The digital determination of the fetal head position using an obstetric exploration that requires training is greatly influenced by the laboring woman’s degree of cervical dilation and has added difficulties with the presence of caput succedaneum or asynclitism. Some studies have shown that the digital determination of fetal head position with respect to the maternal pelvis during labor is not exact [6, 7]. Likewise, Akmal et al. [8] conducted a study of 496 abdominal ultrasounds after digital exploration and found that fetal head position could not be determined via vaginal touch in 33% of the cases, especially in cases with occipitoposterior positions [9]. Souka et al. [10] could not determine fetal head position in 61% of subjects during the first stage of labor and in 31% during the second stage. In a study of 44 pregnant women in the intrapartum setting, Kreise et al. [11] found erroneous interpretations of fetal head position in 30% of cases after digital exploration. Dupuis et al. [12] found a 70% concordance of both methods in determining fetal head position, with more difficulties observed in cases with caput succedaneum and posterior positions.

Chou et al. [13] found greater precision for determining occipitoposterior positions with transabdominal ultrasound than with vaginal touch (92% vs. 72%, respectively). Zahalka et al. [14] compared the use of vaginal touch, transabdominal ultrasound, and transvaginal ultrasound to determine fetal head position and found that transvaginal ultrasound was the most exact method. In our center, which had an average of 7,900 births in the last 10 years and an average C-section rate lower than 12%, we believe that there is no substitute for adequate clinical management; however, the majority of delivering obstetricians find that transabdominal or translabial ultrasound is useful for determining fetal head position, primarily at the point at which an instrumental delivery is indicated [15]. In other centers with perhaps less clinical experience, ultrasound could be useful for decreasing the number of C-sections performed defensively by obstetricians who wish to avoid the possibility of a complicated ­delivery [16].

In a recently published article, we evaluated the usefulness of transabdominal ultrasound to determine fetal head position during the first and second stages of labor in 86 consecutive patients [1]. With the patient in the decubitus supine position or the dorsal lithotomy position after bladder-emptying, we placed the abdominal probe transversally in the suprapubic area. The fetal head position was defined by the identification of the orbits (occipitoposterior), midline echo (occipitotransverse), and cerebellum or column (occipitoanterior) [17] (Fig. 2.3a, b). Using transvaginal exploration followed by transabdominal ultrasound, we did not find significant differences between these methods’ ability to determine the fetal head position. Clinically, it was possible to determine fetal head position in 93% of the patients in the first stage of labor and in 96% of the patients in the second stage of labor, and there was a concordance with the ultrasound results in 98% of the cases. A body mass index in the top 15% of women was the only significant factor that made transabdominal ultrasound exploration difficult, while the presence of caput succedaneum was important for determining fetal head position [1]. Instrumental delivery with forceps or a vacuum requires awareness of the fetal head position because the incorrect application of these instruments can lead to adverse results. Wong et al. [18] randomized 50 patients with a prolonged second stage of labor prior to vacuum extraction to digital pelvic exploration only or transabdominal ultrasound exploration in conjunction with digital exploration. The authors showed that including ultrasound allowed a more precise application of the vacuum extractor. In our studies, we determined the exact clinical and ultrasound fetal head position prior to the ­application of forceps in 13 cases. In our center, which has a C-section rate of approximately 12% and a forceps delivery rate of 14%, it is imperative to determine the fetal head position for better labor management. In contrast, Akmal et al. [19] studied 64 labors prior to instrumental delivery and found that digital exploration failed to determine the fetal head position in 26% of the cases. The existence of a higher C-section rate or the use of vacuum extraction as the instrumental technique of choice may be responsible for the inaccuracy of fetal head position determination via transvaginal exploration. The differences in the published data demonstrate the need for a prospective study to more precisely specify the usefulness of ultrasound to determine the fetal head position prior to an instrumental delivery.

To a lesser extent, studies have also described the determination of fetal head position using 3D transperineal ultrasound [20]. In our center, we obtained 20 captures of sutures and fontanels using translabial ultrasound with a transabdominal probe. Such volumetric captures allow us to identify the sutures and fontanels of the fetal head, which is useful prior to an instrumental delivery or when deciding whether to allow a vaginal delivery attempt or perform C-section (Fig. 2.4a, b).

The objective information about the fetal head position that 2D or 3D ultrasound provides prior to an instrumental delivery appears to be among the most useful data for decreasing the number of C-sections or adverse results after the inadequate performance of instrumental deliveries.

If the fetal head position is anterior, posterior, or transverse, ultrasound is clearly warranted to determine the exact fetal position before delivery; however, using ultrasound during delivery can also provide objective data for diagnosing inadequate progression of labor [8, 21]. Currently, the number of C-sections is increasing in an unjustified manner, often due to the practice of defensive medicine. We commented previously on the impreciseness of digital touch for the evaluation of the fetal head position relative to the maternal pelvis [22]; the combination of ultrasound exploration with clinical exploration could be useful for decreasing the number of C-sections.

The inaccuracy of clinical examination during labor has also been demonstrated regarding the descent of the head across the different planes of the maternal pelvis. Dupuis et al. [23] investigated the reliability of transvaginal assessment of fetal head station using a newly designed birth simulator. A fetal head mannequin was placed in one of the 11 American College of Obstetricians and Gynecologists (ACOG) stations in a birth simulator equipped with a real-time miniaturized sensor. The operators (32 residents and 25 obstetricians) then determined the head position clinically. The ACOG position was incorrectly determined in 50–88% of cases for residents and in 36–80% of cases for obstetricians, depending on the position. When the stations were examined in groups (high, midpelvis, low, and outlet), the mean group error was 30% (95% CI: 25–35%) for residents and 34% (95% CI: 27–41%) for obstetricians. Alarmingly, the group errors show that the misdiagnosis of a station as midpelvic rather than high-pelvic accounted for 88% and 67% of the errors made by residents and obstetricians, respectively. This misdiagnosis can have serious implications for the management of patients in labor.

To determine the progression of labor using either 2D or 3D sonography, the exploration must be performed translabially. The patient must be placed in a semicurved position with flexed legs, and amniotomy is recommended [24]. The ultrasound transducer is placed in the medial sagittal plane, between the labia majora and precisely below the symphysis pubis. Several studies have used ultrasound to provide an objective measure of head progression in labor: