Diagnostic Value of Clinical Pelvimetry and Sonopelvimetry in Determining Mode of Delivery in Nulliparous Women

Abstract

Background:

Normal morphological features of the maternal pelvis are important prerequisites for vaginal delivery. Clinical pelvimetry and sonopelvimetry are inexpensive methods of assessing pelvic capacity. This study aims to determine the diagnostic accuracy of clinical pelvimetry and sonopelvimetry in predicting the mode of delivery in nulliparous women.

Materials and Methods:

In this cross-sectional study, 210 nulliparous women who came for delivery were assessed regarding their clinical and trans-abdominal ultrasonographic pelvimetry characteristics. Parameters including sacral promontory, diagonal conjugate diameter, curvature of the sacrum, interspinous diameter, side walls, sacrosciatic notch, and sub-pubic arch, prominence of coccyx, and intertubberous diameter were evaluated through clinical pelvimetry. Sonopelvimetry was performed to determine diagonal conjugate diameter. The measurements were compared between those who delivered through the vaginal route versus cesarean section (C/S). The receiver operating curve was depicted to determine the value of pelvimetry to prognosticate delivery mode.

Results:

Sacral promontory, diagonal conjugate diameter, curvature of the sacrum, interspinous diameter, side walls, sacrosciatic notch, sub-pubic arch, prominence of coccyx, and inter tuberous diameter were insignificantly different between those who delivered through the vaginal route versus C/S (P > 0.05). The mean diagonal conjugate diameter in ultrasonography assessments was 119.29 ± 7.80 mm in those undergoing C/S versus 120.12 ± 8.72 mm for NVD ones (P value = 0.659). None of the pelvic inlet, mid-pelvic, and outlet parameters could statistically predict the probability of CPD (P value > 0.05).

Conclusion:

Based on the findings of this study, neither clinical pelvimetric parameters nor trans-abdominal ultrasonography could appropriately prognosticate delivery appropriateness through the vaginal route.

INTRODUCTION

Labor abnormality is defined as when the presenting part of the fetus cannot progressively enter into the birth canal, in spite of the presence of strong uterine contractions.[1] This phenomenon mostly occurs when the fetal head is not well-matched with the mother’s pelvic brim, known as cephalopelvic disproportion (CPD). Obstructed labor due to CPD remains a significant cause of short- and long-term disabilities in the newborn as well as an etiology of maternal morbidity and mortality.[2] CPD is generally more common in developing countries; besides, many pregnant women, particularly nulliparous ones want to know the probability of CPD in advance of labor to decide on the route of delivery.[3] Many complications can be prevented by identifying women at risk of difficult childbirth and referring them to well-equipped hospitals.[4]

The pelvis shape and size is a critical prerequisite for a NVD. Inappropriate pelvis brim can lead to adverse events such as premature rupture of membranes, inappropriate uterine contractions, abnormal fetal head position, and complicated labor.[2] Considering the socioeconomic effects of pelvis disorder, this condition is more frequent in developing countries.[3] Advanced pelvimetry methods such as pelvimetry with computer tomography, magnetic resonance, radiography, and ultrasound are expensive and are not widely available, especially in developing countries.[5,6] Also, these methods expose the fetus to ionizing radiation and increase the risk of childhood cancer.[7]

Since a long time ago, clinical pelvimetry has been introduced as a potential way to assess the maternal pelvic dimensions using internal and external calipers. Nevertheless, clinical pelvimetry can be performed during labor only, based on clinical and manual evaluation of the fetal station and the maternal pelvic dimensions.[8] Recent ideas questioned the utility of clinical pelvimetry as they believe that the process of giving birth is the most practical way to figure out the proportionality of fetal head with maternal pelvic; however, others favored it with the claim that this process might lead to detection of some points prognosticating the potential of CPD and prevent difficult labors.[9,10]

