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Morphometric Variations Regarding Age. Correspondence to :. Cesarean sections are excessively indicated in Northen Mexico, using the diagnosis of cephalopelvic disproportion due to a narrow pelvis. Currently, there is no standardized morphometry of the female pelvis in a Mexican population to establish adequate diagnostic parameter. Our study measures the pelvic diameters of the birth canal using abdominopelvic computed tomography CT.
Two hundred and ninety CT from Mexican women between the ages of 18 and 50 were collected and 3D reformatted in order to morphologically measure the pelvic diameters of clinical relevance.
Measurements were conducted by two diagnostic imaging specialists. The mean and standard deviation of the measured diameters were: anatomical conjugate diameter ACD Our study shows that as Mexican women get older, the mean pelvic diameters become narrower. In the last two decades, unjustified cesarean births have increased in Northeastern Mexican middle and high income women Puentes-Rosas et al. Approximately Correct indications for obstetric interventions are essential in order to reduce maternal and perinatal mortality Rozenholc et al.
When these are performed in unnecessary cases, besides the additional costs generated to the health system, it can cause negative effects on the health of the mother and newborn Campero et al. These include complications such as a higher incidence of preterm birth and neonatal death Villar et al.
The indications for a cesarean are: dystocia, previous cesarean section, fetal distress and abnormal presentations Campero et al. There are several types of dystocia, the most common is cephalopelvic disproportion Lenhard et al.
This occurs when there is a discrepancy between the fetal size and the size of the maternal pelvis Korhonen et al. Its diagnosis is crucial in order to determine if the pregnancy should be interrupted surgically and it is carried out by a subjective clinical evaluation which estimates the size of the pelvic cavity through a digital examination of the bony pelvis Cunningham et al. This clinical pelvimetry has been reported to have limited value in identifying women at risk of dystocia Rozenholc et al.
Different imaging studies have been used for pelvimetry to identify the small pelvic diameters, examples include: ultrasound Daghighi et al. CT has been described as the study with the most accurate and reliable picture for high quality pelvimetry Herrmann et al.
In most patients it indicated that a caesarean section for cephalopelvic disproportion, it is not based with a pelvimetry based on an imaging study Santin, The morphometric characteristics of the pelvic cavity are important to be described, so the obstetrician can identify and diagnose cephalopelvic disproportion of a narrow pelvis and correctly indicate a cesarean Santin. The variations in the pelvic parameters of Mexican women have not been reported in the literature, so it is important to compare these with other populations as well as associate any differences regarding age.
The aim of our study was to determine normal values for the anatomic conjugate diameter ACD , the obstetric conjugate diameter OCD , the conjugate diameter diagonal DCD and the interspinous distance ISD using reformatted CT in a Mexican population and determine whether there are significant differences in these parameters regarding age groups.
A sample size with prior calculation of abdominopelvic CT simple or contrasted of Mexican women with an age range between 18 and 50 years mean The studies were conducted between January and June The CT scans were obtained from the Department of Radiology and Imaging database from patients who needed the image study for other purposes.
No patient was radiated for the purposes of this study. The morphometries of the pelvises were performed in the 3D integration work station Centricity RIS-i 4. To better visualize the images a multiplanar reformatting program was used, Volume Rendering software number: 12HW The reconstructed images were then transmitted to the workstation "Advantage Workstation AW 4. Calibration of the workstation was predetermined by the manufacturer.
The reconstruction of the CT did not intervene in any way with the normal protocols of realization, storage and delivery of the study results to the patient or physician requesting the scan. The CT scans were evaluated by two radiologists for compliance with the exclusion criteria. The age of the patients was obtained from the physician's order for the CT. Access to patient's records was not necessary. Table I. Distribution of patients involved in the study according to age ranges.
For each TC, the following morphometry evaluations were performed:. Anatomical conjugate diameter ACD. Distance between the center of the sacral promontory and the upper border of the pubic symphysis Fig. Obstetric conjugate diameter OCD. Distance between the center of the sacral promontory and the posterior border of the symphysis pubis Fig 1b. Conjugate diameter diagonal DCD. Distance between the center of the sacral promontory and the lower border of the symphysis pubis Fig.
Interspinous distance ISD. Distance extending between the medial edge of an ischial spine and the medial border of the contralateral ischial spine Fig. All measurements are reported in centimeters and were stored in a database for subsequent statistical analysis.
Images of the pelvis by three-dimensional reconstruction of a CT scan where the measurement technique anatomic conjugate diameter a , obstetric conjugate diameter b and conjugate diameter diagonal c is observed.
Images of the pelvis by three-dimensional reconstruction of a CT scan where the measurement technique is observed the interspinous diameter.
Statistical analysis. Statistical analysis was obtained using the computer program SPSS version The sample size was determined with a hypothesis test and difference of two means or with one mean as reference value. The mean and standard deviation for each measurement is determined by groups. All results are plotted and included in tables. The ability to replicate measurements is essential for any morphological study, reason why intra- and inter-observer error test were made.
Each scan was measured a second time, two weeks later by the first author. The differences between the two sets of measurements were used in order to calculate a percentage of error intraobserver variability using a Student's pairwise t test for estimating the significance of these results. Finally, in order to assess the interobserver error, a randomized sample of 50 scans was selected and re-measured 2 weeks later by the same person as the first time.
The results were compared in a database with Student's pairwise t test. Ethical considerations. There were no financial or commercial gains in the completion of this study. The authors declare no conflict of interest. The overall mean of each diameter obtained from the samples is shown in Table II. The mean of each diameter divided by age groups is shown in Table III. Table II. Overall morphometric results of the different pelvic diameters in women. A sample of CT scans.
Table III. Morphometric results of the pelvic diameters classified by age group. Table IV. Statistical significant difference in the comparison between the mean results of each diameter between the different age groups. There are few studies in the literature that analyze normal pelvic diameters in the general population Lenhard et al.
More importantly, no study has established a difference in these parameters regarding age. Our study identified that there are significant differences in all these parameters regarding age. As reported in other populations, the OCD varies between Korhonen et al. In the literature there are no data of variations in these diameters according to age.
Our study showed that pelvic diameters narrow with increasing age; women in the group 40 years, presented significantly smaller diameters than other age groups Table III. We recognize that a limitation of this study is that the medical history of each patient involved is unknown. These differences may be related to physiological and endocrine changes, nutritional factors, the amount and intensity of physical activity undertaken by individuals at different stages of life and bone remodelers Morales-Avalos et al.
It is very important to determine the morphometric parameters of the pelvis in our population due to the excess in wrongly indicated cesarean. Knowing these parameters can aid in diagnosing cephalopelvic disproportion and correctly indicate the best type of birth during the different stages of life. We also demonstrated that younger women are more likely to have wider pelvic diameters, which may narrow with increasing age, especially after the age of Table V.
Comparison of results obtained from studies of different populations in morphometric pelvic parameters. Alijahan, R. Diagnostic accuracy of maternal anthropometric measurements as predictors for dystocia in nulliparous women.
Midwifery Res. Campero, L. Trends in caesarean sections associated with non-clinical factors in a Birthing Educational Center in Mexico City. Salud Publica Mex. Cesarean-associated complications: the importance of a scarcely justified use. Cunningham, F. Williams Obstetrics. New York, McGraw-Hill, Daghighi, M. Association between obstetric conjugate diameter measured by transabdominal ultrasonography during pregnancy and the type of delivery.