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The sonographic measurement of the ratio between the fetal head circumference and the obstetrical conjugate is accurate in predicting the risk of labor arrest: results from a multicenter prospective study

  • Elvira Di Pasquo
    Affiliations
    Department of Obstetrics and Gynecology, University Hospital of Parma, Parma, Italy (Drs Di Pasquo, Morganelli, Volpe, Labadini, Ramirez Zegarra, Dall'Asta, and Ghi)
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  • Giovanni Morganelli
    Affiliations
    Department of Obstetrics and Gynecology, University Hospital of Parma, Parma, Italy (Drs Di Pasquo, Morganelli, Volpe, Labadini, Ramirez Zegarra, Dall'Asta, and Ghi)
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  • Nicola Volpe
    Affiliations
    Department of Obstetrics and Gynecology, University Hospital of Parma, Parma, Italy (Drs Di Pasquo, Morganelli, Volpe, Labadini, Ramirez Zegarra, Dall'Asta, and Ghi)
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  • Corinne Labadini
    Affiliations
    Department of Obstetrics and Gynecology, University Hospital of Parma, Parma, Italy (Drs Di Pasquo, Morganelli, Volpe, Labadini, Ramirez Zegarra, Dall'Asta, and Ghi)
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  • Ruben Ramirez Zegarra
    Affiliations
    Department of Obstetrics and Gynecology, University Hospital of Parma, Parma, Italy (Drs Di Pasquo, Morganelli, Volpe, Labadini, Ramirez Zegarra, Dall'Asta, and Ghi)

    Department of Obstetrics and Gynecology, St. Joseph Krankenhaus, Berlin, Germany (Drs Ramirez Zegarra and Abou-Dakn)
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  • Michael Abou-Dakn
    Affiliations
    Department of Obstetrics and Gynecology, St. Joseph Krankenhaus, Berlin, Germany (Drs Ramirez Zegarra and Abou-Dakn)
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  • Ilenia Mappa
    Affiliations
    Department of Obstetrics and Gynecology Medicine, Fondazione Policlinico Tor Vergata, University of Rome Tor Vergata, Rome, Italy (Drs Mappa and Rizzo)
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  • Giuseppe Rizzo
    Affiliations
    Department of Obstetrics and Gynecology Medicine, Fondazione Policlinico Tor Vergata, University of Rome Tor Vergata, Rome, Italy (Drs Mappa and Rizzo)
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  • Andrea Dall'Asta
    Affiliations
    Department of Obstetrics and Gynecology, University Hospital of Parma, Parma, Italy (Drs Di Pasquo, Morganelli, Volpe, Labadini, Ramirez Zegarra, Dall'Asta, and Ghi)

    Department of Medicine and Surgery, Obstetrics and Gynaecology Unit, University of Parma, Parma, Italy (Drs Dall'Asta and Ghi)
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  • Tullio Ghi
    Correspondence
    Corresponding author: Tullio Ghi, PhD.
    Affiliations
    Department of Obstetrics and Gynecology, University Hospital of Parma, Parma, Italy (Drs Di Pasquo, Morganelli, Volpe, Labadini, Ramirez Zegarra, Dall'Asta, and Ghi)

    Department of Medicine and Surgery, Obstetrics and Gynaecology Unit, University of Parma, Parma, Italy (Drs Dall'Asta and Ghi)
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      BACKGROUND

      Labor arrest is estimated to account for approximately one-third of all primary cesarean deliveries, and is associated with an increased risk of adverse maternal and perinatal outcomes. One of the main causes is the mismatch between the size of the birth canal and that of the fetus, a condition usually referred to as cephalopelvic disproportion.

      OBJECTIVE

      This study aimed to describe a new ultrasound predictor of labor arrest leading to cesarean delivery because of suspected cephalopelvic disproportion.

      STUDY DESIGN

      This was a multicenter prospective study conducted at 3 maternity units from January 2021 to January 2022. A nonconsecutive series of singleton pregnancies with cephalic-presenting fetuses, gestational age of 34 weeks+0 days or above, and no contraindication to vaginal delivery attending at the antenatal clinics of each institution were considered eligible. Between 34+0 and 38+0 weeks of gestation, all eligible patients were submitted to transabdominal 2D ultrasound measurement of the obstetrical conjugate. On admission to the labor ward, the fetal head circumference was measured on the standard transthalamic plane by transabdominal ultrasound. The primary outcome of the study was the accuracy of the ratio between the fetal head circumference and the obstetrical conjugate measurement (ie, head circumference/obstetrical conjugate ratio) in predicting the occurrence of cesarean delivery secondary to labor arrest. The secondary outcome was the relationship between the head circumference/obstetrical conjugate ratio and labor duration.

      RESULTS

      A total of 263 women were included. Cesarean delivery for labor arrest was performed in 7.6% (20/263) of the included cases and was associated with more frequent use of epidural analgesia (95.0% vs 45.7%; P<.001), longer second stage of labor (193 [120–240] vs 34.0 [13.8–66.5] minutes; P=.002), shorter obstetrical conjugate (111 [108–114] vs 121 [116–125] mm; P<.001), higher head circumference/obstetrical conjugate ratio (3.2 [3.2–3.35] vs 2.9 [2.8–3.0]; P<.001), and higher birthweight (3678 [3501–3916] vs 3352 [3095–3680] g; P=.003) compared with vaginal delivery. At logistic regression analysis, the head circumference/obstetrical conjugate ratio expressed as Z-score was the only parameter independently associated with risk of cesarean delivery for labor arrest (odds ratio, 8.8; 95% confidence interval, 3.6–21.7) and had higher accuracy in predicting cesarean delivery compared with the accuracy of fetal head circumference and obstetrical conjugate alone, with an area under the curve of 0.91 (95% confidence interval, 81.7–99.5; P<.001). A positive correlation between the head circumference/obstetrical conjugate ratio and length of the second stage of labor was found (Pearson coefficient, 0.16; P=.018).

      CONCLUSION

      Our study, conducted on an unselected low-risk population, demonstrated that the head circumference/obstetrical conjugate ratio is a reliable antenatal predictor of labor arrest leading to cesarean delivery.

      Key words

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