During prenatal checkups, doctors usually recommend weekly fetal heartbeat monitoring starting from 36 weeks of pregnancy. What is fetal heart monitoring, how to do it, and why is it necessary to measure contractions?
What is fetal heart monitoring?
Fetal heart monitoring is a simple and painless prenatal test to assess the condition of the fetus. During a fetal heartbeat monitor, the doctor is able to monitor the fetal heartbeat, including what the fetal heart rate is when the baby is resting and when the baby is active, respectively. Your heartbeat speeds up when you are active, and so does the fetus, whose fetal heart rate should speed up when he is moving or kicking.
In most cities in China, if everything is normal during your pregnancy, then your doctor will usually recommend weekly fetal heart monitoring starting from your 36th week of pregnancy. However, if you have pregnancy complications, you may need to start fetal heart monitoring from the 28th to 30th week of pregnancy depending on the situation.
How does fetal heart monitoring work?
For fetal heart monitoring, you should preferably lie on your left side and put a backrest on your back. In some hospitals in China, pregnant women will sit and lean on a chair for fetal heart monitoring, similar to how you sit in a recliner. The fetal heart monitor operator will attach two small pancake shaped devices to your stomach. One of the two pancakes is used to monitor your baby’s heartbeat, and the other to record your contractions. Sometimes, the fetal heart monitor operator may also ask you to press a button when you feel your baby move. Each fetal heartbeat monitoring usually lasts 20 to 40 minutes. The operator can hear the fetal heartbeat and also see it on an electronic screen, while the fetal heart monitor records the contractions on paper.
Why is it necessary to measure contractions during fetal heart monitoring?
There are several reasons why contractions are measured during fetal heart monitoring. First, you may or may not be having contractions during this week of pregnancy. If you do, they may be “false contractions”, which usually do not hurt much, are irregular and infrequent.
Another reason to monitor contractions with a fetal heart monitor is to see if your fetal heart rate changes during the contractions you are having. A contraction stress test will usually check for this. If your baby’s fetal heart rate slows down during contractions, it may indicate that your placenta is in poor condition and that the fetus is having trouble getting oxygen.
How do I read a fetal heart monitor chart?
Many pregnant mothers are confused about how to read the fetal heart monitor chart. In fact, you just need to understand the contractions and the baseline fetal heart rate, and some doctors will also give the corresponding fetal heart monitor score.
The fetal heart monitor is an important part of the late pregnancy checkup, where the mother-to-be can observe the baby’s fetal heart rate to determine if the baby is in good shape. There are usually two curves in a fetal heart monitor chart, the top one records the change in fetal heart rate and the bottom one records the contractions, which the mother-to-be can learn more about in order to understand during the fetal heart monitor. Some doctors will also give a score according to the fetal heart rate monitoring sheet and give advice and suggestions.
1.Fetal heart rate scoring criteria
(1) Baseline fetal heart rate (bpm): 180 beats per minute is 0; 100-119 beats per minute or 161-180 beats per minute is 1; 120-160 beats per minute is 2.
(2) Fetal heart rate variability (bpm): 0 points for less than 5, 1 point for 5-10, and 2 points for more than 10.
(3) Fetal heart rate increase rate (bpm): less than 5 is 0, 5~10 is 1, more than 10 is 2.
(4) Fetal heart rate deceleration: 0 points for repeat late deceleration or repeat variable deceleration; 1 point for variable deceleration; 4 points for no or early deceleration.
The score given by the doctor according to the fetal heart monitoring sheet is according to the above criteria, add up the four scores, if ≤ 4 points means the fetus is hypoxic; if 5-7 points means the situation is suspicious and further monitoring is needed; if 8-10 points means this monitoring response is good.
2.Contractions
According to the frequency of contractions, the contractions can be classified as normal (observed for at least 30 minutes with an average of ≤5 contractions per 10 minutes), or too strong (observed for at least 30 minutes with an average of >5 contractions per 10 minutes).
The contraction curve on the fetal heart monitor indicates the intrauterine pressure, which increases during uterine contractions and then remains around 20 mmHg.
The observation of the contraction curve is very important in determining the fetal heart rate deceleration (which refers to the slowing down of the fetal heart rate when contractions occur). Fetal heart rate decelerations are generally classified as multiple (decelerations accompanied by at least half of the contractions within 20 minutes) and intermittent (decelerations accompanied by less than half of the contractions within 20 minutes). And according to the relationship between fetal heart rate and contractions, it can be divided into three categories: early decelerations, variable decelerations, and late decelerations.
3.Baseline fetal heart rate
The normal range of fetal heart rate baseline is 120-160 beats/min. If the fetal heart rate is <120 beats/min or >160 beats/min for more than 10 minutes, it is called fetal bradycardia or fetal tachycardia.
Fetal bradycardia may be caused by overdue pregnancy, occipital transverse position, fetal congenital heart disease or myocardial conduction defects, and may also be caused by maternal hypothermia, hypoglycemia, hypothyroidism, beta-blockers, etc. It often does not occur suddenly and usually does not require emergency intervention.
In contrast, fetal tachycardia is often associated with maternal fever, infection, fetal anemia or hypoxia, hyperthyroidism, fetal tachycardia, or due to the use of sympathetic agonists or parasympathetic blockers.