Computed Tomography Pelvimetry Research Articles

Updating of pelvimetry standards in modern obstetrics

Clinical value of pelvimetry in modern obstetrics practices has never been established and normal values are set since the middle of the twentieth century. The aim of this study was to describe current dimensions of pelvis in a female French Caucasian population. A retrospective, bi-centric observational study was conducted from August 2013 to August 2019 in two French departments of Obstetrics. We included all Caucasian women who had a computed tomography pelvimetry during pregnancy. The primary outcome was the values of the obstetric transverse diameter, obstetric conjugate diameter and bispinous diameter. Five hundred and fifty-one CT pelvimetries were analyzed. The median Obstetric Transverse Diameter (OTD) was 12.41 cm and the 3rd percentile was 11 cm. The median Obstetric Conjugate Diameter (OCD) was 12.2 cm and the 3rd percentile was 10.5 cm. The median Bispinous Diameter (BSD) in our data collection was 10.9 cm and the 3rd percentile was 9.3 cm. A significant correlation coefficient between women’s height and OTD, OCD and BSD was found. In our study, the OCD and the BSD have not evolved since the middle of the twentieth century. The obstetric transverse diameter was smaller than the standard currently used.

Internal Versus External Pelvimetry: A Validation Study With Clinical Implications

INTRODUCTION:Investigating the correlations between external pelvimetry variables and actual birth canal dimensions has important implications for clinical practice, especially for predicting dystocia. This validation study tests external and internal pelvimetry correlations.METHODS:This single-centered retrospective study included 142 women with records of computed tomography pelvimetry. The correlations between four internal variables (obstetric conjugate, transverse diameters of inlet, midplane, and outlet) and five external variables (intertrochanteric, inter anterosuperior iliac spines, external conjugate, transverse diagonal, and prepubic) were first studied individually. Then, the correlations between each internal variable and the seven external variables were jointly evaluated after adjusting for body mass index.RESULTS:As expected, the external conjugate correlated with the obstetric conjugate (r= .65;p< .01) but only weakly with the transverse outlet (r= .21;p< .05). In the simple correlation analysis, the intertrochanteric measure is also correlated with the transverse inlet (TRi), midplane (TRm), and outlet (TRo;r =.542–.672). The transverse diagonal measure marginally correlated with the TRi (r= .29;p< .01). In the multiple regression models, the intertrochanteric measure is associated with the TRi, TRm, and TRo, while the transverse diagonal is associated with the TRi (B= .27;p= .01). The prepubic diameter was not a predictor of birth canal dimensions in either simple or multiple regression models.CONCLUSION:Our study confirms that the reduction of the birth canal in some dimensions (i.e., obstetric conjugate and transverse diameters) is predictable with external, accessible pelvic diameters (e.g., external conjugate, transverse diagonal, and intertrochanteric).

Evaluation of fetal dose during pelvimetry CT scan procedure by Monte Carlo using GATE

Pelvimetry is performed at the late pregnancy to measure the size of the pelvis through its different diameters in order to determine the possible modalities of delivery: by natural way or by programmed cesarean section. When a pregnant woman undergoes a radiological examination, the risk associated with radiation exposure is of concern. In general, the fetal dose cannot be measured directly, so Monte Carlo (MC) methods are used for this purpose. Therefore the objective of this study is to evaluate the fetal dose during a Computed Tomography (CT) pelvimetry examination by means of a MC method using Geant4 Application for Tomographic Emission code (GATE). A simulation of a CT pelvimetry examination was performed by modeling a Hitachi Supria 16-slice scanner that follows a CT pelvimetry protocol. A 16-diameter phantom is used to model the fetus inside a 32-diameter phantom that represents the patient's body. The fetal dose in this simulation was 0.95 mGy. Other studies on fetal dose from pelvic CT scans found that it does not exceed a few mGys, which is not a real concern. On another hand, the dose showed a dependence on the variation of the tube current and also the voltage. Therefore, these parameters can be used as a basis for action to reduce exposure and limit risk during such examinations.

