Doppler sonography in obstetrics

Cardiotocogram analysis: types of decelerations

Cardiotocography allows evaluation of the fetal heart rate in response to uterine contractions. Normally, early decelerations may occur, mirroring the uterine contraction curve. However, pathological heart rate decelerations are of greatest clinical significance.

Late deceleration (Dip II) Indicates uteroplacental blood flow impairment and progressive hypoxia.

• Relation to contraction: occurs with a significant delay — 30–60 seconds after the onset of the uterine contraction.
• Duration: typically exceeds 1 minute.
• Forms: V-, U-, and W-shaped variants are distinguished.

The severity of the pathological process is assessed not only by the recovery time of the baseline rate and total duration, but also by the FHR deceleration amplitude:

1. Mild degree: amplitude drop up to 15.
2. Moderate degree: decrease by 16–45.
3. Severe degree: drop by more than 45.

Variable deceleration (Dip III) Etiologically associated with umbilical cord pathology. The pathogenesis is explained by vagus nerve stimulation, leading to secondary hypoxia.

• Characteristics: the amplitude varies from 30 to 90, and the total duration is 30–80 seconds or more. The shape of such decelerations is extremely variable, complicating their classification.
• Degrees of severity (by amplitude): mild (up to 60), moderate (61–80), and severe (over 80).

In case of equivocal or pathological CTG patterns, combining the method with direct ECG is recommended. The predictor of hypoxia in this case is the presence of a biphasic ST segment.

Fetal heart rate scoring system in labor

In clinical practice, the G.M. Savelieva scoring system (1981) is widely used. The fetal condition is analyzed using three criteria: baseline FHR, instantaneous rhythm oscillations, and response to contractions or pushing.

First stage of labor

• Baseline FHR: normal is 120–160 bpm. Initial signs of hypoxia manifest as bradycardia (down to 100) or tachycardia (up to 180). Severe hypoxia involves a drop in FHR below 100.
• Instantaneous oscillations: normal is 2–10 per minute. In hypoxia, periodic or persistent monotony (0–2) is observed.
• Response to contraction: normally there is no response, or an increase in oscillation amplitude or early decelerations are noted. With initial hypoxia, short-term late decelerations (20–30 seconds) are recorded, and with severe hypoxia, prolonged ones (31–50 seconds).

Second stage of labor

• Baseline FHR: normal values shift to 110–170 bpm. Severe hypoxia is characterized by a progressive drop in FHR below 100 or tachycardia exceeding 180.
• Instantaneous oscillations: normal is 2–8 per minute. Persistent monotony and pronounced arrhythmia indicate severe hypoxia.
• Response to pushing: normal responses include early decelerations (down to 80 bpm), short-term accelerations (up to 180), or W-shaped variable decelerations (down to 75–85). In severe hypoxia, prolonged late decelerations (down to 50 bpm) and prolonged W-shaped drops (down to 40 bpm) are observed.

Obstetric ultrasound

Ultrasound is the only highly informative, non-invasive, and absolutely safe method for monitoring the embryo and fetus. The study does not require special preparation and is performed transabdominally or transvaginally.

Early diagnosis (I trimester):

• From the 3rd week: the gestational sac (an echo-negative round or ovoid structure) is identified in the uterine cavity. Gestational age is estimated by its mean sac diameter.
• At 4–5 weeks: the yolk sac (a ring-shaped structure) and the embryonic disc—an echo-positive strip 6–7 mm in size—are visualized.
• Determining gestational age: the primary and most accurate parameter in the I trimester is the crown-rump length (CRL).

Assessment of embryonic viability: Cardiac activity begins to be detected at 4–5 weeks. FHR dynamics have a characteristic profile:

• At 5–6 weeks: 150–160 beats per minute.
• At 7–8 weeks: the rate reaches its peak—175–185 beats per minute. Motor activity begins to be detected precisely during this period.
• By the 12th week: FHR smoothly decreases to 150–160 beats per minute.

Fetometry in the II and III trimesters

In the second and third trimesters, the key objective of ultrasound becomes fetometry—measuring anatomical structures to assess fetal growth rates and estimate fetal weight.

The standard protocol includes the following basic parameters:

• Biparietal diameter (BPD) of the head.
• Head circumference (HC).
• Abdominal circumference (AC).
• Femur length (FL).

Class and exam questions

What else to study on this topic

• Detailed analysis of V-, U-, and W-shaped forms of late decelerations.
• Technique for performing direct intrapartum fetal ECG and ST segment analysis.
• Features of transabdominal and transvaginal approaches in ultrasound.
• Algorithm for calculating estimated fetal weight based on fetometry data (BPD, HC, AC, FL).
• Pathogenesis of vagus nerve stimulation in umbilical cord pathology.

Other topics in the "Obstetrics" section

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