title: [Change of labor duration:a systematic analysis].
abstract: OBJECTIVE
  To evaluate the labor duration of healthy primiparas in the past 20 years compared with Friedman labor curve.
  
  
  METHODS
  Published observational studies about labor duration in primiparas with singleton vertex presentation were searched in PubMed, EMBase, Cochrane library, CNKI, VIP and Wanfang database. The Cochrane Collaboration's RevMan 5.1 software was used for meta-analysis.
  
  
  RESULTS
  Eleven literatures involving 4534 primiparas were included, which were eligible for the criteria to investigate the labor duration. Meta-analysis showed that the length of active phase was significantly different between what was showed in primiparas in the past 20 years and Friedman labor curve [P = 0.01, weighted mean difference (WMD) = 1.61, 95%CI: 0.38 to 2.83], and significant differences were also found in the second stage duration (P = 0.0006, WMD = -0.20, 95%CI: -0.31 to -0.09).
  
  
  CONCLUSIONS
  Compared with Friedman labor curve, active phase length of healthy primiparas in the past 20 years was significantly longer and second stage length was shorter. Reassessing labor curve of healthy primiparas is required for more scientific guidance and less unnecessary interventions.
authors.affiliation: Department of Clinical Medicine, Medical School of Nanjing University, China.
authors.forename: Ling
authors.initials: L
authors.lastname: Yang
authors.forename: Bi-yun
authors.initials: BY
authors.lastname: Xu
authors.forename: Ya-li
authors.initials: YL
authors.lastname: Hu
mesh_terms: D000328:Adult; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D007745:Labor Onset; D007747:Labor Stage, First / Q000502:physiology*; D007748:Labor Stage, Second / Q000502:physiology*; D007743:Labor, Obstetric / Q000502:physiology; D009321:Natural Childbirth / Q000451:nursing; D010298:Parity; D011247:Pregnancy; D012016:Reference Values; D013997:Time Factors; D055815:Young Adult