The development of imaging modalities has turned the attention toward more concise instruments; however, it was not without shortcomings. In addition to the costs of new modalities and their inaccessibility, radiography, and computed tomography assessments which are the most favored and readily available, predispose mothers and fetuses to X-radiations.[10,11] The other modality, magnetic resonance imaging (MRI) despite its superiority including not involving radiation and detecting some anatomical markers associated with CPD, has not revealed significantly better outcomes than those obtained using earlier pelvimetric techniques. The costs, difficulty of access, and the long-lasting process should be added for MRI not to be used practically and be limited to research.[7]

Ultrasonography is one of the most favored modalities in pregnancy prominently replacing ionizing ones. This means it is also available in numerous centers and is concise enough to detect most of the pathological conditions; however, it is generally dependent on the operator.[12] Despite a theoretical idea regarding sonopelvimetry, its utility has not been well-investigated. Accordingly, the major goal of this study is to evaluate the value of ultrasonography and clinical pelvimetry in evaluation of outcome and progress of vaginal delivery in nulliparous women.

MATERIALS AND METHODS

Study population

The current cross-sectional study has been conducted on 275 nulliparous women who refer to came for delivery to the obstetrics and gynecology wards of hospitals affiliated with Isfahan University of Medical Sciences from March 2021 to April 2022.

The study protocol was designed considering the tenets of the Helsinki Declaration, proposed to the Ethics Committee of Isfahan University of Medical Sciences, and approved via code number IR.MUI.MED.REC.1400.329. After the participants entered the study, they were asked to sign a written consent form, which assured them that their information would remain confidential.

Nulliparous singleton women of child-bearing ages with the gestational age of over 28 weeks and BMI at the beginning of pregnancy was under 30 kg/m² whose fetuses had a cephalic presentation based on the ultrasonographic studies were included. The exclusion criteria were delivery before the gestational age of 37 weeks, severe anxiety disorder, and fetal body weight of fewer than 2500 grams or more than 4500 grams (measured after delivery), and any indication for pregnancy termination via C/S (e.g. amniotic fluid contaminated with meconium, presentation of fetus changing to breech, decreased fetal heart rate, placental abruption, heavy bleeding, and low birth weight).

Based on the available samples, 210 primiparous women who came for delivery were included in the study, out of 275 cases that met the entry criteria.

The delivery was carried out via cesarean method due to certain conditions. Even though there were effective uterine contractions in the active stage of labor (dilation from 6–10 cm), the duration of the prolonged deceleration phase was more than three hours, or the secondary arrest of dilation lasted more than two hours, or the arrest of descent took more than one hour, or the duration of the second stage was more than two hours.[13]

Data collection

The participants who met the study criteria underwent clinical pelvimetry with an obstetrics and gynecology specialist to assess the pelvic inlet, mid-pelvic, and outlet regions. The subject’s demographic details and clinical pelvimetry parameters were recorded in the study questionnaire.

Clinical pelvimetry

A helpful clinical pelvimetry protocol has been developed, which involves examining the pelvic inlet, mid-pelvis, and pelvic outlet. During the clinical examination, reported average and critical-limit pelvic diameters can be used as a reference point to determine pelvic shape and assess the risk of CPD.[14]

During a vaginal examination, the examiner measures the diagonal conjugate or the anterior-posterior diameter of the pelvic inlet. This measurement is taken by determining the distance between the lower edge of the pubis symphysis and the sacral promontory, using the fingers of the examiner. Before the examination, the distance between the tip of the middle finger and the root of the thumb is measured and marked. A distance of less than 11.5 cm indicates pelvic inlet stenosis. If the examiner’s fingers reach the sacral promontory easily, the diagonal conjugate is considered short. If the sacral promontory is not touched or hardly touched, the anterior-posterior diameter of the pelvic inlet is appropriate.[15]

During a pelvic exam, a small mid-pelvic is identified when the iliac spines are completely prominent, the width of the sacrosciatic notch is less than the width of two fingers, the concavity and depression of the sacrum are completely smooth, and the distance between the ischial spines is less than 10 cm. To calculate the distance between the ischial spines, the index finger is placed on the ischial spine on one side of the hip and the middle finger is opened to the ischial spine on the opposite side. The sidewalls of the pelvis can be parallel, convergent, or divergent (starting from the pelvic brim down to the base of the ischial spines in the direction of the base of the ischial tuberosity). The relation between the index and middle finger of the base of the ischial spine and the thumb of the other hand placed on the ischial tuberosity was detected. If the thumb was medial, the sidewall was convergent, and if lateral, the pelvis was divergent [Figure 1].[14]

Figure 1.