Obstetric pelvimetry by three-dimensional computed tomography in non-pregnant Japanese women: a retrospective single-center study

Objective While a basic understanding of pelvic size and typology is still important for obstetricians, pelvic measurement data for Japanese women are very scarce. To our best knowledge, no large-scale pelvimetry studies of Japanese women have been made for the past 50 years. This study aimed to investigate the accurate size, particularly the obstetric conjugate (OC) and transverse diameter of the pelvic inlet (TD), of modern Japanese women, using three-dimensional (3D) computed tomography (CT), and to obtain their reference values. Methods This retrospective, single-center observational study enrolled Japanese non-pregnant women aged between 20 and 40 years, who underwent pelvic CT examination from 2016 to 2021. CT was performed for various reasons, including acute abdomen, search for cancer metastases, and follow-up of existing disease. However, no cases were taken for pelvic measurements. Pelvimetry was performed retrospectively using a 3D workstation. The OC was measured on a strict lateral view and the TD was measured on an axial-oblique view. Other clinical data, such as age, height, and weight, were also extracted from the medical charts and analyzed. Results A total of 1,263 patients were enrolled, with the mean age of 32.7 years (standard deviation [SD] 6.2). The mean height, weight, and body mass index were 158.8 cm (SD 5.8), 54.8 kg (SD 11.7), and 21.7 kg/m2 (SD 4.4), respectively. The mean OC length was 127.0 mm (SD 9.5, 95% confidence interval [CI] 126.5–127.5), while the mean TD length was 126.8 mm (SD 7.5, 95% CI 126.4–127.2). Both values were normally distributed. Height was significantly associated with OC (regression coefficient = 0.75 [95% CI 0.66–0.84], p < .001) and TD (regression coefficient = 0.63 [95% CI 0.56–0.70], p < .001). Age showed a weak but statistically significant positive association with TD (regression coefficient = 0.14 [95% CI 0.07–0.20], p < .001) and OC (regression coefficient = −0.10 [95% CI −0.18 to −0.01], p = .026). Conclusion The 3D CT pelvimetry in 1,263 non-pregnant Japanese women of childbearing age revealed the mean OC and TD of 127.0 mm, and 126.8 mm, which were 11.8 mm and 4.3 mm larger, respectively, than those in the survey in 1972. Our data will be referred to in clinical practice as the standard pelvic measurement values for the Japanese population.

Can CT Pelvimetry Be Used to Predict Circumferential Resection Margin Positivity in Laparoscopic Resection of Middle and Lower Rectum Cancer?

Background Previous studies have shown that pelvimetry can be valuable in predicting surgical difficulties in rectal cancer operations. However, its usability in predicting circumferential resection margin (CRM) involvement remains debatable. This study investigated the factors affecting CRM status and the importance of computed tomography (CT) pelvimetry in predicting CRM involvement in laparoscopic resection of middle and lower rectal cancer. Methodology In this study, we retrospectively investigated the data of 111 patients who underwent a laparoscopic operation for middle and lower rectum cancer at Ankara University Faculty of Medicine, Department of Surgical Oncology between January 2014 and January 2020. The predictive value of CT pelvimetry and other variables on the CRM statuswas analyzed. Results The following four pelvic parameters differed significantly between the genders: transverse diameter of the pelvic inlet (p = 0.024), anteroposterior diameter of the pelvic outlet (p = 0.003), transverse diameter of the pelvic outlet (p < 0.001), and pelvic depth (p < 0.001). The effect of pelvic anatomic parameters on CRM involvement was not found to be significant. It was found that tumor height from the anal verge (p = 0.004), tumor size (p < 0.001), and gender (p = 0.033) were significant risk factors for CRM involvement. Survival was poor in patients with male gender (p = 0.032), perineural invasion (p < 0.001), and grade 3 tumor. Conclusions In this study, no benefit was found in predicting CRM positivity from CT pelvimetry in the laparoscopic resection of middle and lower rectal cancer. Besides, tumor height from the anal verge, tumor size, and gender were important factors for CRM positivity. Although our study sheds light on this issue, prospective randomized studies with larger sample sizes are needed.

