Relative uteroplacental insufficiency of labor.

Relative uteroplacental insufficiency of labor (RUPI-L) is a clinical condition that refers to alterations in the fetal oxygen "demand-supply" equation caused by the onset of regular uterine activity. The term RUPI-L indicates a condition of "relative" uteroplacental insufficiency which is relative to a specific stressful circumstance, such as the onset of regular uterine activity. RUPI-L may be more prevalent in fetuses in which the ratio between the fetal oxygen supply and demand is already slightly reduced, such as in cases of subclinical placental insufficiency, post-term pregnancies, gestational diabetes, and other similar conditions. Prior to the onset of regular uterine activity, fetuses with a RUPI-L may present with normal features on the cardiotocography. However, with the onset of uterine contractions, these fetuses start to manifest abnormal fetal heart rate patterns which reflect the attempt to maintain adequate perfusion to essential central organs during episodes of transient reduction in oxygenation. If labor is allowed to continue without an appropriate intervention, progressively more frequent, and stronger uterine contractions may result in a rapid deterioration of the fetal oxygenation leading to hypoxia and acidosis. In this Commentary, we introduce the term relative uteroplacental insufficiency of labor and highlight the pathophysiology, as well as the common features observed in the fetal heart rate tracing and clinical implications.

Reproducibility analysis of two speckle tracking software for the antenatal semi-automated assessment of the fetal cardiac function.

Introduction Speckle tracking echocardiography (STE) is a non-Doppler modality allowing the semiautomated evaluation of the fetal cardiac function by tracking the speckles of the endocardial borders. Little evidence is available on the evaluation and comparison of different software for the functional assessment of the fetal heart by means of STE. The aim of this study is to evaluate the reproducibility and agreement of two different proprietary speckle tracking software for the prenatal semi-automated assessment of the fetal cardiac function. Methods Prospective study including non-anomalous fetuses referred for different indications at two tertiary academic units in Italy (University of Parma) and Spain (University of Barcelona). 2D clips of the four-chamber view of the fetal heart were acquired by two operators using high-end ultrasound machines with a frame rate higher than 60 Hz. The stored clips were pseudo-anonymized and shared between the collaborating Units. Functional echocardiographic analyses were independently performed using the two proprietary software (TomTec GmbH and FetalHQ®) by the same operators. Inter-software reproducibility of the endocardial global longitudinal strain (EndoGLS) and fractional area change (FAC) of the left (LV) and the right ventricles (RV) and ejection fraction (EF) of the LV were evaluated by the intraclass correlation coefficient (ICC). Results 48 fetuses were included at a median of 31+2 (21+6 - 40+3) gestational weeks. Moderate reproducibility was found for the functional parameters of the LV: EndoGLS (Pearson's correlation 0.456, p<0.01; ICC 0.446, 95%CI (0.189-0.647), p<0.01); EF (Pearson's correlation 0.435, p<0.01; ICC 0.419, 95%CI (0.156-0.627), p<0.01); FAC (Person's correlation 0.484, p<0.01; ICC 0.475, 95%CI (0.223-0.667), p<0.01). On the contrary, RV functional parameters showed poor reproducibility between the two software: EndoGLS (Pearson's correlation 0.383, p=0.01; ICC 0.377, 95%CI (0.107-0.596), p<0.01) and FAC (ICC 0.284, 95%CI (0.003-0.524), p=0.02). Conclusion Our results demonstrate a moderate reproducibility of the speckle tracking analysis of the LV using TomTec GmbH and FetalHQ®, with poor reproducibility for RV analysis.

A deep learning approach to identify the fetal head position using transperineal ultrasound during labor.

