by firstname.lastname@example.org (322 Posts), Tue Aug 29, 2006 01:18 pm
Normal fetal heart rate ranges between 120-160 beats per minute throughout most of gestation; toward the end of pregnancy the normal rate may range in the 110-120 rates. It is not unusual for a fetal heart to accelerate into the 160-180 range after movement, articularly in the last third of pregnancy. Such an acceleration is usually transient.
A sustained fetal heart rate above 160 beats per minute can indicate number of things including an inflammatory/infectious condition involving the pregnancy, a fetal heart structural or rate problem, a thyroid condition, possibly a response to what the mother ate/drank/took medicinally, or be idiopathic--"it happened but the significance or cause is unclear". The obstetrician is thinking of these things and making a decision of whether a faster than average fetal heart rate is incidental or something to be followed up further.
A reactive fetal heart rate is a reassuring thing, accelerating 15 beats per minute for 15 seconds or more at or beyond 32 weeks gestation, in response to fetal movement much like an adult heart speeds up when that person changes position or becomes more active.