Background
Occiput posterior position is the most frequent cephalic malposition, and its persistence at delivery is associated with a higher risk of maternal and perinatal morbidity. Diagnosis and management of occiput posterior position remain a clinical challenge. This is partly caused by our inability to predict fetuses who will spontaneously rotate into occiput anterior from those who will have persistent occiput posterior position. The angle of progression, measured with transperineal ultrasound, represents a reliable tool for the evaluation of fetal head station during labor. The relationship between the persistence of occiput posterior position and fetal head station in the second stage of labor has not been previously assessed.
Objective
This study aimed to evaluate the role of fetal head station, as measured by the angle of progression, in the prediction of persistent occiput posterior position and the mode of delivery in the second stage of labor.
Study Design
We recruited a nonconsecutive series of women with posterior occiput position diagnosed by transabdominal ultrasound in the second stage of labor. For each woman, a transperineal ultrasound was performed to measure the angle of progression at rest. We compared the angle of progression between women who delivered fetuses in occiput anterior position and those with persistent occiput posterior position at delivery. Receiver operating characteristics curves were performed to evaluate the accuracy of the angle of progression in the prediction of persistent occiput posterior position. Finally, we performed a multivariate logistic regression to determine independent predictors of persistent occiput posterior position.
Results
Overall, 63 women were included in the analysis. Among these, 39 women (62%) delivered in occiput anterior position, whereas 24 (38%) delivered in occiput posterior position (persistent occiput posterior position). The angle of progression was significantly narrower in the persistent occiput posterior position group than in women who delivered fetuses in occiput anterior position (118.3°±12.2° vs 127.5°±10.5°; P =.003). The area under the receiver operating characteristics curve was 0.731 (95% confidence interval, 0.594–0.869) with an estimated best cutoff range of 121.5° (sensitivity of 72% and specificity of 67%). On logistic regression analysis, the angle of progression was found to be independently associated with persistence of occiput posterior position (odds ratio, 0.942; 95% confidence interval, 0.889–0.998; P =.04). Finally, women who underwent cesarean delivery had significantly narrower angle of progression than women who had a vaginal delivery (113.5°±8.1 vs 128.0°±10.7; P <.001). The area under the receiver operating characteristics curve for the prediction of cesarean delivery was 0.866 (95% confidence interval, 0.761–0.972). At multivariable logistic regression analysis including the angle of progression, parity, and gestational age at delivery, the angle of progression was found to be the only independent predictor associated with cesarean delivery (odds ratio, 0.849; 95% confidence interval, 0.775–0.0930; P <.001).
Conclusion
In fetuses with occiput posterior at the beginning of the second stage of labor, narrower values of the angle of progression are associated with higher rates of persistent occiput posterior position at delivery and a higher risk of cesarean delivery.
Introduction
Occiput posterior (OP) position is the most frequent cephalic malposition. To date, OP position remains a clinical challenge from both a diagnosis and management points of view. Although OP position can be found in up to 25% early in labor, most of these will rotate into the more favorable occiput anterior (OA) position, and few will remain in OP position at delivery (persistent OP position). Persistent OP position is associated with longer labor durations and with a higher risk of maternal and perinatal morbidity. Traditionally, fetal head position is determined by digital vaginal examination. However, many studies have demonstrated that digital examination is not accurate and is poorly reproducible for the aim of fetal occiput position depiction. , The use of ultrasound in the labor ward has been suggested as a useful and reliable complementary tool to clinical examination. In particular, many studies have demonstrated that transabdominal ultrasound is superior to digital examination in the diagnosis of fetal occiput position. , , Nonetheless, the management of OP position remains a challenge. In the second stage of labor, management options include expectant management, which is the gold standard in many clinical realities, whereas the use of manual rotation is often advocated by some. , In the time being, there are insufficient data on which is the most appropriate management plan for OP position. , , The lack of a universal consensus on the management of OP position is at least partly caused by our inability to predict fetuses who will spontaneously rotate into OA from those who will have persistent OP position.
Why was this study conducted?
The angle of progression, measured by transperineal ultrasound, is a reliable tool for assessing the fetal head station. Its role in the prediction of rotation and the mode of delivery in occiput posterior position has been scarcely studied.