A possible prediction of dystocia at the time of cesarean delivery: Gluteal muscle contracture, a single center experience from China.

The study assessed the pelvic dimensions by computed tomography (CT) performed for gluteal muscle contracture women, and evaluated the impact of malformations on several essential obstetric parameters.The CT pelvimetry was retrospectively performed in 25 gluteal muscle contracture women selected consecutively whether they had delivery history or not. Among the pelvic inlet plane, the mid plane and the outlet plane, 12 indicators including the transverse diameter of the pelvic inlet, the conjugate vera, the diagonal conjugate, the biischial diameter, the anteroposterior diameter of the middle pelvis, transverse outlet, the posterior sagittal diameter of outlet, the conjugate of the outlet, the anterior sagittal diameter of the outlet, the curvature and length of the sacrum, the angle of pubic arch were collected.Finally, the mean age of these women was 26.6 ± 5.0 years. Most pelvises had anteroposterior elliptical appearance in inlet and size of the female pelvis. The most statistically different and most clinically significant indicator was the biischial diameter, gluteal muscle contracture women were 95.6 ± 9.3 mm and the normal women from other study were 105.0 ± 7.9 mm, the comparison showed a significant difference (P < .001).Generally, most gluteal muscle contracture women had features of anthropoid pelvis which were quite different from normal Chinese female. These results may serve as a basis for future studies to assess its utility and prognostic value for a safe vaginal delivery in gluteal muscle contracture women.

Development of CT Pelvimetry Using Deep Learning Based Reconstruction

X-ray pelvimetry is typically performed for the diagnosis of the cephalopelvic disproportion (CPD). The purpose of this study was to assess the utility of new computed tomography (CT) reconstruction "deep learning based reconstruction (DLR) " in ultra-low dose CT pelvimetry. CT pelvimetry was performed 320-row CT. All CT images were reconstructed with and without DLR and transferred for workstation to processing martius and guthmann view. Radiologist and obstetrician-gynecologist subjectively ranked overall image quality of each CT image from the best to the worst. Exposure dose of the CT pelvimetry used a following calculated value, displayed CT dose index (CTDI) vol multiplied by measured value using the thimble chamber and pelvic phantom, and of the X-ray pelvimetry used Japan-Diagnositic Refernce Levels 2015 as a reference, were compared. 3D images obtained from CT pelvimetry with DLR showed accurate biparietal diameter and obstetric conjugate as compared to without DLR. Radiation dose of CT pelvimetry is 0.39 mGy, of X-ray pelvimetry is 1.18 mGy, respectively. Conculusion: Although the visualizing high contrast object, such as bone morphology, is likely to reduce exposure dose in CT examination generally, DLR enable to further dose reduction to keep image quality. 3D image processing from CT pelvimetry solves the problem of expansion rate in X-P pelvimetry and provide accurate measurements. Furthermore, CT pelvimetry can undergo more comfortable position for Pregnant Woman in Labor.

Intra- and inter-rater reliability in a comparative study of cross-sectional and spiral computed tomography pelvimetry methods.

