What changes occur in the fetal heart rate during pregnancy?

Listening to the fetal heart rate during pregnancy is the use of medical equipment to measure the heartbeat of the fetus in the abdomen. The fetal heart rate also changes during pregnancy. Generally, as the fetus grows, the fetal heart rate will show different degrees of changes. Generally, pregnant women need to be tested at 17-20 weeks. Generally, a fetal heart rate of 120-160 is normal. Pregnant women also need to do regular prenatal checkups so that they can observe the condition of the fetus at any time.

What are the changes in fetal heart rate during pregnancy?

Fetal heart rate

The fetal heart rate is the heartbeat of the fetus, which can usually be heard in the abdomen with a stethoscope between 17 and 20 weeks. The fetal heart rate is 120-160 beats/minute, sometimes faster and less regular. Fetal heart rate monitoring should be performed regularly during pregnancy, which is the main means of correctly assessing the fetal condition in the uterus.

How to read fetal heart rate monitoring chart

Fetal heart monitoring is an important prenatal examination item in the late pregnancy. Expectant mothers can observe the baby's fetal heart rate based on the fetal heart monitoring chart to determine whether the baby is in good condition. The fetal heart rate monitoring chart usually has two curves. The upper one records the changes in fetal heart rate, and the lower one records the uterine contractions. Expectant mothers can learn more about them so that they can see clearly during fetal heart rate monitoring. Some doctors will then give scores based on the fetal heart rate monitoring report and provide opinions and suggestions.

1. Fetal heart rate monitoring scoring criteria

(1) Baseline fetal heart rate (bpm): 180 beats/min is 0 points; 100-119 beats/min or 161-180 beats/min is 1 point; 120-160 beats/min is 2 points.

(2) Fetal heart rate variability (bpm): less than 5 is 0 points, 5-10 is 1 point, and greater than 10 is 2 points.

(3) Fetal heart rate acceleration (bpm): less than 5 is 0 points, 5-10 is 1 point, and greater than 10 is 2 points.

(4) Fetal heart rate decelerations: repeated late decelerations or repeated variable decelerations were scored as 0 points; variable decelerations were scored as 1 point; no or early decelerations were scored as 4 points.

The score given by the doctor based on the fetal heart rate monitoring report is based on the above standards, adding up the four scores. If it is ≤4 points, it means fetal hypoxia; if it is 5-7 points, it means that the situation is suspicious and further monitoring is required; if it is 8-10 points, it means that the monitoring response is good.

2. Uterine contractions

According to the frequency of uterine contractions, they can be divided into: normal (observed for at least 30 minutes, an average of ≤5 times every 10 minutes) and excessive (observed for at least 30 minutes, an average of >5 times every 10 minutes).

The contraction curve on the fetal heart rate monitor indicates the intrauterine pressure, which increases when the uterus contracts and then remains at around 20 mmHg.

Observation of the contraction curve plays a very important role in determining fetal heart deceleration (referring to the slowing of fetal heart rate when uterine contractions occur). Fetal heart rate decelerations are generally divided into multiple (decelerations accompanied by at least half of the uterine contractions within 20 minutes) and intermittent (decelerations accompanied by less than half of the uterine contractions within 20 minutes). According to the relationship between fetal heart rate and uterine contraction, it can be divided into three categories: early deceleration, variable deceleration, and late deceleration.

3. Fetal heart rate baseline

my country stipulates that the normal range of fetal heart rate baseline is 120-160 beats/minute. A fetal heart rate of <120 beats/min or >160 beats/min for more than 10 minutes is called bradycardia or tachycardia.

The causes of bradycardia may be overdue pregnancy, transverse occipital position, congenital heart disease or myocardial conduction defects in the fetus. It may also be caused by hypothermia, hypoglycemia, hypothyroidism, taking beta-blockers, etc. in pregnant women. It often does not occur suddenly and generally does not require emergency intervention.

Fetal tachycardia is often related to fever, infection in pregnant women, anemia or hypoxia in the fetus, hyperthyroidism, fetal rapid arrhythmia, or caused by the use of sympathetic agonists or parasympathetic blockers.