OBJECTIVES: To develop a deep learning (DL)-model using convolutional neural networks (CNN) to automatically identify the fetal head position at transperineal ultrasound in the second stage of labor. MATERIAL AND METHODS: Prospective, multicenter study including singleton, term, cephalic pregnancies in the second stage of labor. We assessed the fetal head position using transabdominal ultrasound and subsequently, obtained an image of the fetal head on the axial plane using transperineal ultrasound and labeled it according to the transabdominal ultrasound findings. The ultrasound images were randomly allocated into the three datasets containing a similar proportion of images of each subtype of fetal head position (occiput anterior, posterior, right and left transverse): the training dataset included 70 %, the validation dataset 15 %, and the testing dataset 15 % of the acquired images. The pre-trained ResNet18 model was employed as a foundational framework for feature extraction and classification. CNN1 was trained to differentiate between occiput anterior (OA) and non-OA positions, CNN2 classified fetal head malpositions into occiput posterior (OP) or occiput transverse (OT) position, and CNN3 classified the remaining images as right or left OT. The DL-model was constructed using three convolutional neural networks (CNN) working simultaneously for the classification of fetal head positions. The performance of the algorithm was evaluated in terms of accuracy, sensitivity, specificity, F1-score and Cohen's kappa. RESULTS: Between February 2018 and May 2023, 2154 transperineal images were included from eligible participants across 16 collaborating centers. The overall performance of the model for the classification of the fetal head position in the axial plane at transperineal ultrasound was excellent, with an of 94.5 % (95 % CI 92.0--97.0), a sensitivity of 95.6 % (95 % CI 96.8-100.0), a specificity of 91.2 % (95 % CI 87.3-95.1), a F1-score of 0.92 and a Cohen's kappa of 0.90. The best performance was achieved by the CNN1 - OA position vs fetal head malpositions - with an accuracy of 98.3 % (95 % CI 96.9-99.7), followed by CNN2 - OP vs OT positions - with an accuracy of 93.9 % (95 % CI 89.6-98.2), and finally, CNN3 - right vs left OT position - with an accuracy of 91.3 % (95 % CI 83.5-99.1). CONCLUSIONS: We have developed a DL-model capable of assessing fetal head position using transperineal ultrasound during the second stage of labor with an excellent overall accuracy. Future studies should validate our DL model using larger datasets and real-time patients before introducing it into routine clinical practice.

First-trimester ultrasound of the cerebral lateral ventricles in fetuses with open spina bifida: a retrospective cohort study.

BACKGROUND: Beyond 18 weeks of gestation, an increased size of the fetal lateral ventricles is reported in most fetuses with open spina bifida. In the first trimester of pregnancy, the definition of ventriculomegaly is based on the ratio of the size of the choroid plexus to the size of the ventricular space or the entire fetal head. However, contrary to what is observed from the midtrimester of pregnancy, in most fetuses with open spina bifida at 11 to 13 weeks of gestation, the amount of fluid in the ventricular system seems to be reduced rather than increased. OBJECTIVE: This study aimed to compare the biometry of the lateral ventricles at 11 0/7 to 13 6/7 weeks of gestation between normal fetuses and those with confirmed open spina bifida. STUDY DESIGN: This was a retrospective cohort study that included all cases of isolated open spina bifida detected at 11 0/7 to 13 6/7 weeks of gestation over a period of 5 years and a group of structurally normal fetuses attending at our center over a period of 1 year for the aneuploidy screening as controls. Transventricular axial views of the fetal brain obtained from cases and controls were extracted from the archive for post hoc measurement of cerebral ventricles. The choroid plexus-to-lateral ventricle length ratio, sum of the choroid plexus-to-lateral ventricle area ratio, choroid plexus area-to-fetal head area ratio, and mean choroid plexus length-to-occipitofrontal diameter ratio were calculated for both groups. The measurements obtained from the 2 groups were compared, and the association between each parameter and open spina bifida was investigated. RESULTS: A total of 10 fetuses with open spina bifida were compared with 358 controls. Compared with controls, fetuses with open spina bifida showed a significantly smaller size of the cerebral ventricle measurements, as expressed by larger values of choroid plexus-to-lateral ventricle area ratio (0.49 vs 0.72, respectively; P<.001), choroid plexus-to-lateral ventricle length ratio (0.70 vs 0.79, respectively; P<.001), choroid plexus area-to-fetal head area ratio (0.28 vs 0.33, respectively; P=.006), and choroid plexus length-to-occipitofrontal diameter ratio (0.52 vs 0.60, respectively; P<.001). The choroid plexus-to-lateral ventricle area ratio was found to be the most accurate predictor of open spina bifida, with an area under the curve of 0.88, a sensitivity of 90%, and a specificity of 82%. CONCLUSION: At 11 0/7 to 13 6/7 weeks of gestation, open spina bifida is consistently associated with a reduced amount of fluid in the lateral cerebral ventricles of the fetus, as expressed by a significantly increased choroid plexus-to-lateral ventricle length ratio, choroid plexus-to-lateral ventricle area ratio, choroid plexus area-to-fetal head area ratio, and choroid plexus length-to-occipitofrontal diameter ratio.

Assessment of the cerebroplacental ratio and uterine arteries in low-risk pregnancies in early labour for the prediction of obstetric and neonatal outcomes.