BackgroundDifferent low-dose computed tomography (CT) pelvimetry methods can be used to evaluate the size of birth canal before delivery. CT pelvimetry might generate an acceptable low fetal radiation dose but its measurement accuracy is unknown.PurposeTo investigate intra- and inter-rater measurement reliability of cross-sectional and two spiral CT pelvimetry methods: standard spiral and short spiral.Material and MethodsTen individuals (age ≥60 years, body mass index ≥30 kg/m2) having a CT scan of the abdomen also had CT pelvimetry scans. Three radiologists made independent measurements of each pelvimetry method on two occasions and also in consensus for a reference pelvimetry computed from the standard-dose CT scan of the abdomen. Inter- and intra-rater reliability was analyzed by intraclass correlation coefficient.ResultsMeasurements in the short spiral pelvimetry demonstrated excellent intra- and inter-rater reliability, intraclass correlation coefficient ≥0.93, and good to excellent 95% confidence interval 0.87–0.99. Corresponding results of the standard spiral and cross-sectional pelvimetry showed good to excellent intraclass correlation coefficient ≥0.85 and ≥0.76, and 95% confidence interval was least good and moderate 0.73–0.98 and 0.59–0.97, respectively. Intraclass correlation coefficient between reference pelvimetry and other CT methods showed analogous results.ConclusionThe short spiral pelvimetry demonstrated high and best reliability in comparison to other methods. Standard spiral method showed also good measurement reliability but the short spiral pelvimetry generates lower fetal radiation dose. This method might be suitable for measurements at narrow pelvis. Patient acceptance and attitude to CT pelvimetry should be investigated.

49 Performance Assessment of Magnetic Resonance Imaging (MRI) pelvimetry using ex vivo anatomic pieces and a 3D-printed geometric-distortion phantom

Introduction Feto-maternal morbidity and mortality increase with prolonged labor which can be related with fetalpelvic disproportion. Pelvimetric imaging is useful for assessing the eligibility of vaginal delivery in patients suspected of having disproportion [1] . Commonly performed using Computed Tomography (CT), pelvimetry is being increasingly done in MRI in order to tackle issues of ionizing-radiation exposure and take advantage of the rich contrast provided in MRI [2] . Nonetheless, MR images can be subjected to geometric distortions because of hardware design limitations [3] . Such distortions may impair MRIpelvimetric measurements. In this study, we assessed the accuracy of MRI-pelvimetry compared with CTpelvimetry using ex-vivo pelvises and a 3D-printed geometric-distortion phantom. Method We scanned ten ex-vivo pelvises on a CT scanner (Siemens Sensation) using the implemented clinical low-dose (LD-CT) and high-dose (HD-CT) pelvimetry protocol. MRI was performed on four 1.5T MRI scanners (Siemens Avanto, GE Signa, Philips Achieva, Toshiba Elan). Pelvises were scanned in sagittal and oblique axial using T1-, T2-weighted FSE and T1-weighted SPGR sequences. A trained radiologist performed pelvimetry measurements. Pelvic inlet and outlet anteroposterior diameters were measured using sagittal images. Pelvic inlet and outlet transverse diameters were measured using oblique axial images. For data analysis, MRI measurements were compared with CT using Bland-Altman plots and discrepancy analysis. MRI measurements were also analyzed for inter-scanner variability. Geometric distortion (GD) measurement: we used a custom previously-published methodology which relies on a 3D-printed phantom made up of 3621 control points which are 5 mm-diameter spheres equally spaced within a cylinder (diameter = length = 170 mm) [4] . GD images were acquired on the Siemens Avanto MR unit with and without the manufacturer’s correction that is available but commonly unused by clinical teams. Results The discrepancy between LD-CT and HD-CT measurements was up to 10%. The discrepancy between MRI and LD-CT was up to 11%. As for MRI and HD-CT, the discrepancy was up to 7%. MRI inter-scanner variation was up to 8%. As for geometric distortions, measurements were −1.4 mm Conclusion For pelvimetry purposes, our preliminary results show that MRI is as much accurate as high-dose CT and outperforms low-dose CT. We also show that geometric distortions can be minimized in MR images by using the implemented corrections. Hence MRI pelvimetry appears as an excellent alternative to CT pelvimetry in an endeavor to reduce fetuses exposure to ionizing radiation. Upcoming works in this study include assessment of interobserver reproducibility with the intervention of a second radiologist and geometric distortion measurement on the three remaining MRI scanners.

