title: Cephalopelvic disproportion is associated with an altered uterine contraction shape in the active phase of labor.
abstract: OBJECTIVE
  The purpose of this study was to determine if intrapartum contractions of a particular shape (rapid rise with slower return to baseline) are predictive of cephalopelvic disproportion (CPD).
  
  
  METHODS
  In an institutional review board (IRB)-approved study, cohorts of 100 women who underwent spontaneous vaginal delivery (SVD) and 100 who underwent cesarean section (C/S) for CPD or arrest of labor were consecutively identified between January 2004 and March 2005. Inclusion criteria included term, singleton pregnancies, nulliparity, and absence of fetal anomalies. One hour of interpretable electronic fetal monitoring (EFM) was obtained in active labor. Fall to rise (F:R) ratio was calculated by measuring the time for a contraction to return to its baseline from its peak ("fall") and the time for a contraction to rise to its peak ("rise"). The F:Rs were then averaged over the number of contractions. Data were analyzed using Student t test, Chi-square, and Fisher exact tests where appropriate.
  
  
  RESULTS
  Maternal demographics are listed in Table I. The average F:R ratio was 1.55 for SVD versus 1.77 for C/S, a statistically significant difference (P = .00003). Analysis of variance revealed this difference persists when controlled for the potentially confounding factors shown. At F:R >1.76, moreover, there was a trend towards larger birth weight (P = .06).
  
  
  CONCLUSIONS
  Our study demonstrates there is a difference in uterine contraction configuration that is more common in those labors destined for C/S due to CPD. This may indicate the presence of a heretofore unknown feedback mechanism as the uterus adapts to the dysfunctional labor.
authors.affiliation: Division of Maternal Fetal Medicine, Department of Gynecology and Obstetrics, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Janyne E
authors.initials: JE
authors.lastname: Althaus
authors.forename: Scott
authors.initials: S
authors.lastname: Petersen
authors.forename: Rita
authors.initials: R
authors.lastname: Driggers
authors.forename: Alice
authors.initials: A
authors.lastname: Cootauco
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Bienstock
authors.forename: Karin J
authors.initials: KJ
authors.lastname: Blakemore
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D052178:Cephalopelvic Disproportion / Q000175:diagnosis* / Q000503:physiopathology; D005260:Female; D006801:Humans; D007745:Labor Onset; D011247:Pregnancy; D014590:Uterine Contraction / Q000502:physiology*; D018590:Uterine Monitoring; D014599:Uterus / Q000502:physiology*