The use of ultrasound during labor can provide a plethora of information to enhance patient safety. Ultrasound sheds light on maternal and fetal conditions alike, allowing obstetricians to more effectively manage complications in the labor and delivery unit.
When Patients in Labor Should Receive an Ultrasound
The latest clinical practice guideline from the World Association of Perinatal Medicine (WAPM), published in Perinatal Journal in 2022, calls ultrasound at admission for labor "an integral part of the pre-booking assessment." This imaging is particularly important in resource-poor settings where prenatal care is basic and may not include quality ultrasound imaging or where patients may not have received adequate care for other reasons. In these scenarios, ultrasound can identify previously unknown potential complications.
ISUOG Recommendations for Ultrasound in Labor Focus on Head Position
While International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) practice guidelines state that they do not recommend ultrasound in labor as a standard of care, they stress instead that imaging is sometimes clinically indicated and can guide labor management. The ISUOG guidelines focus on the identification of head position as a potential complication of labor and outline the importance of determining head position, given best practices for imaging.
To determine whether ultrasound could accurately determine fetal head position, the ISUOG reviewed studies published between 1966 and 2017. Their review found ultrasound to be superior to digital examination in determining fetal head position, station, descent and attitude. In fact, studies showed that digital palpation of the fetal head position was subjective and that inaccuracy ranged from 20% to 70%. The studies also revealed that patients prefer ultrasound over digital examination during labor.
Based on these findings, the ISUOG gives four indications for performing ultrasound during labor:
1. Slow progress or arrest of labor in the first stage
Studies reviewed for the ISUOG guidelines found that in women with prolonged first-stage labor, head-perineum distance (HPD) and angle of progression (AoP) in the first stage of labor were good predictors of the need for cesarean delivery. The likelihood of a cesarean grew exponentially as the HPD increased to more than 50 mm and the AoP was less than 100°. Both HPD and AoP are determined via transperineal ultrasound. The occiput-posterior position was also associated with an increased risk of cesarean delivery. The fetal position can be ascertained through transabdominal ultrasound during labor in the sagittal and transverse planes.
2. Slow progress or arrest of labor in the second stage
Although ISUOG found fewer studies addressing head position in the second stage of labor, one smaller study found that a head-up position was associated with 80% successful spontaneous vaginal delivery compared with downward or horizontal. The head position is visualized by transabdominal ultrasound.
3. Ascertainment of fetal head position and station
The accuracy of digital palpation of the fetal head position ranged greatly, but inaccuracies were higher when the head was not in the normal position. An incorrect assessment of head position during an instrumental delivery can not only lead the procedure to fail but also cause injury to the fetus and parent. Head station and position are best assessed by transabdominal ultrasound, while direction should be determined by transperineal imaging.
4. Objective assessment of fetal head malpresentation
Again pulling from previous studies, ISUOG found that head malpresentation as assessed by either transabdominal or transperineal ultrasound may be a cause of prolonged first-stage labor. A malpresentation of the fetal head can result in a higher risk of delivery by cesarean section as well as complications in the carrying parent and child.
Ultrasound During Labor To Support Other Diagnoses
The WAPM describes ultrasound during labor as an essential tool for triaging patients who arrive for admission experiencing emergencies such as hemorrhaging, placental abruption or a ruptured uterus. An ultrasound can provide a swift diagnosis and a faster path to treatment.
Ultrasound Before Induction of Labor
Labor inductions can be used for a variety of reasons, but there are several conditions identifiable on ultrasound that contraindicate labor induction. StatPearls lists these as vasa previa or placenta previa, transverse fetal presentation and umbilical cord prolapse. StatPearls also recommends obtaining a Bishop score before labor induction, noting that a successful vaginal delivery can be expected if the score is eight or above.
Postpartum Ultrasound Examination
In the postpartum period, the WAPM suggests that ultrasound can take on several roles. These include scanning for placental remnants when hemorrhage is present, assessing the need for curettage, excluding uterine rupture in vaginal birth after a cesarean, retention of blood after a cesarean and assessing birth-related trauma.
A Note About Infection Control for Ultrasound During Labor
The ISUOG cautions that contaminated gel can be a source of infection in patients who have an ultrasound in labor and go on to have a surgical delivery, either by cesarean or vaginally. They recommend that if single-use containers are unavailable, then the gel container should never make contact with the patient's skin or the transducer probe to avoid contamination. It is also important that practices follow the manufacturer's recommendations for cleaning and disinfecting ultrasound devices.
Ultrasound in labor may not be appropriate for every patient, especially those who are low risk. However, it has a clear continuum of opportunity from the time the patient arrives through discharge. Whether labor is not progressing as normal or a patient is scheduled for induction, performing an ultrasound may help to reduce potential complications and improve patient safety in labor and delivery.
Learn more about the benefits of postpartum ultrasound HERE.