Fellow chart of the studied samples

The transverse diameter of the pelvic outlet was determined by placing the fisted hand of the examiner whose size has been measured in advance in the distance between the ischial prominences. If the size was less than 9 cm or the pubic arch was less than two fingers, the pelvic outlet was considered narrow.[15]

Ultrasonography pelvimetry

Trans-abdominal ultrasound was used to measure the diagonal conjugate diameter. The measurement of the obstetric conjugate was performed using a 3.5 MHz trans-abdominal curvilinear probe. Longitudinal tomographic imaging was carried out at a site close to the pubic symphysis above the pubic bone on either the left or right side. The ultrasound obstetric conjugate was measured from the internal end of the superior periphery of the pubic bone to the sacral promontory, as described by Katanozaka et al.[16]

Statistical analysis

The obtained data was entered into the Statistical Package for Social Sciences (SPSS Inc. PASW statistics for Window Chicago) version 24. The categorical variables were presented in absolute numbers and percentages while quantitative variable was in mean ± standard deviation (SD). Chi-square or Fisher’s exact tests were applied to compare the categorical data. Quantitative variable was compared using an independent t-test. The receiver operating curve (ROC) was depicted to show the value of ultrasonography pelvimetry compared with clinical findings. A P value less than 0.05 is considered the level of significance.

RESULTS

In the current study, the eligibility of 275 patients for participation in the study was evaluated among whom 65 ones were excluded. A total of 8, 6, 5, 11, 4, 13, 2, and 16 participants withdrew from the study due to various reasons such as inappropriate cooperation, placenta decolman, bleeding, fetal abnormal presentation, meconium excretion, severe preeclampsia, fetal distress based on the fetal heart rate, over 4 kg fetal weight and preterm labor. Eventually, data from 210 nulliparous women were evaluated, including 186 (88.6%) who delivered their fetus through normal vaginal delivery (NVD) and 24 (11.4%) who had a C-section. Pelvimetry was used to assess the data. Figure 1 shows the chart of the included patients [Figure 2].

Figure 2.

Images related to external dimensions of the pelvis; pelvimetry

According to Table 1 of assessed clinical pelvimetry parameters, there was no significant difference in any of the parameters between those who delivered vaginally and those who delivered via C/S (P value > 0.05).

Table 1.

Frequency of diverse clinical pelvimetry parameters in women undergoing natural vaginal delivery versus cesarean section

Variables		Natural vaginal delivery		Cesarean section		P
		Frequency	Percentage	Frequency	Percentage
Sacral promontory	Touchable	52	28	7	29.2	0.901*
	Untouchable	134	72	17	70.8
Diagonal conjugate diameter	<11.5 cm	44	23.7	6	25	0.884*
	≥11.5 cm	142	76.3	18	75
Curvature of the Sacrum	Normal	165	88.7	21	87.5	0.869**
	Deep	9	4.8	1	4.2
	Smooth	12	6.5	2	8.3
Interspinous diameter	<10 cm	, 11	5.9	1	4.2	0.729*
	≥10 cm	175	94.1	23	95.8
Side walls	Convergent	11	5.9	1	4.2	0.729*
	Parallel (divergent)	175	94.1	23	95.8
Sacrosciatic notch	<two fingerbreadths	11	5.9	1	4.2	0.729*
	≥ two fingerbreadths	175	94.1	23	95.8
Sub-pubic arch	< two fingerbreadths	52	28	7	29.2	0.901*
	≥ two fingerbreadths	134	72	17	70.8
Prominence of coccyx	Mobile	182	97.8	24	100	0.999**
	Fixed	4	2.2	0	0
Intertuberous diameter	<9 cm	165	88.7	20	83.3	0.444*
	≥9 cm	21	11.3	4	16.7