Computed tomographic pelvimetry in English bulldogs

English bulldogs have been reported to have a high incidence of dystocia and caesarean section is often performed electively in this breed. A narrow pelvic canal is the major maternal factor contributing to obstructive dystocia. The objective of this cross-sectional study was to assess the pelvic dimensions of 40 clinically healthy English bulldogs using computed tomography pelvimetry. A control group consisting of 30 non-brachycephalic dogs that underwent pelvic computed tomography was retrospectively collected from the patient archive system. Univariate analysis of variance was used to compare computed tomography pelvimetry of both groups and the effects of weight and gender on the measurements. In addition, ratios were obtained to address pelvic shape differences. A significantly (P = 0.00) smaller pelvic size was found in English bulldogs compared to the control group for all computed tomography measurements: width and length of the pelvis, pelvic inlet and caudal pelvic aperture. The pelvic conformation was significantly different between the groups, English bulldogs had an overall shorter pelvis and pelvic canal and a narrower pelvic outlet. Weight had a significant effect on all measurements whereas gender that only had a significant effect on some (4/11) pelvic dimensions. Our findings prove that English bulldogs have a generally reduced pelvic size as well as a shorter pelvis and narrower pelvic outlet when compared to non-brachycephalic breeds. We suggest that some of our measurements may serve as a baseline for pelvic dimensions in English bulldogs and may be useful for future studies on dystocia in this breed.

Age-related trends of lesser pelvic architecture in females and males: a computed tomography pelvimetry study.

The pelvis and the spine form a system balancing human skeleton. Within this system, the pelvis adapts to age-related changes in the spine. Previous studies were predominantly focused on changes of pelvic parameters in the sagittal plane. The aim of this study was to reveal age-related changes of lesser pelvic dimensions at different levels of the pelvic cavity in the sagittal and coronal planes and to explore sexual dimorphism in age-related tendencies. The computed tomography pelvimetry was performed on the three-dimensional workstation. The research sample included 211 females aged 18 to 84 years and 181 males aged 18 to 82 years, who underwent an examination at the Riga East University Hospital, Clinical Center “Gailezers,” Latvia. Three pelvic angles and transverse and sagittal diameters of the lesser pelvis were measured at four levels: the inlet, two axial planes in the mid-cavity, and the outlet. The results demonstrated that more pronounced age-related changes occurred in the inlet and the outlet of the lesser pelvis. The mid-cavity was less changing. The transverse diameter between acetabular centers and the sagittal diameter at the level of ischial spines were independent of age. In general, the common age-related trends were observed for pelvic parameters in females and males. A single exception was the proportion of diameters at the level of ischial spines, which decreased in males only. For parameters associated with pelvic floor diseases, age-related changes occurred in the direction of pathology.

Computed tomography pelvimetry as a predictor of technical difficulty in total mesorectal excision

