Our study shows that fetal malposition at full dilatation is associated with longer second-stage labor and with an increase in a range of indicators of maternal morbidity.
The optimal strategy of management for the second stage of labor would allow the greatest probability of spontaneous delivery with the least risk of maternal and neonatal morbidity. There is, however, a lack of consensus regarding the optimum management of the second stage, including normal duration of second stage. It has been traditionally held that second-stage durations of greater than 2 hours place the baby at increased risk of adverse outcomes.29 More recent data suggest that with careful monitoring of fetal status, a prolonged second stage does not place the baby at increased risk.30–33
An ACOG Practice Bulletin has suggested that in the presence of epidural analgesia, second-stage durations of greater than 2 hours should be considered as prolonged.32 Our data provide partial support for this recommendation. For women experiencing spontaneous vaginal delivery who were advised to commence expulsive efforts at full dilatation (early pushing), the 90th percentile for second-stage duration was 3.0 hours, 2.8 hours, and 2.8 hours for occiput posterior, occiput transverse, and occiput anterior positions, respectively (data not shown). For women with spontaneous vaginal deliveries who were exposed to a policy of delayed pushing, the 90th percentile for the second-stage duration was 4.9 hours, 4.9 hours, and 3.9 hours for occiput posterior, occiput transverse, and occiput anterior positions, respectively (data not shown). For women experiencing operative delivery, the 90th percentile ranged from 4.6 hours (early pushing, occiput anterior position) to 6.3 hours (delayed pushing, occiput transverse position) (data not shown). Our results demonstrate that in nulliparous women under continuous epidural analgesia, the assessment of fetal position at full dilatation is an important determinant of second-stage duration. Guidelines that propose norms for expected labor duration should take into consideration position of the fetal head at full dilatation and the strategy of pushing. Our data suggest that the current recommendations of 2 hours for patients with epidural may be too restrictive, particularly when a policy of delayed pushing is practiced. With respect to maternal morbidity indicators, women in the “missing” category had rates that were intermediately between women in the occiput anterior group and those in the occiput transverse group, suggesting that the “missing” group was composed of a mix of fetal head positions.
Cephalohematoma was significantly more frequent in the “missing” group (16.9% missing compared with 4.5% occiput transverse compared with 5.0% occiput anterior compared with 6.7% occiput posterior; P < .001), whereas other forms of trauma were distributed similarly across groups. This could suggest that the fetuses in the missing category had significant molding at full dilatation that made the determination of the position more difficult and that also predisposed to the diagnosis of cephalohematoma.
In this low-risk obstetric population, the proportion of women with occiput posterior position at full dilatation was 13.1%, whereas the proportion was 12.4% for the occiput transverse position. A prospective study published as an abstract reported a 41.0% prevalence of occiput posterior positions and 44.5% of occiput transverse positions at hospital admission (Bernstein PC, Choi Y. Am J Obstet Gynecol 1999). In a prospective study using intrapartum sonography, Gardberg et al3 observed a prevalence of occiput posterior positions of 15% when women arrived in the delivery ward. Phillips and Freeman2 reported an incidence of occiput posterior positions of 10–20% early in labor, not specifying the precise moment that the head position was diagnosed. No separate data for occiput transverse positions early in labor were found in the literature.
Our results show no statistically significant differences in the duration of the first stage of labor according to fetal position at full cervical dilatation. Similarly, Gardberg et al3 and Calkins8 found no evidence of difference in the duration of the first stage between occiput anterior and occiput posterior positions diagnosed at delivery. Phillips and Freeman2 observed an increase of 84 minutes in the mean duration of the first stage of labor when the occiput posterior position persisted until delivery. No statistical analyses were mentioned.
The patient selection in this study could have resulted in a selection bias with respect to the absence of association between fetal position and the first stage of labor duration. Because our study assessed an approach to care in the second stage, patients having a first-stage cesarean delivery for slow labor progress were excluded.
We found a 46-minute increase in mean second-stage duration for patients with fetal malpositions at full dilatation compared with those in the occiput anterior positions. Phillips et al2 noted a 25-minute mean increase in the duration of the second stage of labor when the occiput posterior position of the fetal head persisted until delivery. Pearl et al's7 retrospective study found a statistically significant prolongation of the second stage of labor in persistent occiput posterior position deliveries (45.3 ± 46.5 minutes for occiput anterior compared with 60.1 ± 50.8 minutes for occiput posterior in spontaneous delivery, P < .05; and 117.9 ± 78.6 minutes for occiput anterior compared with 128.0 ± 76.6 minutes for occiput posterior in operative delivery, P < .05). Occiput transverse positions were not assessed in this study. Our findings of no significant differences in risk of abnormal Apgar scores or neonatal intensive care unit admission according to fetal position are similar to those of previous studies.2,3
Our observation of higher rates of severe perineal tears in women whose baby was in an occiput posterior and occiput transverse position is at least partly explained by higher incidences of midpelvic and rotational instrumental procedures. This observation is consistent with the results of previous studies.2 Calkin8 observed a frequency of 20% of injuries to soft tissues when the fetus had a posterior position during labor. The incidence of third-degree tear was 1.6% for posterior positions, compared with 10.0% in our study. Paradoxically, in Calkin's study, a higher rate of low forceps was reported: 65% compared with 8.1% in our study for posterior positions. In Calkin's publication, there was no comparison group.