Key findings
A high fetal head station as measured by the angle of progression in fetuses in occiput posterior position during the second stage of labor was associated with higher rates of persistent occiput posterior position and cesarean delivery.
What does this add to what is known?
The angle of progression can be used in the prediction of persistent occiput posterior position and mode of the delivery.
Transperineal ultrasound (TPU) has been suggested as an objective, accurate, and reliable tool for the evaluation of fetal head descent. , , The angle of progression (AoP) represents one of the most studied indices of the fetal head station. , , Most studies on AoP have included mostly or exclusively fetuses in OA position. , , The role of fetal head descent as measured by TPU in the prediction of the persistence of OP position in the second stage of labor has not been previously assessed.
This study aimed to assess the role of fetal head descent, as measured by AoP, in the prediction of persistent OP position and the mode of delivery in the second stage of labor.
Materials and Methods
This was a prospective 2-center observational study conducted in 2 tertiary-level university hospitals (Sant’Orsola-Malpighi University Hospital, University of Bologna, Bologna, Italy, and Kasr Al-Ainy University Hospital, Cairo University, Cairo, Egypt) between June 2018 and December 2019. We recruited a nonconsecutive series of women with singleton pregnancy and fetuses in cephalic presentation at term of gestation (37–41 weeks). Women were recruited in the labor ward at the beginning of the second stage of labor, defined as the moment at which women were diagnosed to have reached full cervical dilatation at digital examination. We excluded women with previous uterine surgery, suspected fetal asphyxia, major fetal malformations, and OA and transverse positions at transabdominal scan performed at the beginning of the second stage of labor. All women were recruited when one of the investigators with more than 2 years of experience in TPU was present in the labor ward. While present in the labor ward exclusively for the aim of the study, the investigators invited all women who fulfilled the enrolment criteria to participate in the study. Investigators who performed the ultrasound scan were not blinded regarding the cervical dilatation because full cervical dilatation was a prerequisite for enrolment. However, they were blinded to all other clinical data such as fetal head station and clinical occiput position, caput, and molding. On the other side, clinicians and midwives involved in the management of labor were blinded to the ultrasound findings. Immediately after vaginal examination with confirmation of full cervical dilatation, one of the investigators performed a transabdominal ultrasound. In the case of OP position confirmed with sonography, a TPU scan was subsequently performed. All scans were performed using a Voluson P8 ultrasound machine (GE Medical Systems, Zipf, Austria) in Bologna and Samsung SONOACE R3 (Samsung Medison Co, Seoul, South Korea) and Toshiba Nemio XG (SSA-580A; Toshiba medical system Corp, Tochigi, Japan) in Cairo. Ultrasound machines were equipped with a convex transducer. Manual rotation of the fetal head and rotational forceps are never performed in any of the 2 centers.
Transabdominal ultrasound for the determination of fetal occiput position
Transabdominal scan was performed as previously described. , The ultrasound probe was placed horizontally on the maternal abdomen, and a transverse view of the fetal trunk was obtained. Subsequently, the probe was moved caudally on the maternal abdomen to reach the suprapubic region. After visualizing the fetal head, the principal landmarks of each fetal head position were depicted. These included the midline of the fetal brain, fetal thalami, and cerebellum for the occiput transverse and OA positions and the fetal orbits for OP position.
Transperineal ultrasound scan
The transducer was positioned transperineally on the midsagittal plane, visualizing the pubic symphysis and the fetal skull as previously described. The AoP was then measured at rest, in the absence of maternal pushing or uterine contractions. AoP is defined as the angle between the longitudinal axis of the pubic symphysis and a line that joins the lowest border of the pubis symphysis and the lowest part of the fetal skull.
After delivery, investigators consulted women’s medical records and collected the following data: maternal age, body mass index, parity, gestational age, mode of delivery, fetal occiput position at delivery, and birthweight. We compared AoP values, maternal characteristics, and labor outcomes between women with a fetus in persistent OP position and those with OA position at delivery. In addition, we compared AoP values and patient characteristics between women who delivered by cesarean delivery and those who delivered vaginally ( Figures 1 and 2 ).
