Birth simulator: reliability of transvaginal assessment of fetal head station as defined by the American College of Obstetricians and Gynecologists classification

Am J Obstet Gynecol. 2005 Mar;192(3):868-74. doi: 10.1016/j.ajog.2004.09.028.


Objective: This study was undertaken to investigate the reliability of transvaginal assessment of fetal head station by using a newly designed birth simulator.

Study design: This prospective study involved 32 residents and 25 attending physicians. Each operator was given all 11 possible fetal stations in random order. A fetal head mannequin was placed in 1 of the 11 American College of Obstetricians and Gynecologists (ACOG) stations (-5 to +5) in a birth simulator equipped with real-time miniaturized sensor. The operator then determined head position clinically using the ACOG classification. Head position was described as: (1) "engaged" or "nonengaged" (engagement code); (2) "high," "mid," "low," or "outlet" (group code); and (3) according to the 11 ACOG ischial spine stations (numerical code). Errors were defined as differences between the stations given by the sensor and by the operator. We determined the error rates for the 3 codes.

Results: "Numerical" errors occurred in 50% to 88% of cases for residents and in 36% to 80% of cases for attending physicians, depending on the position. The mean "group" error was 30% (95% CI 25%-35%) for residents and 34% (95% CI 27%-41%) for attending physicians. In most cases (87.5% for residents and 66.8% for attending physicians) of misdiagnosis of "high" station, the "mid" station was retained. Residents and attending physicians made an average of 12% of "engagement" errors, equally distributed between false diagnosis of engagement and nonengagement.

Conclusion: Our results show that transvaginal assessment of fetal head station is poorly reliable, meaning clinical training should be promoted. The choice not to perform vaginal delivery when the fetus is in the "mid" position strongly decreases the risk of applying instruments on an undiagnosed "high" station. Conversely, obstetricians who perform only "low" operative vaginal deliveries also deliver unrecognized "mid" station fetuses. Therefore, residency programs should offer training in "mid" pelvic operative vaginal deliveries. Birth simulators could be used in training programs.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial

MeSH terms

  • Delivery, Obstetric* / methods
  • Female
  • Head
  • Humans
  • Labor Presentation*
  • Pregnancy
  • Prospective Studies