pause in fetal heart rate

i am 27 weeks pregnant and at my last prenatal visit with my doctor we noticed that at irregular intervals the hart would pause for about the length of one beat. eg 5 beats pause 3 beats pause 7 beats pause. he has scheduled a ultrasound but i am slightly worried as i dont remember his happening in my first pregnancy. what could be causing this?

[Jeffrey R Boris, M.D.]

Dear 27 Weeks,

Without evaluating your baby's heart, I cannot say for sure exactly what it happening here.  However, the most likely event is that your baby's heart is experiencing isolated premature atrial or ventricular contractions, which are arrhythmias (abnormal heart beats)..  These are single early beats that can happen and reset the electrical system of the heart early.  These are quite frequent during the second trimester and usually disappear during the third trimester or soon after birth.  As long as they are isolated, they do not cause any problems.  It only becomes a problem if there are sustained arrhythmias that last for a while and adversely impact the heart's normal function.