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Reply: Why does fetal head rotation occur in spontaneous labor?

  • Hulda Hjartardóttir
    Affiliations
    Department of Obstetrics and Gynecology, Landspitali—The National University Hospital of Iceland, Reykjavik, Iceland
    Faculty of Medicine, University of Iceland, Reykjavik, Iceland
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  • Torbjørn M. Eggebø
    Affiliations
    National Center for Fetal Medicine, St. Olavs Hospital, Trondheim University Hospital, Trondheim, Norway
    Department of Clinical and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway
    Department of Obstetrics and Gynecology, Stavanger University Hospital, Stavanger, Norway
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      We appreciate the interest shown by Drs Ross and Gemert in our recent publication on the ultrasound study of fetal head rotation during spontaneous labor in nulliparous women.
      • Hjartardóttir H.
      • Lund S.H.
      • Benediktsdóttir S.
      • Geirsson R.T.
      • Eggebø T.M.
      When does fetal head rotation occur in spontaneous labor at term: results of an ultrasound-based longitudinal study in nulliparous women.
      The combined use of transabdominal and transperineal ultrasound methods opens up a new and more detailed way of studying the rotation of the fetal head, including the possible effects of epidural analgesia on this mechanism. The points specifically raised in the letter considered the effect epidural analgesia may have on the pelvic floor, relaxing the muscles and thereby, reducing the resistance provided by the pelvic floor. This resistance is thought to be necessary for successful rotation of the fetal head to the most favorable occiput anterior position. To answer the questions raised and shed some light on the association between epidural analgesia use and persistent occiput posterior (OP) position, that is, the number of neonates delivered in the OP position, we have examined our data further. Of the 99 women included in the study, 61 had an epidural analgesia administered during labor. The details of the epidural analgesia used can be found in another recent publication in which we presented the labor descent patterns for the same study group.
      • Hjartardóttir H.
      • Lund S.H.
      • Benediktsdóttir S.
      • Geirsson R.T.
      • Eggebø T.M.
      Fetal descent in nulliparous women assessed by ultrasound: a longitudinal study.
      The research question that involved whether epidural analgesia increased the risk of persistent OP position was a complex one. Moreover, one of the main issues was whether more women need epidural analgesia when laboring with a fetus in an OP position compared with those with fetuses in other positions and whether this might be related to the increased numbers of persistent OP positions at birth. In our population, the frequency of OP position at delivery in women having epidural analgesia administered during labor was 20% (12 of 61 cases) vs 5% (2 of 38 cases), which in our calculations did not reach significance (P=.07). The frequency of women having epidural analgesia administered during labor was 61% (37 of 61 cases) when the fetus was in an OP position at admission vs 40% (15 of 38 cases) (P=.06). Data were analyzed with the statistical software package R Core Team (R Foundation for Statistical Computing, Vienna, Austria) as described in the original article. In our publication on the descent patterns, almost identical patterns were demonstrated in women with and without epidural analgesia. Moreover, our results agreed with that of the old clinical studies by Calkins et al
      • Calkins L.A.
      Occiput posterior: incidence, significance, and management.
      and the study of Lieberman et al
      • Lieberman E.
      • Davidson K.
      • Lee-Parritz A.
      • Shearer E.
      Changes in fetal position during labor and their association with epidural analgesia.
      that rotation is a very late event in labor and that most OP positions, even late in labor, rotate to the anterior position. Although we cannot confirm the findings of Lieberman et al
      • Lieberman E.
      • Davidson K.
      • Lee-Parritz A.
      • Shearer E.
      Changes in fetal position during labor and their association with epidural analgesia.
      that there is an association between epidural analgesia and persistent OP position at birth, the theory is plausible, and we acknowledge that our study did not have the power to make a firm conclusion in this regard. Ultrasound methods offer an excellent tool for studying labor mechanics in more detail than was previously possible, and we would welcome further studies of both larger and dissimilar groups of women. Our results may assist in designing such studies in which the effects of epidural analgesia on rotation and position at birth would be the main object.

      References

        • Hjartardóttir H.
        • Lund S.H.
        • Benediktsdóttir S.
        • Geirsson R.T.
        • Eggebø T.M.
        When does fetal head rotation occur in spontaneous labor at term: results of an ultrasound-based longitudinal study in nulliparous women.
        Am J Obstet Gynecol. 2021; 224: 514.e1-514.e9
        • Hjartardóttir H.
        • Lund S.H.
        • Benediktsdóttir S.
        • Geirsson R.T.
        • Eggebø T.M.
        Fetal descent in nulliparous women assessed by ultrasound: a longitudinal study.
        Am J Obstet Gynecol. 2021; 224: 378.e1-378.e15
        • Calkins L.A.
        Occiput posterior: incidence, significance, and management.
        Am J Obstet Gynecol. 1939; 38: 993-1001
        • Lieberman E.
        • Davidson K.
        • Lee-Parritz A.
        • Shearer E.
        Changes in fetal position during labor and their association with epidural analgesia.
        Obstet Gynecol. 2005; 105: 974-982

      Linked Article

      • Why does fetal head rotation occur in spontaneous labor?
        American Journal of Obstetrics & GynecologyVol. 225Issue 5
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          We read with interest the article by Hjartardóttir et al,1 in which the authors demonstrated that the most common fetal head position was occiput posterior (OP) throughout the first stage of labor, and occiput anterior (OA) after the head descended below the midpelvis. Although the report provided important insights in OP to OA rotation with and without oxytocin augmentation, the authors did not report the incidence of or its relation to epidural use. The benefits of the smaller fetal head diameters in the OA flexed position are well recognized.
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