Labour: normal and abnormal
Louise C Kenny, Jenny E Myers in Obstetrics, 2017
The pelvic outlet is bounded anteriorly by the lower margin of the symphysis pubis, laterally by the descending ramus of the pubic bone, the ischial tuberosity and the sacrotuberous ligament, and posteriorly by the last piece of the sacrum. The AP diameter of the pelvic outlet is 13.5 cm and the transverse diameter is 11 cm (Figures 12.3, 12.4). Therefore, the transverse is the widest diameter at the inlet, but at the outlet it is the AP diameter, and the fetal head must rotate from a transverse to an AP position as it passes through the pelvis. Typically, this happens in the midpelvis where the transverse and AP diameters are similar. In addition, the pelvic axis describes an imaginary curved line, a path that the centre of the fetal head must take during its passage through the pelvis, from entry at the inlet, descent and rotation in the midpelvis and exit at the outlet. Recognizing the important features of the maternal pelvis is central to understanding the mechanism of labour.
Pelvis
Harold Ellis, Adrian Kendal Dixon, Bari M. Logan, David J. Bowden in Human Sectional Anatomy, 2017
This midline sagittal T2-weighted magnetic resonace image illustrates many of the important features of the female pelvis. The bony dimensions can be assessed easily. The anteroposterior (AP) diameter of the pelvic inlet (from the superoposterior aspect of the pubic symphysis to the anterior aspect of the promontory on S1) is of key importance for obstetrics; ideally, this should be about 12 cm – the fetal head has a diameter of about 10.5 cm. The AP diameter of the mid-pelvis is usually somewhat larger; this is where rotation of the fetal head occurs during childbirth – much depends on the shape of the sacrum. The AP diameter of the pelvic outlet (from the inferior posterior aspect of the pubic symphysis to the anterior aspect of the lowest fixed point of the sacrum – usually the sacrococcygeal junction) should be similar to that of the inlet or sacrum; only rarely do the common anomalies at this site cause problems during childbirth.
Urogynaecology and pelvic floor problems
Helen Bickerstaff, Louise C Kenny in Gynaecology, 2017
Uterovaginal prolapse is caused by failure of the interaction between the levator ani muscles and the ligaments and fascia that support the pelvic organs. For a detailed description of the relationships and function of these structures, see the review by Wei & De Lancey in Further reading. The levator ani muscles are puborectalis, pubococcygeus and iliococcygeus. They are attached on each side of the pelvic side wall from the pubic ramus anteriorly (pubococcygeus), over the obturator internus fascia to the ischial spine to form a bowl-shaped muscle filling the pelvic outlet and supporting the pelvic organs (see Chapter 1, The development and anatomy of the female sexual organs and pelvis). There is a gap between the fibres of the puborectalis on each side to allow passage of the urethra, vagina and rectum, called the urogenital hiatus. The levator muscles support the pelvic organs and prevent excessive loading of the ligaments and fascia.
Comparing the pelvis of Tibetan and Chinese Han women in rural areas of China: two population-based studies using coarsened exact matching
Published in Journal of Obstetrics and Gynaecology, 2022
Xiaojing Fan, Zhongliang Zhou, Martyn Stewart, Duolao Wang, Xin Lan, Shaonong Dang, Hong Yan
The pelvic dimension including IS, IC, EC and TO was one method used for assessment of contracted pelvis. Whilst this method was easier to implement, it may ignore other parameters. Factors such as gestational weeks, fat thickness and the posture of women when measuring the distance of the two ischial tuberosity’s inside edge may affect the measurements of EC and TO (Laster 1974). Iida et al. suggested that the contracted pelvis should be defined by measures such as the area of the pelvis inlet and the sacral shape (Iida and Takahashi 1993). When standard obstetric measurements were taken and compared to four additional medieval skeletal samples from Sudan, and to modern American standards for the same obstetric dimensions, the Sudanese Kulubnarti pelvis was smaller in most dimensions (Sibley et al. 1992). Studies had illustrated that the accuracy of clinical evaluation of the pelvic outlet is lower than when compared to X-ray pelvimetry, and the parameters of lesser pelvises could be better measured by an ultrasonic (Floberg et al. 1986; Kramarskii and Krasin 1991). Therefore, further assessments of the pelvis of Tibetan women would be required and caution was needed when estimating or comparing the incidence of contracted pelvis in Tibetan women.
Study of the X-Ray Diagnosis of Unstable Pelvic Fracture Displacements in Three-Dimensional Space and its Application in Closed Reduction
Published in Journal of Investigative Surgery, 2019
Chengdi Shi, Leyi Cai, Wei Hu, Junying Sun
One case in this study with pelvic X-ray showed obvious separation of the symphysis pubis, and upper and lower dislocation. Because the posterior ring bone line was blurred and the displacement was not obvious, at another hospital, this was mistaken for vertical upward displacement of the contralateral half pelvis. Thus, lower limb traction was invalid when applied and it failed. After reexamination of the X-rays, CT measurements, and image reconstruction, a Tile C1.1 fracture with pronation displacement was confirmed. The anterior and posterior axial displacements and sagittal rotation displacement were clearly present on pelvic entrance X-rays. The pelvic outlet X-ray clearly showed the sacral foramen and the L5 transverse process, allowing vertical displacement to be distinguished from sagittal plane displacement.
Perineal trauma: incidence and its risk factors
Published in Journal of Obstetrics and Gynaecology, 2019
Masoumeh Abedzadeh-Kalahroudi, Ahmad Talebian, Zohreh Sadat, Elaheh Mesdaghinia
Studies show that about 57% of deliveries without an episiotomy are associated with some degree of perineal laceration (McCandlish 2001; Leal et al. 2014), which is similar to the incidence in our study (50.5%). In our study, the incidence of a perineal laceration was 16%. In Ethiopia (Niguse et al. 2016), the rate of a laceration was 13.2%, and in England, 18.8% (Smith et al. 2013). Another study in Kashan during 2007–2009 also reported a incidence of 16.1% (Mesdaghinia et al. 2011), indicating that the episiotomy rate has not decreased in this city during the recent years. Although the episiotomy is used to increase the pelvic outlet, in the prevention of severe perineal tears, to facilitate of childbirth, and for a shorter foetal expulsion time, it is recommended that it should be limited to the high risk deliveries for severe perineal lacerations, severe dystocia of soft tissue, or need to facilitate a delivery in a compromised foetus. Studies show that tears are usually smaller than an episiotomy, and their recovery is faster and easier (Robinson 2016).
Related Knowledge Centers
- Foramen
- Ischium
- Pelvimetry
- Pubic Arch
- Pelvic Cavity
- Coccyx
- Sacrum
- Ischial Tuberosity
- Pubis
- Ilium