To investigate the limiting effect of pelvic diameters on the technical difficulty of total mesorectal excision(TME) for rectal cancer by computed tomography pelvimetry. From January 2009 to January 2011, 69 patients with rectal cancer underwent TME in the Department of Proctology at the Changhai Hospital in Shanghai. There were 55 males and 14 females. Using three dimensional reconstruction software, pelvic dimensions of rectal cancer patients were measured based on pelvic MDCT thin-slice computed tomography. All the patients were measured for 15 pelvic parameters, including the length of pelvic inlet, the length of pubic symphysis, the interspinous distance, the distance from sacral promontory to tip of coccyx, etc. All the procedures were open surgery, including anterior resection(n=19), low anterior resection and ileostomy(n=29) and abdominal perineal resection(n=21). Duration of the operation and blood loss at surgery were recorded as evaluation indicators of the technical difficulty of total mesorectal excision. By univariate analysis significant pelvic parameters were selected. Multiple regression analysis was used to investigate the relationship between pelvic parameters and blood loss or duration of operation. The mean operative time was(139.9±32.4) min and the mean intraoperative blood loss was (228.8±150.6) ml. Multivariate analysis showed that the interspinous distance, the length of pelvic inlet, the distance from sacral promontory to the tip of coccyx were the main factors affecting the operation time, and that the length of pubic symphysis and the distance from sacral promontory to the tip of coccyx were the main factors affecting the amount of blood loss (all P<0.05). Among the 3 procedures, the multivariate analysis for low anterior resection appeared to be most valuable, in which operative time was associated with the distance from sacral promontory to the tip of coccyx and the interspinous distance (adjusted coefficient of determination of the regression equation, Rc(2)=0.460, P=0.003). Factors associated with intraoperative blood loss were the length of pelvic inlet, the distance from sacral promontory to the tip of coccyx, and the sacrum-pubis angle(Rc(2)=0.358, P=0.022). Comprehensive analysis of the measurement parameters showed that the ratio between the length of pelvic inlet and the distance from sacral promontory to the tip of coccyx was associated with the operative time and blood loss. This ratio was significantly higher in female patients than that in males. In females with a ratio greater than 1, the operative time was significantly shorter(P=0.050), and the intraoperative blood loss was significantly less in males with a ratio greater than 0.9(P=0.021). Operative time and intraoperative blood loss for total mesorectal excision are more favorable in patients with a wide and shadow pelvis. Surgical difficulty is increased in deep and narrow pelvis or those with major sacrum curvature. The difficulty of total mesorectal excision procedure can be predicted by measuring the length of pelvic inlet and the distance from sacral promontory to the tip of coccyx.

Three-dimensional pelvimetry by computed tomography

This study was undertaken to assess the agreement of computed tomography (CT) pelvimetry with different postprocessing techniques. CT data sets of 25 patients were retrospectively analysed. There were no CT examinations performed solely for pelvimetry, and there was no radiation exposure for study purposes. Six pelvimetric measurements were obtained by two independent observers in four data sets of each patient, i.e. on biplanar topograms, multiplanar reconstructions of 1-mm slices, volume-rendered images of the same data and volume-rendered images based on 5-mm-thick images. Interobserver agreement and variability were determined by Bland-Altman analysis. A human skeleton was also scanned and measured with the same techniques and by ruler as reference. With a correlation coefficient of 0.98, interobserver agreement was best for assessing 3D volume-rendered images reconstructed from 1-mm-thick slices. Interobserver variability was very good for sagittal outlet and midpelvic diameter, transverse inlet diameter and obstetric conjugate (correlation coefficients 0.96-0.99) but limited for intertuberous and interspinous distance. CT and ruler measurements of the skeleton showed excellent agreement. Pelvimetry can be obtained with low interobserver variability on 3D volume-rendered CT reconstructions. Thus, CT pelvimetry is suitable to gain exact knowledge of pelvic anatomy to identify relevant parameters for dystocia in retrospective studies.

Guidelines for Computed Tomography and Magnetic Resonance Imaging Use During Pregnancy and Lactation

There has been a substantial increase in the use of computed tomography (CT) and magnetic resonance imaging (MRI) in pregnancy and lactation. Among some physicians and patients, however, there are misperceptions regarding risks, safety, and appropriate use of these modalities in pregnancy. We have developed a set of evidence-based guidelines for the use of CT, MRI, and contrast media during pregnancy for selected indications including suspected acute appendicitis, pulmonary embolism, renal colic, trauma, and cephalopelvic disproportion. Ultrasonography is the initial modality of choice for suspected appendicitis, but if the ultrasound examination is negative, MRI or CT can be obtained. Computed tomography should be the initial diagnostic imaging modality for suspected pulmonary embolism. Ultrasonography should be the initial study of choice for suspected renal colic. Ultrasonography can be the initial imaging evaluation for trauma, but CT should be performed if serious injury is suspected. Pelvimetry now is used rarely for suspected cephalopelvic disproportion, but when required, low-dose CT pelvimetry can be performed with minimal risk. Although iodinated contrast seems safe to use in pregnancy, intravenous gadolinium is contraindicated and should be used only when absolutely essential. It seems to be safe to continue breast-feeding immediately after receiving iodinated contrast or gadolinium. Although teratogenesis is not a major concern after exposure to prenatal diagnostic radiation, carcinogenesis is a potential risk. When used appropriately, CT and MRI can be valuable tools in imaging pregnant and lactating women; risks and benefits always should be considered and discussed with patients.

