Humerospinous distance measurements: accuracy and usefulness for predicting shoulder dystocia in delivery at term.

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To investigate if the humerospinous distance, as an indicator of shoulder width, could predict shoulder dystocia at term. Prospective cross-sectional study of a stratified reference group of healthy women and a test group of women with risk factors for shoulder dystocia. Measurements were not revealed. Outcome measures were difficulties with delivery of the shoulders and correlation with maternal body mass and birth weight. Seventy-two women with singleton pregnancies at a University Clinic: 32 women at 39-42 weeks for reference and 40 women in an at-risk test group (weight > 90 kg, weight gain > 20 kg, previous macrosomic baby, history of shoulder dystocia/difficult delivery, clinical suspicion of a large baby). Women with a breech fetus, twins and those not able to deliver vaginally were excluded. Fetal shoulders were measured from the convergence of the cervical spinous processes at the approximate cervicothoracic vertebral junction to the medial border of the humeral head. Correlations were made with maternal body mass, birth weight, birth weight estimation, ultrasound and postnatal humerospinous measurements. One case of shoulder dystocia in a fetus with an average humerospinous measurement occurred in the reference group and there were no cases in the test group. There was no predictive value of a large humerospinous measurement and no correlation with maternal or fetal size. Movement of the fetal arm could change the humerospinous distance considerably, which could account for the difference between a normal and large measurement. The humerospinous distance cannot be used to predict shoulder dystocia.