Early Pregnancy Fetal Heart Beat – Now you see it, now you don’t

Images and text Genevieve Carbonatto

PV bleeding in early pregnancy is common. This is probably one of our most common presentations to the emergency department. Transabdominal ultrasound is less  sensitive  in the first trimester pregnancy  as  transvaginal ultrasound. Seeing a  fetal heart beat confirms fetal viability.

The following 3 ultrasound cases will focus on this.

This is the ultrasound of a 7 week (by dates) pregnant lady. No previous formal ultrasounds done.

There is  an intrauterine gestational sac

By zooming in on the gestational sac, we have an intrauterine pregnancy which measures 1.08 cm


We then focus on the fetal heart

Do you see a fetal heart beat? At times it looks like there might be one, at times you can’t see it. It is a little like the picture at the start of this post, like a visual illusion. Keep in mind that you have seen and measured a substantial fetal pole and you might be wanting very much to reassure this lady that her pregancy is viable. There is what appears to be motion within the fetal pole, but is this motion a fetal heart beat or is it transmitted from maternal blood flow, from her heart beat and  respiration or from fluid moving within the maternal bowel?  There is in fact no heart beat and it is not possible to put an M mode through the heart to measure  it. Does this mean there really isn’t one? No. All you can say is that with transabdominal ultrasound you cannot adequately display the fetal heart beat and that there is an intrauterine pregnancy but a transvaginal ultrasound will determine fetal viability.

On transvaginal scan an absent heart beat was confirmed

The following case is of  7 weeks pregnancy by dates. The patient presented with PV spotting.

A fetal heart beat is clearly visualised.  A small regular flicker can be seen in the fetal pole.


M mode enables the calculation of the heart beat. It is 144 bpm. The M mode cursor is placed through the heart and the regular flicker of the heart beat can clearly be seen on the M mode trace.

The following patient presents with PV bleeding.

M mode again confirms  fetal cardiac activity.













Teaching point: Be careful when confirming a heart beat in an early uterine pregnancy on a transabdominal scan. If you cannot get an adequate M mode which demonstrates the heart beating then you have not identified a heart beat. Confirmation with a formal transvaginal scan should be organised as soon as possible.


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