Intrinsic measurement bias on computed tomography scout view is unpredictable: Computed tomography pelvimetry using a phantom

Our aim was to determine the degree of bias in CT scanogram measurements. We obtained standard lateral and anteroposterior (AP) pelvimetry scanograms of a phantom pelvis after placing ball bearings or aluminium rods to mark bony landmarks. Computed tomography pelvimetry was carried out at the manufacturer-recommended table height on two commercial CT scanners and at 10-mm increments up to 50 mm above and below this height. The AP inlet, AP outlet, interspinous distance and transverse diameters were each measured three times for each scanogram. The true measurements were obtained directly from the disassembled phantom. Bias was defined as the difference between the CT measurement and the true measurement. Observer error was negligible. The transverse diameter was overestimated at high table positions and underestimated at low table positions on both scanners (+6 to -10 mm). After correcting for geometric distortion, up to 6 mm bias was still present. The point at which no bias occurred was different for each scanner and did not correspond to the manufacturers' recommended table height. The outlet was overestimated on both scanners by up to 5 mm. The true inlet measurement was overestimated by 1.2 mm. The interspinous distance was minimally underestimated on both scanners. The measurements on CT scanogram were underestimated or overestimated in an inconsistent and unpredictable fashion, varying from one type of measurement to another and from CT scanner to CT scanner. This has implications for the accuracy and clinical utility of measurements obtained from a CT scanogram.

Measurement error in computed tomography pelvimetry

Computed tomography pelvimetry is still used in clinical practice. We wished to quantify observer error in order to assess the level of confidence with which pelvic measurements can be described as adequate or inadequate. Anteroposterior inlet, anteroposterior outlet, transverse inlet and interspinous distances were measured from 11 CT pelvimetry examinations by five observers at one institution. Three CT pelvimetries were measured by five observers at a second institution. Intraobserver and interobserver variation was assessed using analysis of variance. Reliability of measurements was assessed using intraclass correlation coefficient. Combined error was calculated to determine 95% confidence limits for published minimum recommended pelvic measurements. The standard error of measurement, combining all sources, for measurement of the bony dimensions of the pelvis were: for anteroposterior inlet, 2.0 mm; anteroposterior outlet, 6.9 mm; transverse inlet, 1.3 mm; and interspinous distance, 2.1 mm. The 95% confidence interval around the recommended anteroposterior outlet of 100 mm was 88.5-111.3 mm. Observer variation in measurement of anteroposterior outlet is so large as to make the measurement of doubtful clinical utility.

An appraisal of computed tomography pelvimetry in patients with previous caesarean section

This study was conducted to determine the value of computed tomography (CT) pelvimetry in patients with previous caesarean section. Of 219 pregnant women with one previous caesarean section, 100 had antenatal CT pelvimetry and a control group of 119 women had no CT pelvimetry. In the CT pelvimetry group, 51.0% delivered by caesarean section, 28.0% underwent elective caesarean section for contracted pelvis based on the findings of CT pelvimetry and 23% underwent emergency caesarean section after a trial labour. In the control group, 21.8% underwent emergency caesarean section. The differences in birth weight and Apgar scores between the groups were not statistically significant. CT pelvimetry increased the rate of caesarean delivery, suggesting that CT pelvimetry before a vaginal birth after a previous caesarean delivery is of limited value.

