When does fetal heartbeat begin?
Fetal heart development typically begins in the third week of gestation. The heart starts beating in the fifth week, which is defined as only week three in terms of fetal age. Note that when it comes to calculating pregnancy length, there’s a significant difference between gestational age and fetal age.
- Gestational age: It represents the number of completed weeks since the first day of your last menstrual period (LMP). It’s a popular method used by doctors that technically includes 2 weeks of time before the mother actually became pregnant.
- Fetal age: Alternatively, fetal age is determined by the tentative day of conception, and is approximately 2 weeks shorter than the gestational age.
For the purposes of this discussion, we will refer only to the gestational age of pregnancy.
Read more: How Long Is a Full-Term Pregnancy?
When can you hear fetal heartbeat?
Even at the 5-week mark, the sound emitted by your baby’s heartbeat is much too faint for detection. At around 8 to 9 weeks, it may still be irregular and slightly difficult to pick up. Your doctor can usually zero in on a steady heartbeat by week 12.
Can you hear fetal heartbeat with a stethoscope?
You may have to wait quite some time before hearing anything with a standard doctor’s stethoscope. Here are two pieces of equipment specifically designed to pick up the fetal heartbeat:
- Fetal Doppler: A handheld ultrasound device using the Doppler effect to create an audible simulation of the heartbeat via a loudspeaker or earpiece. It’s ideal for early detection, when the pregnancy is approximately 9 to 10 weeks along.
- Fetoscope or fetal stethoscope: A structurally modified device which can amplify the fetal heartbeat in the 20th week of pregnancy and beyond.
Why you may not hear fetal heartbeat
The fetal Doppler does in fact have the capability to catch your little one’s heartbeat in the first trimester. But there are times when your doctor is unable to spot it on the ultrasound right away. In most cases, there’s no need to worry as there are multiple explanations.
- Too early in the pregnancy: Gestational age is occasionally inaccurate due to irregular periods, and you might not be as far along in the pregnancy as you think.
- Uterus shape: The shape and orientation of your uterus directly impact the ease of detection. A tilted uterus, for example, could make it tougher for the fetal Doppler to do its job.
- Fetus is out of range: Early on, your baby might be far too tiny for their heartbeat to be definitively recorded by such devices.
- Mother’s weight: If your body mass index (BMI) is more than 25, a layer of abdominal fat is likely preventing the fetal Doppler or fetoscope from catching the heartbeat. In these instances, a transvaginal ultrasound is a good alternative.
Causes of irregular fetal heartbeat
Average fetal heartbeat is between 120 and 160 beats per minute, but tends to be higher during the first trimester. If your doctor notices an irregular heartbeat (or fetal arrhythmia) at a routine prenatal visit, it can mean one of the following:
- A higher than usual heartbeat (tachycardia)
- A slower than usual heartbeat (bradycardia)
- An irregular (or ectopic) rhythm
Fetal arrhythmia happens in only 1 to 2 percent of pregnancies, and is considered a benign condition. More often than not, the problem resolves on its own. The underlying causes of an irregular fetal heartbeat include:
- Caffeine and nicotine consumption: High levels of caffeine and nicotine are sometimes responsible for an increase in fetal heart rate.
- Structural changes in second trimester: This is when your baby’s heart undergoes structural development, leading to mild and temporary irregularities.
- Congenital heart defects: In very rare instances, it’s an indication of structural issues in the fetus’ heart. This is a potentially serious condition that requires further testing and diagnosis by a medical professional.
Should an irregular fetal heartbeat be detected, it’s wise to closely monitor the condition for the next several weeks.
Hearing the precious sound of your baby’s heart beating for the first time is a thrill for any parent. The first fetal heartbeat typically remains undetectable until somewhere between weeks 9 and 12. In rare cases, the absence of a heartbeat may signal a possible miscarriage, but only when accompanied by other early miscarriage symptoms.
There’s no need to be alarmed if your doctor picks up an irregular fetal heartbeat during an examination. Fetal arrhythmia is generally harmless and could disappear over the next few weeks. You will only have to take further action if the condition persists.