Establishing the Accuracy and Acceptability of Abdominal Ultrasound to Define the Foetal Head Position in the Second Stage of Labour

Accurate determination of the fetal head position in the passive second stage of labor is clinically important because malposition of the fetal head can lead to longer labors and higher rates of instrumental delivery and cesarean section. Studies have found that ultrasound assessment has been more accurate compared with digital vaginal examination. Performing an ultrasound assessment of the fetal head position during labor before instrumental delivery is an option. This study was undertaken to compare the diagnosis of the fetal head position by a novice and expert ultrasonographer, to compare the diagnosis of fetal head position by a clinician and an expert ultrasonographer, and to evaluate the acceptability of the ultrasound procedure to women in the second stage of labor and their caregivers. The study included nulliparous or multiparous women at term with singleton cephalic fetuses who were anticipating a vaginal delivery. Once the second stage of labor was reached, an ultrasound assessment was performed by a single novice sonographer, who had no experience in intrapartum ultrasound, followed by a single expert sonographer and a clinician. The operators did not reveal their findings to the others. For all ultrasound assessments, image-directed pulsed Doppler equipment with a multifrequency sector array transabdominal transducer and a 3.5-MHz sector ultrasound probe was used. The patients were placed in the supine or left lateral tilt position. The fetal head position was classified as OA for direct occipitoanterior; ROA and LOA for right and left OA, respectively; OP for direct occipitoposterior; ROP and LOP for right and left OP; and ROT and LOT for right and left occipitotransverse, respectively. The primary outcome was error in the diagnosis of the fetal head position, with diagnosis of the head position by the expert sonographer considered the criterion standard. The diagnosis was considered correct if it was within 45 degrees of the expert’s findings. The most clinically significant errors are those in which the misdiagnosis is between OA and OP (OA/OP errors) or a difference of 180 degrees between LOT and ROT. The patients and their caregivers completed questionnaires regarding the acceptability of the assessment. Sixty of the 107 women agreeing to participate had complete data sets with a total of 3 assessments performed, by the expert ultrasonographer, the novice ultrasonographer, and the clinician. All women had ruptured membranes and confirmed full cervical dilatation, and the fetal head was no more than 2 cm above the ischial spines. Fifty women (83%) had regional analgesia/anesthesia. It was technically possible for both the expert and novice ultrasonographer to define the fetal head position in all 60 patients. The proportions of the fetal head positions as determined by the expert sonographer were 2 (3%) OA, 27 (45%) LOA, 9 (15%) ROA, 3 (5%) LOT, 1 (2%) ROT, 11 (18%) LOP, and 7 (12%) ROP. The novice’s ultrasound findings agreed with those of the expert in 52 cases (87%) for the fetal head position and in 37 cases (62%) for the position of the fetal back. Although most of the errors made by the novice ultrasonographer were minor because of incorrect probe orientation leading to situs inversion (right-left errors), no OA-OP errors were made. The median time taken to perform the assessment was 60 seconds by the novice and 5 seconds by the expert. However, the novice became faster with an increasing number of cases (150 seconds for first 10 cases, 10 seconds for the last 10 cases). The clinician’s assessment agreed with the expert’s findings in 35 cases (58%) with 25 (42%) errors; 8 (13%) were OA/OP errors. Fifty-nine questionnaires were completed. No woman thought the ultrasound assessment was intrusive or bothersome, but 1 patient (2%) said it was uncomfortable. These results indicate that a novice sonographer can learn the ultrasound skills for accurate determination of the fetal head position in the passive second stage of labor quickly and easily. The standardized approach to ultrasound assessment, as used in this study, could be replicated by trainers and clinicians in other centers. Accurate diagnosis of the fetal head position is important when the second stage of labor is not progressing well, and an instrumental delivery is likely. Further research is required to establish whether ultrasound diagnosis of the fetal head position could be used to enhance the safety of instrumental delivery where morbidity often relates to failure to recognize fetal malposition.