BACKGROUND: The evidence-based management of human labor includes the antepartum identification of patients at risk for intrapartum hypoxia. However, available evidence has shown that most of the hypoxic-related complications occur among pregnancies classified at low-risk for intrapartum hypoxia, thus suggesting that the current strategy to identify the pregnancies at risk for intrapartum fetal hypoxia has limited accuracy. OBJECTIVE: To evaluate the role of the combined assessment of the cerebroplacental ratio (CPR) and uterine arteries (UtA) Doppler in the prediction of obstetric intervention (OI) for suspected intrapartum fetal compromise (IFC) within a cohort of low-risk singleton term pregnancies in early labor. METHODS: Prospective multicentre observational study conducted across four tertiary Maternity Units between January 2016 and September 2019. Low-risk term pregnancies with spontaneous onset of labor were included. A two-step multivariable model was developed to assess the risk of OI for suspected IFC. The baseline model included antenatal and intrapartum characteristics, while the combined model included antenatal and intrapartum characteristics plus Doppler anomalies such as CPR MoM < 10th percentile and mean UtA Doppler PI MoM ≥ 95th percentile. Predictive performance was determined by receiver-operating characteristics curve analysis. RESULTS: 804 women were included. At logistic regression analysis, CPR MoM < 10th percentile (aOR 1.269, 95 % CI 1.188-1.356, P < 0.001), mean UtA PI MoM ≥ 95th percentile (aOR 1.012, 95 % CI 1.001-1.022, P = 0.04) were independently associated with OI for suspected IFC. At ROC curve analysis, the combined model including antenatal characteristics plus abnormal CPR and mean UtA PI yielded an AUC of 0.78, 95 %CI(0.71-0.85), p < 0.001, which was significantly higher than the baseline model (AUC 0.61, 95 %CI(0.54-0.69), p = 0.007) (p < 0.001). The combined model was associated with a 0.78 (95 % CI 0.67-0.89) sensitivity, 0.68 (95 % CI 0.65-0.72) specificity, 0.15 (95 % CI 0.11-0.19) PPV, and 0.98 (0.96-0.99) NPV, 2.48 (95 % CI 2.07-2.97) LR + and 0.32 (95 % CI 0.19-0.53) LR- for OI due to suspected IFC. CONCLUSIONS: A predictive model including antenatal and intrapartum characteristics combined with abnormal CPR and mean UtA PI has a good capacity to rule out and a moderate capacity to rule in OI due to IFC, albeit with poor predictive value.

Fetal face shape analysis from prenatal 3D ultrasound images.

3D ultrasound imaging of fetal faces has been predominantly confined to qualitative assessment. Many genetic conditions evade diagnosis and identification could assist with parental counselling, pregnancy management and neonatal care planning. We describe a methodology to build a shape model of the third trimester fetal face from 3D ultrasound and show how it can objectively describe morphological features and gestational-age related changes of normal fetal faces. 135 fetal face 3D ultrasound volumes (117 appropriately grown, 18 growth-restricted) of 24-34 weeks gestation were included. A 3D surface model of each face was obtained using a semi-automatic segmentation workflow. Size normalisation and rescaling was performed using a growth model giving the average size at every gestation. The model demonstrated a similar growth rate to standard head circumference reference charts. A landmark-free morphometry model was estimated to characterize shape differences using non-linear deformations of an idealized template face. Advancing gestation is associated with widening/fullness of the cheeks, contraction of the chin and deepening of the eyes. Fetal growth restriction is associated with a smaller average facial size but no morphological differences. This model may eventually be used as a reference to assist in the prenatal diagnosis of congenital anomalies with characteristic facial dysmorphisms.

Correlation between intrapartum CTG findings and interleukin-6 levels in the umbilical cord arterial blood: A prospective cohort study.