Statistics
Mean, standard deviation, range, and frequencies were used as descriptive statistics. Differences between women with a fetus in persistent OP position and those with anterior occiput position at delivery and between the cesarean and vaginal delivery groups were assessed by unpaired 2-tailed Student t test for continuous variables and Fisher exact test for categorical variables. Receiver operating characteristics (ROC) curves were constructed to estimate the accuracy of AoP in predicting persistent OP position and cesarean delivery. The area under the ROC curve (AUC) was computed together with the standard error and the 95% confidence interval [CI]. The best cutoff values were calculated by means of a maximum likelihood ratio method. Finally, univariable and stepwise forward multivariable logistic regression analyses were performed by taking into account AoP, parity, and gestational age to identify independent predictors of persistent OP position and cesarean delivery. Data were analyzed using 25.0 SPSS version (SPSS Inc, Chicago, IL), and 2-tailed P <.05 was considered statistically significant. This was a pilot study, so no sample size calculation was needed.
Ethics
The local research ethics committees of the 2 participating hospitals approved the study protocol before the start of the study (reference number 39/2016/U/Oss for Bologna University Hospital and O18010 for Cairo University Hospital). All study participants provided an written informed consent before enrolment.
Results
We enrolled 420 women at the beginning of the second stage of labor. Among these, 357 women were excluded after the transabdominal ultrasound showed OA (n=315) or occiput transverse (n=42) position. Overall, 63 women were in OP position at the beginning of the second stage of labor and were recruited for the purpose of the study. A flowchart illustrating the study population is shown in Figure 3 .
Persistent occiput posterior position
Characteristics of the study population and characteristics subdivided between fetuses in persistent OP position and fetuses in OA position at delivery are presented in Table 1 . In our population, 24 women (38%) delivered in persistent OP position, whereas 39 women (62%) delivered in OA position ( Figure 3 ). Women in the persistent OP position group presented a higher prevalence of nulliparity and greater gestational age than women in the OA group. AoP was significantly narrower in women in the persistent OP position group than the OA position group at delivery (118.3°±12.2° vs 127.5°±10.5°; P =.003) ( Table 1 ). The higher the fetal head at the beginning of the second stage of labor (less engagement) as measured by the AoP, the higher the risk of persistent OP position. Moreover, women in the persistent OP position group had higher rates of both instrumental and cesarean deliveries. No difference in terms of birthweight and access to the neonatal intensive care unit was demonstrated between the 2 groups. The AUC for AoP in the prediction of persistent OP position was 0.731 (95% CI, 0.594–0.869) with an estimated best cutoff range of 121.5° (sensitivity of 72% and specificity of 67%) ( Figure 4 ). At multivariable logistic regression analysis including AoP, parity, and gestational age at delivery, AoP was found to be the only independent predictor associated with persistent OP position (odds ratio [OR], 0.942; 95% CI, 0889–0.998; P =.04).
| Characteristic | Total(N=63) | Persistent occiput posterior position (n=24) | Occiput anterior position at delivery (n=39) | P value a |
|---|---|---|---|---|
| Age, y | 28.9±6.0 | 28.7±6.1 | 29.1±6.0 | .79 |
| BMI, kg/m 2 | 29.2±3.8 | 28.6±2.8 | 29.7±4.2 | .24 |
| Parity | 1.4±1.6 | 0.7±1.2 | 1.8±1.7 | .008 |
| Nulliparity | 29 (46.0) | 15 (62.5) | 14 (35.9) | .04 |
| Gestational age, wk | 38.9±1.2 | 39.4±1.2 | 38.6±1.18 | .01 |
| AoP, ° | 124.0±11.9 | 118.3±12.2 | 127.5±10.5 | .003 |
| Mode of delivery | ||||
| Spontaneous vaginal delivery | 41 (65.1) | 6 (25.0) | 35 (89.7) | <.001 |
| Instrumental delivery | 5 (7.9) | 5 (20.8) | 0 (0) | <.001 |
| Cesarean delivery | 17 (27.0) | 13 (54.2) | 4 (10.3) | <.001 |
| Birthweight, g | 3329±416 | 3318±423 | 3335±417 | .88 |
| NICU | 8 (12.7) | 3 (12.5) | 5 (12.8) | .97 |
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