*Chi-square. **Fisher’s exact test

The mean diagonal conjugate diameter as measured by ultrasonography was 119.29 ± 7.80 mm for C/Ss and 120.12 ± 8.72 mm for NVDs, with no statistically significant difference observed (P value = 0.659).

The comparison of ultrasonographic measured diagonal conjugate diameter between NVD and C/S women did not reveal any statistically significant differences in the frequencies of different diameters (P value > 0.05) [Table 1].

The data presented in Table 2 displays the clinical pelvimetry parameters that were assessed to determine whether performing a C/S rather than a vaginal delivery would prevent CPD. The analysis showed that none of the parameters could accurately predict the likelihood of CPD, and therefore, there was no statistically significant difference between C/S and vaginal delivery in terms of CPD prevention (P value > 0.05).

Table 2.

The value of clinical pelvimetry in the assessment of women undergoing cesarean section

Variables		Sensitivity	Specificity	Positive predictive value	Negative predictive value	Area under the curve	P
Pelvic inlet	Touchable sacral promontory	29.2	72	11.9	88.7	0.506	0.904
	Diagonal conjugate diameter <11.5 cm	25.0	76.3	12	88.7	0.507	0.888
Mid-pelvic	Smooth sacrum	95.8	4.8	11.5	90.0	0.503	0.880
	Interspinous diameter <10 cm	95.8	5.9	11.6	91.7	0.509	0.699
	Parallel pelvic side walls	95.8	5.9	11.6	91.7	0.509	0.699
	Sacrosciatic foramen < two fingerbreadths	95.8	5.9	11.6	91.7	0.509	0.699
Pelvic outlet	Sub-pubic arch < two fingerbreadths	29.2	72	11.9	88.7	0.506	0.904
	Fixed coccyx	100.0	2.2	11.7	100	0.511	0.044
	Intertuberous diameter <9 cm	16.7	88.7	16	89.2	0.527	0.507

A comparison was made between the diagnostic value of ultrasonographic measured diagonal conjugate diameter and clinical pelvimetry, and the results were displayed using a ROC curve [Figure 3]. However, despite the sensitivity, specificity, PPV, NPV, and AUC values of 70.8%, 47.3%, 14.8%, 92.6%, and 56.1%, respectively, at the cut-off point of 123 mm, the outcome was insignificant in terms of using this method as a substitute for clinical assessments for measuring diagonal conjugate diameter to determine the appropriate route for child delivery (P value = 0.263).

Figure 3.

ROC curve of ultrasonography diagonal conjugate diameter

DISCUSSION

Pelvimetry has been used for a long time to determine the route of child delivery. However, its reliability has been questioned due to certain limitations. Firstly, the only time to assess these proportions is during delivery, which can be too late for any intervention. Secondly, various investigations on this topic have revealed that despite the valuable results of pelvimetry, it is not precise enough to determine the route of delivery. On the other hand, with the development of imaging modalities, it has been assumed that they can provide better and more accurate information than clinical pelvimetry.[17]

The current study aimed to compare the clinical and ultrasonography pelvimetry outcomes of women who underwent NVD and those who had a cesarean section (C/S). However, our findings indicate that there were no significant differences between the two groups in terms of delivery method. Furthermore, neither clinical nor ultrasonographic pelvimetry measurements were able to accurately predict whether a woman would have a normal delivery or a C/S.