Computed tomography comparison of bony pelvis dimensions between women with and without genital prolapse

Objective: To compare bony pelvis dimensions between white women with and without genital prolapse using computed tomography (CT) pelvimetry. Methods: Thirty-four multiparous white women with vaginal prolapse beyond the hymen and 34 matched white controls with no signs or symptoms of pelvic support defects underwent CT pelvimetry. The anteroposterior and transverse diameters of the pelvic inlet, the interspinous diameter of the midpelvis, and the intertuberous diameter of the pelvic outlet were measured. Post hoc power analysis showed that 22 women were needed in each group to detect a 10% difference in the pelvic dimensions between groups, with an α error of 1% and a β error of 10%, resulting in a 90% power. Results: Mean (± standard deviation [SD]) age of the subjects was 63.4 ± 8.3 years, compared with 62.9 ± 7.8 years for controls. Mean parity of the subjects was 3.3 ± 1.7, compared with 3.6 ± 1.7 for controls. Mean (± SD) anteroposterior (12.5 ± 1.3 versus 12.8 ± 1.0 cm), interspinous (11.5 ± 0.8 versus 11.2 ± 0.9 cm), and intertuberous (10.0 ± 1.0 versus 9.8 ± 0.8 cm) diameters were not significantly different between study groups. Mean transverse diameter of the pelvic inlet was significantly greater in women with prolapse than those without prolapse (12.9 ± 0.7 versus 12.4 ± 0.6 cm, P = .006). Conclusion: Women with advanced vaginal prolapse have larger transverse inlet diameters than do women with normal pelvic support.

Trends in the use of pelvimetry techniques

Assessment of maternal pelvic dimensions is usually considered necessary where vaginal delivery is contemplated in a breech presentation or if reduced pelvic dimensions are suspected in a current or previous pregnancy. Pelvimetry techniques include computed tomography (CT), conventional radiography, digital fluorography and magnetic resonance imaging (MRI). The first three techniques result in a radiation dose to mother and fetus which, depending on how the technique is performed, can vary by up to 40-fold. Of the techniques using X-rays, CT pelvimetry with a lateral scanogram generally gives the lowest radiation dose and conventional radiography using an air gap technique with a single lateral view is a relatively low-dose alternative where CT is not available. A questionnaire was sent to 227 hospitals during 1993 and 1996 to assess whether there was a move towards lower dose techniques of pelvimetry. The results show a trend away from conventional pelvimetry (48.4% in 1993 to 28% in 1996) with a small proportion of centres using MRI (4%) in 1996. Of the centres still using conventional pelvimetry, relatively few were using a low-dose air-gap technique (2.1% in 1993 to 10.9% in 1996). An increasing majority of centres were using one-view CT (69.3% in 1993 and 80.4% in 1996) but a significant proportion were still performing more than one view. This study shows that there was a move towards lower dose techniques of pelvimetry but that there were still many hospitals that had not implemented a policy of reducing radiation exposure in these patients.

Value of Computed Tomography Pelvimetry in Patients with a Previous Cesarean Section

A case-control study was conducted at the Department of Obstetrics and Gynaecology, King Abdulaziz University Hospital, Jeddah, Saudi Arabia, to determine the value of computed tomography pelvimetry in patients with a previous cesarean section. Between January 1993 and December 1995, 219 pregnant women with one previous cesarean section met the criteria for vaginal birth after cesarean delivery. One hundred women had antenatal CT pelvimetry for assessment of the pelvis. One hundred and nineteen women did not have CT pelvimetry and served as control. Fifty-one women (51%) in the CT pelvimetry group delivered by cesarean section. Twenty-three women (23%) underwent elective cesarean section for contracted pelvis based upon the findings of CT pelvimetry and 28 women (28%) underwent emergency cesarean section after trial of labor. In the group who did not have CT pelvimetry, 26 women (21.8%) underwent emergency cesarean section. This was a statistically significant difference (P=0.02). There were no statistically significant differences in birthweight and Apgar scores in either group. There was no perinatal or maternal mortality in this study. Computed tomography pelvimetry increased the rate of cesarean delivery without any benefit in the immediate delivery outcomes. Therefore, the practice of documenting the adequacy of the pelvis by CT pelvimetry before vaginal birth after cesarean should be abandoned.