3D Ultrasound and Maternal Body Weight

Jane Foley's picture


Dear Ms. Ultrasound,
I'm currently 24 weeks pregnant with my first baby ( a boy named Caius Smile ). I've already had a "regular" ultrasound at 12 and 16 weeks. Particularly with the 16 week ultrasound, it came back that a few things were suboptimally viewed due to 'maternal body habitus'.

I have been booked for a 25 week ultrasound using a 3D ultrasound machine to try and get a better look at these structures that they have had trouble with.

My questions are: Will the 3D machine have better chances of higher detail/any detail despite maternal body weight? If the results come back negatively again and vaginal ultrasound is not available should I just not worry about getting more regular/3D ultrasounds? Is there anything I can do to help produce better information for the sonographer?

Thanks for your help!

Meg L.


Hi Meg,

Yes, increased body weight always poses a problem for ultrasound. The way an ultrasound image is produced is, we send out a certain amount of ultrasound waves and ultimately would like them all to return to the probe (transducer) and tell us what they have hit -- an echo of sorts.

The best and highest resolution is when we send out lets say 100,000 sound waves (random number) and 100,000 sound waves come back to us. When we have a small body type there is less opportunity for loss of sound waves due to refraction. The more tissue densities the sound must penetrate the higher loss of information. When the sound waves travel a fair distance to the baby, we may only get 50,000 sound waves back, which produces a suboptimal image.

When the sound travels a few centimeters to the fetus, the resolution can be incredible seeing things like the lens of the eye to a tongue sticking out to the valves in the heart.

The 3D uses the same physics, so the imaging is up against the same odds of obtaining suboptimal images.

The vaginal probe can only travel a short distance and is helpful when looking at the cervix at this stage of pregnancy. It is used in the early first trimester as the pregnancy is close to the probe.

There is not really anything you can do to help, short of losing weight. This is not practical in this short interim. Hopefully you are not having any problems and can have an uneventful, healthy pregnancy without the aid of ultrasound.

With Regards,
-- Jane, RDMS