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Ultrasound Is an Important Diagnostic Tool in Active Labor

Eggebø, Torbjørn Moe1,2,3,∗

Editor(s): Pan, Yang

Author Information
doi: 10.1097/FM9.0000000000000001
  • Open

Cesarean section rates are rising worldwide, and in many countries the rate is much higher than medical indicated.1 Huge variation between countries and regions is observed.2 Underuse leads to maternal and perinatal mortality and morbidity. Conversely, overuse of cesarean section has not shown benefits and can create harm.3 In rural area of sub-Saharan Africa, cesarean rates are 1%–2%, but in Egypt and Greece, the frequency is more than 50%. High cesarean section use is observed among low-risk births, especially among more educated women in, for example, Brazil and China.2 Maternal request is one cause of high cesarean rates, but also intrapartum cesarean section rates are much higher than medically indicated. In China the cesarean section rate is 45%4; close to 2/3 of urban women give birth by cesarean section and 25% in rural areas. A marked reduction in cesarean section rates was observed in an urban tertiary care center in Shanghai as a result of efforts to reduce the high rate of caesarean delivery. No notable differences in neonatal outcomes were observed.5 Cesarean section rates higher than 10% are not associated with reductions in maternal and newborn mortality rates.6 Cesarean section is associated with an increased risk of uterine rupture, abnormal placentation, ectopic pregnancy, stillbirth, and preterm birth in subsequent pregnancies.7 Avoiding the first cesarean influences delivery mode in subsequent deliveries. WHO recommends that every effort should be made to provide cesarean sections to women in need, rather than striving to achieve a specific rate.8 Efforts to lower cesarean section rates are multiple, including policy change, patient education, and physician training.

Caesarean section in the second stage of labor has highest risk for complications and at low stations operative vaginal delivery is a safe alternative. Precise diagnosis of labor progress is essential for optimizing appropriate interventions at the right time. There is an underuse of assisted vaginal deliveries in many countries,9 and more operative vaginal deliveries will reduce the rate of cesarean deliveries and will have pediatric and maternal benefits. Indications for an operative vaginal delivery are prolonged second stage of labor, suspicion of immediate or potential fetal compromise and shortening the second stage for maternal benefit. The risks and benefits of operative vaginal delivery need to be balanced against those for cesarean delivery. It is crucial to know fetal position before the use of forceps, and also before performing manual rotations of the fetal head. In vacuum extractions, the cup should be placed as close to the flexion point as possible; thus, the position of the fetal head should be assured. The risk of vacuum failure is only 2% in a fetus in occiput anterior position at a low station.10

The most common indications for cesarean section during labor are labor dystocia and fetal distress. Labor dystocia is often diagnosed on a subjective impression of the responsible birth attendant. Clinicians should pay attention to the cause of slow progress, which can be due to insufficient contractions, fetal maternal disproportions, or malpositions. Occiput posterior position occurs in around 30% of cases in early labor; however, most fetuses will rotate spontaneously.11,12 Only 7% will be in occiput posterior position at delivery. However, persistent occiput posterior position is associated with complicated deliveries. Little attention is paid to labor mechanisms in contemporary obstetrics. The human fetal head is large related to the maternal pelvis. The cardinal movements are essential for the fetus to pass through the birth canal. The first cardinal movement is flexion, followed by rotation, deflexion, and at last rotation for the shoulders to pass. These processes are complicated and impossible to reliably examine with our hands. Therefore, ultrasound can help clinicians understanding labor mechanisms and labor progression.

Few centers use ultrasound routinely during active labor. Fetal position and station can be examined with ultrasound. It has been shown in many studies that ultrasound is more accurate than clinical examinations13–16; however, the use of intrapartum ultrasound has not shown to reduce cesarean section rates yet. Ultrasound may assist the clinicians to make more precise diagnosis and to objectively confirm the diagnosis of labor dystocia. New studies are needed at large hospitals. The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) published practice guidelines for intrapartum ultrasound in 2018.17 The recommended indications are as follows:

  • Slow progress or arrest of labor in the first stage
  • Slow progress or arrest of labor in the second stage
  • Ascertainment of fetal head position and station before considering or performing instrumental vaginal delivery
  • Objective assessment of fetal head malpresentation

Ultrasound is easy to learn, especially transabdominal scanning showing position will be easy to learn by inexperienced ultrasound examiners. A study from France showed that the learning and accuracy of the determination of fetal head position in labor were easier and higher with transabdominal sonography than with digital examination.18 The probe should first be placed transversely; thereafter longitudinally. The most important landmarks are the fetal face and eyes in occiput posterior position and the cervical spine in occiput anterior position (Fig. 1). Other landmarks are the midline cerebral echo for occiput transverse and the choroid plexuses that are diverging toward posterior and are useful landmarks at low stations.

Figure 1
Figure 1:
Fetal position can be diagnosed using longitudinal transabdominal scanning. A A fetus with the face upward (occiput posterior position). B The fetal cervical spine directed up (occiput anterior position).

Fetal station can be examined using transperineal scanning. The two most used methods are angle of progression and head–perineum distance. The techniques are described in detail in the ISUOG guidelines.17 Correct determination of head position and station is crucial before an instrumental delivery. Ultrasound images should be stored in the medical records. It is important to have objectively documented results in case of litigation.

Intrapartum ultrasound should not replace clinical examinations, but can be used as a complementary tool. It should not undermine the skills of birth attendants. Ultrasound can supplement clinician's skills and help them to improve their clinical practice.

In conclusion, ultrasound should be implemented as a diagnostic tool in labor and used in women with slow labor progress. The ultrasound techniques are easy to learn and understand, and can also be used by nonexperts. Ultrasound will improve clinicians’ understanding of the labor progression. The use of ultrasound in active labor has the potential to diagnose the cause of slow labor progress and to reassure clinicians when it is safe to perform an operative vaginal delivery.



Conflicts of Interest



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