It should be noted that most of the literature assessing the effects of fetal malposition has described the position of the presenting part at delivery,8,9,11,26 or has focused only on persistent occiput posterior positions (Bernstein PC, Choi Y. Am J Obstet Gynecol 1999).2,7,23,27 In our study, the position of the fetal head was documented at full dilatation. The position of the head at delivery was documented only in cases with forceps or vacuum. However, fetal position at the time of delivery was not documented for spontaneous vaginal deliveries. It was thus impossible to determine the proportion of women spontaneously delivering a baby in occiput posterior or occiput transverse position.
We observed a higher risk of estimated blood loss of more than 500 mL in the transverse and posterior positions group. This can be partially attributed to a higher rate of cesarean delivery in these groups. We verified whether fetal position was associated with a higher risk of blood transfusions. In our study, only 8 patients had blood transfusion (0.5% in occiput posterior, 1.0% in occiput transverse, 0.3% in occiput anterior, and 0.4% in the missing positions group).
In the trial on which this study was based, the indications for oxytocin treatment during the second stage of labor were standardized to minimize the potential for confounding by this variable. The epidural analgesia technique was also standardized.24 This should have avoided any confounding that could have resulted from imbalances in the epidural analgesia technique. Previous studies indicate that epidural increases the risk of fetal malposition at delivery.23 The motor block associated with epidural administration could cause pelvic muscle relaxation, which could prevent fetal rotation to an anterior rotation.28 In an observational study, the median duration of the second stage for nulliparous women experiencing spontaneous vaginal delivery was approximately 120 minutes in the presence of epidural as opposed to 60 minutes in its absence.20 Clinical trials comparing epidural to nonepidural forms of pain relief have also found epidural analgesia to prolong the second stage, and to increase the need for assisted vaginal delivery.16
In conclusion, the risk of maternal morbidity was significantly increased with occiput posterior and occiput transverse positions at full dilatation: cesarean delivery risk was increased by nearly 2-fold for occiput transverse and more than 4-fold for occiput posterior positions. Midpelvic procedures were increased almost by 3-fold with occiput posterior positions. Episiotomy and third- and fourth-degree tears were also increased in patients with occiput posterior and occiput transverse positions at full dilatation. Thus, fetal malposition is a risk factor for prolonged second stage as well as for maternal morbidity.
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7. Pearl ML, Roberts JM, Laros RK, Hurd WW. Vaginal delivery from the persistent occiput posterior position Influence on maternal and neonatal morbidity. J Reprod Med 1993;38:955–61.
8. Calkins L. Occiput posterior presentation. Obstet Gynecol 1953;1:466–71.
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23. Fitzpatrick M, McQuillan K, O'Herlihy C. Influence of persistent occiput posterior position on delivery outcome. Obstet Gynecol 2001;98:1027–31.
24. Fraser WD, Marcoux S, Krauss I, Douglas J, Goulet C, Boulvain M. Multicenter, randomized, controlled trial of delayed pushing for nulliparae women in the second stage of labor with continuous epidural analgesia The PEOPLE (Pushing Early or Pushing Late with Epidural) Study Group. Am J Obstet Gynecol 2000;182:1165–72.
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Other members of the Pushing Early Or Pushing Late with Epidural (PEOPLE) Study Group include:
William D. Fraser, MD, MSc
Sylvie Marcoux, MD, PhD
Isabelle Krauss, MD, MSc
Joanne Douglas, MD
Céline Goulet, RN, PhD
Investigators and research assistants:
J. Chabot, MD; J. Flammand, RN; L. Laperrière, BN. CHUQ-Pavillon St-François d'Assise, Québec, Québec, Canada.
P. Fish, MD; G. Hamel, RN. Hôpital de Chicoutimi, Chicoutimi, Québec, Québec, Canada.
R. Sabbah, MD; L. Vincelli. Hôpital Sacré-Cœur de Montréal, Montréal, Québec. Canada.
G. Tawagi, MD; O. Rosag, MD; J. Belcher, RN. Ottawa Civic Hospital, Ottawa, Ontario, Canada.
F. Galerneau, MD; M. Klein, MD; J. Swenerton, MD; B. Weibe, RN; E. Nickel, RN. BC Women's Hospital, Vancouver, British Columbia, Canada.
K. Milne, MD; J. Fuller, MD; L. Watson, RN. St-Joseph's Hospital, London, Ontario. Canada.
O. Irion, MD; K. Rifat, MD; V. Mentha (midwife). Hôpitaux Universitaires de Genève, Geneva, Switzerland.
S. Bottoms, MD; B. Steffy, RN. Hutzel Hospital, Detroit, Michigan, United States.
M. Helewa, MD; S. Lucy, MD; S. Erickson, RN. St-Boniface Hospital, Winnipeg, Manitoba, Canada.
N. Okun, MD; A. Guest, MD; A. Stuart, MD; D. Schimeck, RN. University of Alberta Hospital, Edmonton, Alberta, Canada.
M. Sermer, MD; M. Bailey, RN. Toronto General Hospital, Toronto, Ontario, Canada.
D. Blouin, MD; Y. Claprood, MD; D. Beaulieu, RN. Centre hospitalier universitaire de l'Estrie, Sherbrooke, Québec, Canada.
Data Management Committee:
Michel Boulvain, MD, PhD
Sylvie Bérubé, PhD
Safety and Efficacy Monitoring Committee:
François Meyer, MD, PhD
Aida Bairam, MD, PhD
Jean-Marie Moutquin, MD