What Is Ultrasound?
Ultrasound is a non-invasive, safe method for examining bone and soft tissue structures. Throughout their pregnancy, women receive regular ultrasound imaging to determine the fetal weight, determine placental position, determine the volume of the fluid, and take Doppler readings of the fetoplacental circulation. In the past ten years, it has been employed more frequently to enhance labor management by delivering more precise and repeatable results of labor progress. It can also be used to anticipate methods of delivery using evidence-based algorithms.
What Are the Techniques Employed in Ultrasonography Examination in Labor?
Depending on the factors being evaluated, ultrasound in labor can be conducted via a transabdominal or transperineal technique. Fetal anatomy, presentation, fluid volume, and placental localization can all be assessed during transabdominal imaging. Calculations to establish a suggested fetal head station can be done using transperineal scans, which show images of the fetal head.
Transabdominal: The mother should lie supine with a slight left lateral tilt for transabdominal scanning. The transducer is superior to the symphysis pubis for either transverse or sagittal pictures.
Transperineal: Legs are flexed at the hips in the semi-recumbent position of the mother. The bladder needs to be empty before the scan can begin. The transducer is positioned between the labia majora or at the level of the posterior fourchette. Transperineal ultrasound is a non-invasive method that can be used to anticipate the manner of delivery during labor and has been shown in studies to be able to detect head descent and cervical dilation. During a transperineal ultrasound, the symphysis pubis, pelvic floor muscles, bladder, and indwelling catheter balloon can all be seen as maternal tissues. The maternal structures listed above are shown about the fetal cranium.
How Does Ultrasound Evaluation Help Before Labor or After Admission to the Labor Ward?
Pre-booking evaluations frequently include routine ultrasound scans for expectant mothers in labor before admission. Furthermore, it is also important in low-resource nations with high walk-in rates without antenatal follow-up and poor antenatal care programs lacking sufficient access to ultrasound.
Ultrasound evaluation upon entrance to labor is essential in emergency scenarios such as antepartum hemorrhage and tetanic uterine contractions (long-lasting uterine contractions) to rule out placental abruption, clinical suspicion of uterine rupture, or fetal distress necessitating Doppler tests. With a steadily rising prevalence, induction of labor has emerged as one of the most frequent treatments in contemporary obstetrics. Failure to induce labor carries the maternal, fetal, and neonatal hazards of emergency cesarean sections. It is estimated to occur up to 15 to 20 % of the time, particularly in nulliparous women.
Ultrasound can be used to determine whether women can receive labor induction and have a good chance of success. Ultrasound can be used to establish a woman's eligibility for induction of labor (IOL), as well as for correct gestational age determination, placental and umbilical cord localization, and fetal health evaluation.
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Low-Lying Placenta: A placenta is considered low-lying if covering or lying close to the internal cervical os. During childbirth, a low-lying placenta that has not been properly detected can harm both the mother and the fetus. To locate the placenta, perform a transabdominal ultrasound scan. The outermost edge of the placental membrane concerning the internal cervical os can be used to identify the placenta. Less than 20 millimeters leads to an identification of a low-lying placenta.
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Pelvic Ultrasound Imaging: Women at high risk of surgical vaginal delivery were able to be identified using pre-labor transperineal ultrasound assessment of the maternal subpubic arch angle (SPA), which was also linked to the maintenance of various occiput positions throughout the birth.
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Posterior Cervical Angle (PCA) And Cervical Length (CL): Using CL and PCA measurements, it was possible to independently estimate the period from induction to delivery interval and the result of IOL within 24 hours. The curvilinear transducer is put to the perineum to visualize the internal and external os simultaneously, and the cervical length is then measured as the distance along a line that represents the entire length of the endocervical canal. The posterior cervical angle is determined using the same probe applications as the angle between a line along the cervical canal in the mid-sagittal plane and an additional line tangential to the posterior uterine wall. When the angle is less than 120 degrees, labor is prolonged. The posterior cervical angle accurately measures the location of the cervix. Sonographic measures like cervical length and posterior cervical angle can be used to predict the outcome in women who are having inductions of labor.
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Fetal Presentation: Abdominal palpation during a clinical examination generally has low sensitivity for detecting malpresentation. To determine the fetal presentation, transabdominal ultrasound scanning is employed. The symphysis pubis should be the level where the transducer is positioned in the midline of the mother's abdomen. The internal cervical os, lower uterine segment, and maternal bladder are all visible structures in this image. Knowing how the fetal presenting portion is related to the cervix and the placenta enables accurate viewing of the fetal presenting portion.
What Are the Common Intrapartum Ultrasound Measurements During Labor?
Transperineal intrapartum ultrasound allows for a thorough viewing of fetal and maternal anatomy during labor, which can be difficult to see with transabdominal scanning.
Fetal Head Station: The most significant marker of descent is the fetal head station, which necessitates measuring the head in centimeters concerning the mother's ischial spines. When performing a digital vaginal examination, a station is considered 0 cm deep if the deepest bony portion is at the level of the ischial spines. On the other hand, the benefit of transperineal ultrasound examination is an accurate and repeatable evaluation of the fetal head station. The probe is positioned at the level of the fourchette or between the two labia majora for the transperineal ultrasonography examination.
Caput Succedaeum and Cranial Moulding: Assessment of the fetal head position and station is challenging due to the caput (a soft tissue enlargement) and molding (overlapping of the fetal cranial bones) that can occur during labor. With transperineal ultrasound, its presence can be depicted objectively visually. These characteristics may influence an obstetrician when deciding whether to perform an operative vaginal birth.
How Is Fetal Head Position Determined by Ultrasound Before Instrumental Delivery Helps?
Instrumental delivery is an essential component of obstetric care. It is appropriate for the protracted second stage of labor or fetal compromise or to abbreviate the second stage of labor for maternal causes, including heart, respiratory, cerebrovascular, or neuromuscular disorders.
When there is clinical doubt about the fetal position or before starting an aided vaginal birth, it has been advised to routinely examine the woman using ultrasound. A transabdominal or transperineal sonographic technique can be performed depending on how much the fetal head is engaged.
Correctly determining the fetal head position and applying the tool correctly are crucial components of the successful and safe use of vacuum and forceps. Therefore, the vacuum cup should be placed on the flexing point, and the forceps blades should parallel the sagittal suture. Doing so is related to a high success rate and decreased maternal and fetal morbidity.
Conclusion:
The management of labor and delivery may benefit from ultrasound. A frequent obstetric procedure, labor stimulation is carried out in 20 % of pregnancies. The transvaginal sonography-measured pre-induction cervical length has been demonstrated to correlate significantly with the time from induction to birth and the risk for cesarean delivery. Ultrasonography is an essential tool to perform a safe surgical birth and determine whether a vaginal delivery would be successful.
