Role of ultrasound in labor

The article was consulted with Specialist Doctor I Le Hong Lien - Department of Obstetrics and Gynecology - Vinmec Central Park International General Hospital.

Currently, determining the exact time of onset of labor remains a challenge for many obstetricians. In addition to manual clinical examination, labor ultrasound also plays an important role in cases of abnormal fetal position, delayed labor and cessation of progress.

Labor is the process of synthesizing many phenomena to prepare for the birth of the fetus. The most important of which are uterine contractions that help the cervix gradually open and help remove the pregnancy and placenta.
What doctors and midwives usually do is to watch for signs:
Uterine contractions occur frequently, but need to be distinguished from labor contractions. Cervical dilation >3-4cm. Normal labor goes through 3 stages:
Stage 1 (The process of opening the cervix). From the time of labor until the cervix is ​​fully dilated, the average time is 15 hours divided into 2 stages:
Latent stage (8 hours). Active phase (7 hours). Stage 2 (Pregnancy book). From the time the cervix is ​​fully dilated until the pregnancy comes out, the time depends on whether the fetus is a baby or a straw:
Contraception: time from 30 minutes to 2 hours (average 50 minutes). Straw: time out from 15 minutes - 1 hour (average 20 minutes). Stage 3 (Local book). From the time the placenta is delivered to the time the placenta comes out, on average, it takes 5-30 minutes.

Pregnant women will be diagnosed as labor if there are signs:
Intermittent abdominal pain (by labor contractions) Pink vaginal discharge. Cervical dilation. Establishment of the amniotic sac.

In addition, the characteristics of true labor include:
Regular uterine contractions, about 12 per hour. The interval between contractions gradually shortens, increasing in intensity and duration. Intensity increases, proportional to pain. Causes cervical dilation. Down the throne. Antispasmodics also do not stop contractions.

Traditionally, the assessment and management of a labor has been based on physical examination, i.e. manual examination to measure uterine dilation, penetration, and fetal position. However, in some cases, this method can be inaccurate and subjective (eg, with serous tumours), making it difficult to determine the location of the fontanelle and the line of the fetal fontanelle.
Many studies have shown that ultrasound of labor is more accurate than clinical examination in diagnosing the type of pregnancy, the extent of the pregnancy in the pelvis and predicting the termination of pregnancy.
To a certain extent, the role of ultrasound in labor includes:
Determining the option of normal delivery or cesarean section. Prognosis of the outcome of a birth. Abdominal ultrasound: helps to locate the fetal head and spine. Perineal ultrasound: helps to determine the fetal position and penetration. 3.1. Assessment of fetal type It is very important to accurately determine the occipital position of the fetal head (anterior occipital, posterior occipital). Until now, doctors often determine the fetal type through manual examination, palpation of the interfocal, anterior and posterior fontanelle lines of the fetus. Because the posterior occipital position often leads to the possibility of cesarean section and increases the risk to the mother and fetus, it is important to properly assess the fetal position during labor.
If misjudged can prolong labor, increase the rate of trauma for both mother and baby.
Manual examination is often less accurate for fetal abnormalities, e.g. transverse, posterior occipital or large, asymmetrical prolapse (associated with obstructive labor). In this case, surgical intervention is almost certainly required.

3.2. Evaluation of fetal penetration Peripherality is the relationship between the head position in the birth canal relative to the plane through the sitting spine of the pregnant woman. Normally, during a manual examination, the doctor will use his hand to measure the penetration of the fetus through the vagina. At that time, the fetal head is assessed as perforated when the lowest and hardest part of the skull is level with the plane through the mother's 2 pelvic spines (intrusion 0).
3.2. Evaluation of fetal head descent and abduction Ultrasound of labor also assesses angle of progression (AoP, also known as “angle of descent”), which is considered an accurate parameter and assesses head declination. pregnant.
Even a small amount of supine delivery can interfere with stage 1 descent and may lead to abnormal labor. Thus, ultrasound is also useful in assessing the occipital angle (OSA) and predicting labor outcome.
Transabdominal ultrasound is more accurate than manual examination for the anterior or transverse occipital position.

At present, the ultrasound technique of labor has not been widely applied, although many studies have demonstrated higher objective accuracy and reproducibility than manual examination. However, there are 2 cases where ultrasound is definitely used in labor, that is:
Labor slows or stops progressing in stages 1 & 2. When assisted delivery is needed, ultrasound helps to identify any position. Usually, determine the position, orientation of the fetus and the penetration. Note: Labor ultrasound should be considered as an adjunct (when needed) without completely replacing the traditional manual examination.
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