title: Evidence to support that spontaneous preterm labor is adaptive in nature: neonatal RDS is more common in "indicated" than in "spontaneous" preterm birth.
abstract: OBJECTIVE
  The onset of preterm labor has been proposed to have survival value and to be adaptive in nature. This hypothesis would predict that induced preterm birth may be associated with higher rates of complications than spontaneous preterm birth. The purpose of this study was to determine if there is a difference in the frequency of neonatal respiratory distress syndrome (RDS), the most common neonatal complication, according to the etiology of preterm birth (e.g., preterm labor [PTL], preterm PROM, or pregnancies which ended because of maternal-fetal indications).
  
  
  METHODS
  The relationship between the occurrence of RDS and the obstetrical circumstances leading to preterm birth was examined in 257 consecutive singleton preterm births (gestational age: 24-32 weeks). Cases with major congenital anomalies were excluded. The study population was divided into two groups according to the cause of preterm birth: 1) preterm birth due to PTL with intact membranes or preterm PROM (spontaneous preterm birth group); and 2) preterm birth due to maternal or fetal indications (indicated preterm birth group).
  
  
  RESULTS
  1) RDS was diagnosed in 47% of cases; 2) RDS was more common in patients with indicated preterm birth than in those with spontaneous preterm birth group (58.1% vs. 38.4%, P=0.002); 3) Patients with indicated preterm birth had a significantly higher mean gestational age at birth, but lower mean birth weight, lower rate of histological chorioamnionitis and higher rates of cesarean delivery, 5 min Apgar score of <7, and umbilical arterial blood pH of <7.15 than those with spontaneous preterm birth (P<0.05 for each); 4) Antenatal corticosteroids were used in 73.4% of cases with indicated preterm birth and in 76.9% of those with spontaneous preterm birth; 5) Multivariate analysis demonstrated that indicated preterm birth was associated with an increased risk of RDS after adjusting for confounding variables (OR=2.29, 95% CI 1.22-4.29).
  
  
  CONCLUSIONS
  1) The rate of RDS is greater following "indicated" rather than spontaneous preterm birth; 2) This observation supports the view that spontaneous preterm labor is adaptive in nature.
authors.affiliation: Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Joonho
authors.initials: J
authors.lastname: Lee
authors.forename: Hyo Suk
authors.initials: HS
authors.lastname: Seong
authors.forename: Byoung Jae
authors.initials: BJ
authors.lastname: Kim
authors.forename: Jong Kwan
authors.initials: JK
authors.lastname: Jun
authors.forename: Roberto
authors.initials: R
authors.lastname: Romero
authors.forename: Bo Hyun
authors.initials: BH
authors.lastname: Yoon
mesh_terms: D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007751:Labor, Induced / Q000009:adverse effects*; D008297:Male; D007752:Obstetric Labor, Premature / Q000503:physiopathology*; D016017:Odds Ratio; D011247:Pregnancy; D012127:Respiratory Distress Syndrome, Newborn; D012189:Retrospective Studies