At about 6 to 7 weeks when an ultrasound is done, one needs to be able to see the flicker of a heartbeat of the fetus. The presence of a heartbeat is a big sigh of relief for the mother. but sometimes when the fetal heart rate is slower than expected during the first trimester of pregnancy, your physician may note that there's some cause for concern and recommend a follow-up ultrasound to check the baby's development.

Why is a slower heart beat a cause for concern?

A slower than expected fetal heartbeat referred to as fetal bradycardia can mean higher odds of miscarriage. Before coming to a conclusion about the future of the pregnancy the Doctor considers testing again in a later week of pregnancy so as to be sure they are not looking at a very early pregnancy due to miscalculation of dates.

Miscarriage Risk

The baby's heart rate should start somewhere around 100 beats per minute around 6 weeks gestation when the heartbeat is usually detected the first time and the heartbeat usually peaks at 9 weeks - sometimes even reaching levels as high as 180 beats per minute and then gradually decrease as the fetus approaches term.

The average fetal heart rate changes during pregnancy. Some doctors consider the lower limit of normal to be:

100 beats per minute up to 6.2 weeks of gestation

120 beats per minute from 6.3 to 7 weeks of gestation

If the fetal heart rate drops below this during the first seven weeks, the risk of miscarriage is seen to increase, with slower rates corresponding to poorer survival.

If the ultrasound reveals that the baby has a slow heart rate,  the parents can get very scared and anxious, especially if one has to wait a week for a followup. Unfortunately, there is no way to tell what is happening without that wait. Sometimes the baby's heart rate will normalize, and then the pregnancy will continue without further complications.

But sadly sometimes the outcome goes the other way. If fetal bradycardia is diagnosed, there is little the mother or the Doctor can do to affect the outcome. Persistent fetal bradycardia is often the result of a chromosomal abnormality that makes it difficult, if not impossible, to bring the pregnancy to term.