OBJECTIVE: to investigate the correlation between the intrapartum CardioTocoGraphic (CTG) findings "suggestive of fetal inflammation" ("SOFI") and the interleukin (IL)-6 level in the umbilical arterial blood. STUDY DESIGN: prospective cohort study conducted at a tertiary maternity unit and including 447 neonates born at term. METHODS: IL-6 levels were systematically measured at birth from a sample of blood taken from the umbilical artery. The intrapartum CTG traces were retrospectively reviewed by two experts who were blinded to the postnatal umbilical arterial IL-6 values as well as to the neonatal outcomes. The CTG traces were classified into "suggestive of fetal inflammation (SOFI)" and "no evidence of fetal inflammation (NEFI) according to the principles of physiologic interpretation the CTG traces. The CTG was classified as "SOFI" if there was a persistent fetal heart rate (FHR) increase > 10 % compared with the observed baseline FHR observed at the admission or at the onset of labor without any preceding repetitive decelerations. The occurrence of Composite Adverse Outcome (CAO) was defined as Neonatal Intensive Care Unit (NICU) or Special Care Baby Unit (SCBU) admission due to one or more of the following: metabolic acidaemia, Apgar score at 5 min ≤ 7, need of neonatal resuscitation, respiratory distress, tachypnoea/polypnea, jaundice requiring phototherapy, hypotension, body temperature instability, poor perinatal adaptation, suspected or confirmed early neonatal sepsis. MAIN OUTCOME MEASURES: To compare the umbilical IL-6 values between the cases with intrapartum CTG traces classified as "SOFI" and those classified as "NEFI"; to assess the correlation of umbilical IL-6 values with the neonatal outcome. RESULTS: 43 (9.6 %) CTG traces were categorized as "SOFI"; IL-6 levels were significantly higher in this group compared with the "NEFI" group (82.0[43.4-325.0] pg/ml vs. 14.5[6.8-32.6] pg/mL; p <.001). The mean FHR baseline assessed 1 h before delivery and the total labor length showed an independent and direct association with the IL-6 levels in the umbilical arterial blood (p <.001 and p = 0.005, respectively). CAO occurred in 33(7.4 %) cases; IL-6 yielded a good prediction of the occurrence of the CAO with an AUC of 0.72 (95 % CI 0.61-0.81). CONCLUSION: Intrapartum CTG findings classified as "SOFI" are associated with higher levels of IL-6 in the umbilical arterial blood.

Real-time ultrasound to assist during a vaginal breech delivery.

We report a novel application of intrapartum sonography, herein used to assist the internal podalic version and the vaginal delivery of a transverse-lying second twin. Following the vaginal delivery of the first cephalic twin, the internal podalic version was performed under continuous ultrasound vision, leading to the uncomplicated breech delivery of a healthy neonate.

The "cortical invagination sign": a midtrimester sonographic marker of unilateral cortical focal dysgyria in fetuses with complete agenesis of the corpus callosum.

BACKGROUND: Agenesis of the corpus callosum is associated with several malformations of cortical development. Recently, features of focal cortical dysgyria have been described in fetuses with agenesis of the corpus callosum. OBJECTIVE: This study aimed to describe the "cortical invagination sign," a specific sonographic feature of focal cortical dysgyria, which is consistently seen at midtrimester axial brain ultrasound in fetuses with complete agenesis of the corpus callosum. STUDY DESIGN: This was a retrospective analysis of prospectively collected data from 2018 to 2021, including patients referred to 5 fetal medicine centers in the second trimester of pregnancy (19 0/7 to 22 0/7 weeks of gestation) with suspected complete agenesis of the corpus callosum. All cases with the diagnosis of complete agenesis of the corpus callosum were submitted to an axial sonographic assessment of the fetal brain on the transventricular plane. In this scanning section, the mesial profile of both cerebral hemispheres at the level of the frontal-parietal cortex was investigated. In this area, the operator looked for an abnormal invagination of the cortical surface along the widened interhemispheric fissure, which was referred to as the "cortical invagination sign." All fetuses were submitted to dedicated antenatal magnetic resonance imaging to reassess the ultrasound findings. Cases with additional brain anomalies, which did not involve the cortex, were excluded. The final diagnosis was confirmed at postnatal brain magnetic resonance imaging or postmortem examination, for cases undergoing termination of pregnancy. The primary outcome of this study was to evaluate the presence and laterality of the "cortical invagination sign" in fetuses with complete agenesis of the corpus callosum at antenatal ultrasound and magnetic resonance imaging. RESULTS: During the study period, 64 cases of complete agenesis of the corpus callosum were included; of those cases, 50 (78.1%) resulted in termination of pregnancy, and 14 (21.9%) resulted in a live birth. The "cortical invagination sign" was detected at ultrasound in 13 of 64 cases (20.3%) and at targeted brain magnetic resonance imaging in 2 additional cases (23.4%), all of which were electively terminated. Moreover, the "cortical invagination sign" was found to be exclusively unilateral and on the left cerebral hemisphere in all the cases. There was a predominant number, although nonsignificant, of male fetuses (80.0% of cases; P=.06) in the group of complete agenesis of the corpus callosum with the "cortical invagination sign." CONCLUSION: The "cortical invagination sign" is a specific marker of focal cortical dysgyria, which seems to characterize at midtrimester of pregnancy in a large group of fetuses with complete agenesis of the corpus callosum. The etiology, pathophysiology, and prognostic significance of this finding remain to be elucidated.