Studies have reported that there are significant differences in the measured items of pelvimetry between those who undergo NVD and those who undergo C/S. Alijahan et al.[18] examined pregnant women in two groups, NVD versus difficult delivery, and found that women with difficult deliveries had higher frequency of parameters including a smooth sacrum, ischia spines diameter of less than 10 cm, convergent pelvic wall, and pubic arch of less than 2 fingers and bilateral ischial prominence of less than 9 cm. They found the highest sensitivity for the pelvic inlet to predict the probability of a difficult delivery, but in general, and similar to the present study, their study showed that clinical pelvimetry is not appropriate for evaluating the possibility of NVD. Some studies have observed that touchable sacral promontory, narrow mid-pelvic, and pelvic outlet are the factors linked with difficult deliveries.[15,19] However, some studies, including ours, have found no association between pelvimetric parameters and delivery difficulty.[20,21]

It is possible that contradictory outcomes have arisen due to a comparison between C-section cases and cases of natural vaginal delivery (NVD), without considering the reason for the C-section or the varying durations of labor arrest in different studies. Furthermore, these factors are dependent on the number of C-sections performed.

The study evaluated the diagonal conjugate diameter using trans-abdominal ultrasonography as another parameter. The results showed that there were no significant differences between individuals undergoing NVD and cesarean section (C/S). Although this parameter had a high sensitivity rate of 70.8% at a cut-point of 123 mm, its predictive value was statistically insignificant (P value = 0.263). Perlman and colleagues conducted a study using ultrasonography to evaluate pelvic parameters. They were trying to determine the likelihood of unplanned operative delivery. The study found that two parameters, the pubic arch angle and the angle of progression, were crucial in predicting the success of NVD.[22] In another investigation, researchers compared trans-abdominal versus trans-vaginal ultrasonography to predict the possibility of NVD. They found that both methods had similar outcomes only for fetal head engagement. However, the other parameters did not show comparable results.[23] The other investigation by Di Pasquo et al.[24] determined that the ratio of fetal head circumference to obstetrical conjugate is a valuable determinant for NVD.

However, most of the studies in the literature have presented findings that differ from ours, which we believe is due to the small sample size of the C/S group compared to the NVD group.[22,23,24] Daghighi and colleagues performed a study in which they compared diagonal conjugate diameter between the women undergoing NVD versus C/S using ultrasonography modality and represented significantly wider diameters for those who delivered their child through the vaginal route. They continued that the cut-point of 119 mm was reasonable to determine whether or not a woman is anatomically appropriate for NVD.[25] Similarly, Adadevoh et al.[26] represented significantly narrower conjugates among those undergoing C/S. They found sensitivity and specificity of 80% and 78.5% for the cut-point of 120 mm to decide on C/S performance. In confirmation, another author presented that the diagonal conjugate diameter of less than 100 mm necessitates C/S, and those above 120 mm are the most appropriate cases for NVD; however, the diameters between these ranges are still questionable.[13] We conducted a study to determine the threshold for diagonal conjugate diameter that discriminates women who are suitable for NVD. Although previous studies in the literature[13,25,26] suggested a different threshold value, our findings indicate that the threshold is 123 mm. Our measurement has a relatively high sensitivity of 70.8%, but the calculated specificity was less than 50%. Additionally, we observed that the measurements we obtained were not statistically significant (P value = 0.263). Despite this, we believe that trans-vaginal ultrasonographic pelvimetry may be a better and more accurate method than abdominal ultrasonography, which is what we used in our study.

Strengths and limitations

Our results showed high reliability of ultrasonographic and intra-examiner pelvic measurements. Our radiologists were very experienced, and hence, the ultrasonography was accurate and reliable. Most women in our referral hospital had NVD, which may limit the results.

CONCLUSION

Based on the findings of this study, neither clinical pelvimetric parameters nor trans-abdominal ultrasonography could appropriately prognosticate delivery appropriateness through the vaginal route.

Ethics approval and consent to participate

The Isfahan University of Medical Sciences Ethics Committee (code: IR.MUI.MED.REC.1400.329) approved this study. Informed consent was obtained from all participants.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.