Linear probe in Early Pregnancy

(This post was first published on on July 16, 2016)

Hey all,

Due to the gap between posts as of late, I wanted to do a high-yield/short topic. I also have an extremely special guest, Matt Dawson! I’ve been increasingly using a trans-abdominal linear probe in early pregnancy, and have been avoiding unneccessary trans-vaginal scans.  This is good for patient satisfaction and for increasing patient throughput.  Take a look and let me know what you think!

  1. Are we certain that high frequency high power scanning is safe for these extremely rapidly growing fetal tissues? I have learned in my RDMS studies the principles of ALARA. I was just curious.

    I love your podcasts, btw. It’s really awesome and you are contributing a ton to the evolution of POCUS

    1. Thats a great point. I make sure to have the frequency setting as low as possible, and don’t use doppler to do FHR measurements. The time that it takes for me to look is very brief (<5 seconds) because I'm just trying to find that yolk sac.

      Definitely an important thing to keep in mind.

      Glad you're enjoying the posts!

    2. I agree with Jacob. While ultrasound is generally very safe you are right that we should be aware that as a form of energy it can have effects on tissue and apply the ALARA principle – hence avoid excessive scan times and higher energy functions like doppler. From a frequency standpoint the linear transduce is generally somewhere from 5-12 mHz and the endocavitary transducer is generally 3-9 mHz. They both operate approximately in the same range. And while the endocavitary transducer is positioned up against the cervix and close to the fetus (hence the benefit) the linear transducer is still separated from the fetus by the abdominal wall and anterior uterine wall. So from an absorbed energy standpoint the 2 transducers would be roughly equivalent.

      Jacob, thanks for talking about our paper. It was a great discussion. This technique has been a huge practice changer for us. Keep up the good work.


  2. Interesting point, given the closeness of the endocavity probe, would it be similar? I also love your posts, thanks for all your time and energy!

  3. Nice work
    I sometimes just use the TV probe on the anterior abdo in women with ante vetted uterus and not much subQ tissue. If it’s less than 5 cm to target you get good images often.

  4. Using the linear high frequency probe for indeterminate trans-abdominal scans in early pregnancy is a great idea. I see a tonne of patients with first trimester pregnancy problems, so this could have a significant impact on my practice. Thanks for publicizing it, and bringing it to my attention.

    I had a question – there are no “gyne” presets on our Sonosite’s linear probes. Which preset on the high frequency probe would you suggest to do this study?

    Thanks, Ian.

    1. I tried both the vascular and the nerve preset. The vascular seemed to show movement better, the nerve one looked better overall. Good luck!

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