Prenatal and Neonatal Bone Health: Updated Review on Early Identification of Newborns at High Risk for Osteopenia.

Bone health starts with maternal health and nutrition, which influences bone mass and density already in utero. The mechanisms underlying the effect of the intrauterine environment on bone health are partly unknown but certainly include the 'foetal programming' of oxidative stress and endocrine systems, which influence later skeletal growth and development. With this narrative review, we describe the current evidence for identifying patients with risk factors for developing osteopenia, today's management of these populations, and screening and prevention programs based on gestational age, weight, and morbidity. Challenges for bone health prevention include the need for new technologies that are specific and applicable to pregnant women, the foetus, and, later, the newborn. Radiofrequency ultrasound spectrometry (REMS) has proven to be a useful tool in the assessment of bone mineral density (BMD) in pregnant women. Few studies have reported that transmission ultrasound can also be used to assess BMD in newborns. The advantages of this technology in the foetus and newborn are the absence of ionising radiation, ease of use, and, above all, the possibility of performing longitudinal studies from intrauterine to extrauterine life. The use of these technologies already in the intrauterine period could help prevent associated diseases, such as osteoporosis and osteopenia, which are characterised by a reduction in bone mass and degeneration of bone structure and lead to an increased risk of fractures in adulthood with considerable social repercussions for the related direct and indirect costs.

Effect of the "shoulder-up" bundle on the incidence of spontaneous perineal injury after vaginal delivery: comparison of 2 historic cohorts after propensity score matching.

BACKGROUND: Perineal injury following vaginal delivery represents a major cause of long-term maternal morbidity, and its prevention is among the priorities of modern obstetrical practice. OBJECTIVE: This study aimed to investigate whether the systematic implementation of a bundle of maneuvers to prevent perineal injury (ie, the "shoulder-up" bundle) may reduce the rate of spontaneous perineal tears in women delivering at a single tertiary maternity unit. STUDY DESIGN: This was a single-center retrospective intervention study including all vaginal deliveries between April 1, 2020 and March 31, 2022. On March 1, 2021, a bundle focused on perineal injury prevention in vaginal deliveries was implemented and introduced as a standard of care. The "shoulder-up" bundle includes the addition of a hands-on technique for the delivery of the posterior shoulder, which is slowly lifted up under the direct visualization of the perineal body, immediately after the disengagement of the anterior shoulder. The labor ward staff underwent dedicated training to acquire expertise on the "shoulder-up" bundle. Little changes in terms of medical and midwifery staffing were recorded during the study period. The incidence of spontaneous second-degree or higher perineal tears was compared between the patients who gave birth before the clinical implementation of the bundle (standard-care group) and those who were delivered following the implementation of the bundle (shoulder-up group). A 1:1 propensity score matching of the 2 groups was done for the variables that proved to be independently associated with the perineal outcome. RESULTS: From April 1, 2020 to March 31, 2022, 3671 patients had a vaginal birth at our tertiary care unit (1786 in the standard-care group and 1885 in the "shoulder-up" group) and were enrolled in the study population. Of these, 1191 (32.4%) had a spontaneous second-degree or higher perineal tear. At univariate analysis, nulliparity (59.6% vs 39.1%; P<.001), higher gestational age at delivery (39.8±1.28 vs 39.4±1.97 weeks; P<.001), epidural analgesia (40.6% vs 31.2%; P<.001), vacuum-assisted delivery (9.6% vs 4.0%; P<.001), and birthweight >4 kg (11.0% vs 6.3%; P<.001) were independently associated with the perineal outcome. Following propensity score matching for the above cited factors, the 1703 patients of each group were compared. A significant increase in the rate of intact perineum (71.0% vs 64.1%; P=.014) and a reduction in the incidence of second- (27.2% vs 32.9%; P=.006) and third to fourth-degree perineal tears (1.3% vs 3.0%; P<.001) was demonstrated in the "shoulder-up" group. Among the subgroup of patients undergoing vacuum-assisted delivery, a borderline significant reduction in the rate of obstetrical anal sphincter injury (10.4% vs 2.9%; P=.052) was also observed. CONCLUSION: Our study showed that the clinical implementation of the "shoulder-up" bundle at vaginal delivery is associated with a significant reduction in the incidence of spontaneous second-degree or higher perineal tears.

