Evaluating FHR in early pregnancy

29 year old G2P1001 presented to ED with vaginal bleeding. Patient reported that she is currently 7 weeks pregnant. She denied any cramping, abdominal pain, nausea, vomiting, fevers or chills. She denied any prior episodes of vaginal bleeding during this pregnancy. Her OB history is non-contributory; delivered NSVD at 39 weeks.

Crown rump length was measured and confirmed fetus age of 7 weeks. Fetal cardiac activity was observed and measured using M mode. FHR was reassuring at 150 bpm. She is diagnosed with threatened abortion.

Doppler ultrasound is currently the standard for measuring FHR in later trimesters of pregnancy. However during the first trimester, there is more precaution surrounding the use of Doppler ultrasound. The first trimester of pregnancy is when rapid cell division occurs, and when there is more potential for damage to the developing fetus. The safety of Doppler ultrasound has not been established during this period. M mode produces less energy and is thought to carry less risk than Doppler. The heart rate is measured from valley to valley on M mode.


-Marly Francois

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