One of the most difficult moments for a patient who has suffered for either infertility or miscarriages is to find out , at the first pregnancy ultrasound ,that something is not entirely normal.
An example of this is when on , one of the early ultrasounds, the heart beat of the embryo ( baby) is observed as being too slow.
Fetal heart rate ( or embryonic heart rate) in
the first trimester depends on the gestational week. It increases since 6 to
9 weeks and decreases after 10 weeks. The highest values of fetal heart rate
are observed between 9 and 10 weeks of gestation. The risk of early
pregnancy loss increases significantly in case of detecting slow FHR.
but what is a normal value for embryonic heart rate / fetal heart rate?
In one study At 6 weeks, mean embryonic heart rate was 116 +/- 21 beats per minute , then slowly increased, reaching mean 172 +/- 9 beats per minute at 10 weeks. At 11 weeks the mean fetal heart rate achieved the level of 165 +/- 7 beats per minute.
Embryonic heart rates below 90 beats per minute at 6 to 8 weeks of
gestation have been shown to be associated with a high
likelihood of subsequent first trimester demise.
what the actual risk of risk of pregnancy loss or miscarriage was quantified in one study as: first trimester survival rate was 61.6% for slow
early heart rates ( less than 100 beats per minute at 6.2 weeks or less , less than120 beats per minute at
6.3 to 7.0 weeks), lower than the survival rate with normal heart rates.
In another study the rates of first-trimester demise were 60.6% for pregnancies with slow
heart rates at 6.0-7.0 weeks), 17.4% for those with
borderline heart rates , and 9.1% for those with normal
heart rates.
As mentioned above boundary between slow and normal heart rates has not been
established,
however, and different studies have yelded different numbers. But these studies suggest that lower limit of normal is 100 beats per minute up to 6.2 weeks' gestation
and 120 bpm at 6.3-7.0 weeks.
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