An update on maternal cardiac hemodynamics in fetal growth restriction and pre-eclampsia.

Pre-eclampsia and fetal growth restriction (FGR) have been long related to primary placental dysfunction, caused by abnormal trophoblast invasion. Nevertheless, emerging evidence has led to a new hypothesis for the origin of pre-eclampsia and FGR. Suboptimal maternal cardiovascular adaptation has been shown to result in uteroplacental hypoperfusion, ultimately leading to placental hypoxic damage with secondary dysfunction. In this review, we summarize current evidence on maternal cardiac hemodynamics in FGR and pre-eclampsia. We also discuss the different approaches for antihypertensive treatment according to the hemodynamic phenotype observed in pre-eclampsia and FGR.

Head-to-perineum distance measured transperineally as a predictor of failed midcavity vacuum-assisted delivery.

BACKGROUND: During the second stage of labor, in case of a need for a fetal extraction at midcavity, the choice of attempting the procedure between operative vaginal delivery and cesarean delivery is difficult. Moreover, guidelines on this subject are not clear. OBJECTIVE: This study aimed to identify antenatal and intrapartum parameters associated with a failed midcavity vacuum-assisted delivery and its association with maternal and neonatal adverse outcomes. STUDY DESIGN: This was a single-center, retrospective, cohort study conducted at a tertiary maternity hospital in France from January 2010 to December 2020. Women with singleton pregnancies under epidural analgesia with nonanomalous cephalic presenting fetuses and gestational ages at ≥37 weeks of gestation, who were submitted to midcavity vacuum-assisted delivery, were included. Following the American College of Obstetricians and Gynecologists definition, midcavity was defined as the presenting part of the fetus (ie, the fetal head) found at stations 0 and +1. For research purposes, all patients were submitted to transperineal ultrasound to evaluate the head-to-perineum distance, however, this measurement did not affect the decision to perform a midcavity vacuum-assisted delivery. The primary outcome of the study was failed midcavity vacuum-assisted delivery leading to cesarean delivery or the use of a different instrument to achieve vaginal delivery. RESULTS: Overall, 951 cases of midcavity vacuum-assisted delivery were included in this study. Failed midcavity vacuum-assisted delivery occurred in 242 patients (25.4%). Factors independently associated with failed midcavity vacuum-assisted delivery included maternal height (adjusted odds ratio, 0.96; 95% confidence interval, 0.94-0.99; P=.002), duration of the active phase of the first stage of labor (adjusted odds ratio, 1.11; 95% confidence interval, 1.05-1.17; P<.001), nonocciput anterior fetal head position (adjusted odds ratio, 1.47; 95% confidence interval, 1.06-2.04; P=.02), z score of the head-to-perineum distance (adjusted odds ratio, 1.23; 95% confidence interval, 1.05-1.43; P=.01), and birthweight of >4000 g (adjusted odds ratio, 2.04; 95% confidence interval, 1.28-3.26; P=.003). Women submitted to a failed midcavity vacuum-assisted delivery were more likely to have a major postpartum hemorrhage (7.1% vs 2.0%; P<.001), whereas neonates were more likely to have an umbilical artery pH of <7.1 (30.5% vs 19.8%; P=.001), be admitted to the neonatal intensive care unit (9.6% vs 4.7%; P=.005), and have a severe caput succedaneum (14.9% vs 0.7%; P<.001). Subgroup analysis on all patients with a fetal head station of 0 found that the head-to-perineum distance was the only independent variable associated with failed midcavity vacuum-assisted delivery (adjusted odds ratio, 1.66; 95% confidence interval, 1.29-2.12; P<.001). The area under the receiving operating characteristic curve of the head-to-perineum distance in this subgroup population was 0.67 (95% confidence interval, 0.60-0.73; P<.001), and the optimal cutoff point of the head-to-perineum distance measurement discriminating between failed and successful midcavity vacuum-assisted deliveries was 55 mm. It was associated with a 0.90 (95% confidence interval, 0.83-0.95) sensitivity, 0.19 (95% confidence interval, 0.14-0.25) specificity, 0.36 (95% confidence interval, 0.30-0.42) positive predictive value, and 0.80 (95% confidence interval, 0.66-0.90) negative predictive value. CONCLUSION: Study data showed that a high fetal head station, measured using the head-to-perineum distance, and a nonocciput anterior position of the fetal head are independently associated with failed midcavity vacuum-assisted delivery. The result supported the systematic assessment of the sonographic head station and position before performing a midcavity vacuum-assisted delivery.