation: Am J Epidemiol. 2000 Dec 15;152(12):1117-9; discussion 1120
references.pmid: 11130616
references.citation: Am J Obstet Gynecol. 1993 May;168(5):1480-5
references.pmid: 8498431
references.citation: Am J Obstet Gynecol. 1979 Apr 15;133(8):899-903
references.pmid: 107803
references.citation: J Perinat Med. 2004;32(1):84-9
references.pmid: 15008394
references.citation: JAMA. 2006 Sep 20;296(11):1357-62
references.pmid: 16985227
references.citation: Am J Epidemiol. 2006 Dec 1;164(11):1115-20
references.pmid: 16931543
references.citation: Epidemiology. 2003 Jul;14(4):490-2
references.pmid: 12843776
references.citation: Am J Obstet Gynecol. 2009 Apr;200(4):372.e1-6
references.pmid: 19217596
references.citation: Am J Epidemiol. 2006 Aug 15;164(4):303-11
references.pmid: 16847040
references.citation: BMC Pregnancy Childbirth. 2004 Apr 16;4(1):7
references.pmid: 15090071
references.citation: Lancet. 2009 Jun 13;373(9680):2000-2
references.pmid: 19523682
references.citation: BMC Pregnancy Childbirth. 2007 Mar 28;7:4
references.pmid: 17391525
references.citation: Am J Epidemiol. 2000 Dec 15;152(12):1107-16
references.pmid: 11130615
references.citation: Am J Epidemiol. 2009 Apr 1;169(7):787-97
references.pmid: 19240224
references.citation: Am J Epidemiol. 2009 Apr 1;169(7):798-801
references.pmid: 19240223
references.citation: BJOG. 2006 Dec;113 Suppl 3:17-42
references.pmid: 17206962
references.citation: Paediatr Perinat Epidemiol. 2007 Sep;21 Suppl 2:22-30
references.pmid: 17803615
references.citation: Pediatrics. 2001 Aug;108(2):E35
references.pmid: 11483845
references.citation: Am J Epidemiol. 1965 Nov;82(3):247-61
references.pmid: 5892596
references.citation: Am J Epidemiol. 2004 Aug 1;160(3):211-2; discussion 215-6
references.pmid: 15257991
references.citation: Paediatr Perinat Epidemiol. 2002 Apr;16(2):181-7
references.pmid: 12064271
references.citation: Obstet Gynecol. 1995 Aug;86(2):200-8
references.pmid: 7617350
references.citation: Obstet Gynecol. 2004 Jul;104(1):78-87
references.pmid: 15229004
references.citation: Pediatrics. 1980 Apr;65(4):735-9
references.pmid: 7367080
references.citation: Int J Epidemiol. 2001 Dec;30(6):1233-41
references.pmid: 11821313
references.citation: Ann Acad Med Singap. 2003 May;32(3):305-10
references.pmid: 12854373
references.citation: Obstet Gynecol. 2007 Apr;109(4):813-22
references.pmid: 17400841
references.citation: Paediatr Perinat Epidemiol. 2007 Sep;21 Suppl 2:86-96
references.pmid: 17803622
references.citation: Lancet. 2008 Jan 5;371(9606):75-84
references.pmid: 18177778
references.citation: Am J Epidemiol. 2008 Apr 1;167(7):786-92
references.pmid: 18343882
references.citation: Am J Obstet Gynecol. 1999 Oct;181(4):773-9
references.pmid: 10521727
references.citation: Int J Epidemiol. 1983 Sep;12(3):319-25
references.pmid: 6685112