Masteling Mariana, DeLancey John O L, Ashton-Miller James A
Department of Mechanical Engineering, University of Michigan, 2350 Hayward St, Ann Arbor, MI 48109, United States; Department of Biomedical Engineering, University of Michigan, 200 Bonisteel Blvd, Ann Arbor, MI 48109, United States.
Department of Obstetrics and Gynecology, University of Michigan, 1540 E Hospital Dr, Ann Arbor, MI 48109, United States.
Clin Biomech (Bristol). 2025 Feb;122:106430. doi: 10.1016/j.clinbiomech.2025.106430. Epub 2025 Jan 11.
The lower birth canal is the final constriction through which a fetal head must pass for delivery. Unfortunately, injuries to the lower birth canal tissues occur in up to 19 % of first-time vaginal deliveries due to the 300 % stretch required.
This is a secondary analysis of data from 56 healthy nullipara recorded by a lower birth canal dilator during the first stage of labor. A four parameter Fractional Zener rheological Model was used to characterize the canal viscoelastic properties during the first stage of labor. We tested the (null) hypothesis that the Model constants identified during the initial 20 s ramp-and-5-min-hold dilation from 40 to 55 mm will not accurately predict the final hoop tension after 60 min of slower dilation.
The null hypothesis was rejected in that when the four Model parameters were calculated for all nullipara from the 20-s-ramp-and-5-min-hold data, the relative fit error was 8 ± 4 %, and the relative prediction error after 60 min of dilation was 10 ± 5 %. Furthermore, when the Model constants were instead calculated from the 20 s ramp and only the initial 90 s of the 5-min-hold, the error was still acceptable: 13 ± 4 % for relative fit and 13 ± 18 % for relative prediction.
Two minutes is sufficient to characterize canal viscoelastic properties during the first stage of labor and identify those with stiffer tissues at higher risk for a pelvic floor injury during delivery. This could form the basis for a clinical test predicting injury.
产道下段是胎儿头部娩出时必经的最后一道狭窄通道。遗憾的是，由于需要扩张300%，首次阴道分娩中高达19%会出现产道下段组织损伤。
这是一项对56名健康初产妇在第一产程中由产道下段扩张器记录的数据进行的二次分析。采用四参数分数阶齐纳流变模型来表征第一产程中产道的粘弹性特性。我们检验了这样一个（零）假设：在最初20秒斜坡式加5分钟保持扩张从40毫米至55毫米过程中确定的模型常数，无法准确预测60分钟较慢扩张后的最终环向张力。
零假设被拒绝，因为当根据20秒斜坡式加5分钟保持的数据计算所有初产妇的四个模型参数时，相对拟合误差为8±4%，60分钟扩张后的相对预测误差为10±5%。此外，当模型常数改为根据20秒斜坡式加5分钟保持中仅最初90秒的数据计算时，误差仍然可以接受：相对拟合误差为13±4%，相对预测误差为13±18%。
两分钟足以表征第一产程中产道的粘弹性特性，并识别出组织较硬、分娩时盆底损伤风险较高的产妇。这可为预测损伤的临床试验奠定基础。
