Forum 1st trimester

Does an external ultrasound measurement differ from an internal one?

3 replies

Butterfly37
Hi ,

Does anyone know if what my midwife says is true: that an external measurement from a 7-week ultrasound gives a different result than an internal one?

Replies

  1. Beagle #2

    What I understood from my doctor is that at that stage, internal measurements are much more reliable. With me, they did an external scan at 8 weeks and then pushed the due date forward by a week at 12 weeks. A few millimeters can make a difference of a week at that stage.

  2. Butterfly37 started this #3

    So with Beagle, at 8 weeks, did they do an external ultrasound and estimate you were a week behind?

    Here's how it is with me.
    I had my ultrasound yesterday at 7 weeks. They started with an external scan. They immediately saw a gestational sac with a clearly beating heart. The baby just seemed smaller. But since it was external, she wanted to do an internal scan to measure it properly.
    But internally, there was hardly anything to see. Only, an internal scan revealed a 2nd gestational sac with a yolk sac in it, and you could see something else, but it was very unclear. The only way to clearly see the beating heart was externally in the first gestational sac. But she didn't want to measure it that way because that would be different from measuring via an internal ultrasound.

    So my question is whether that's really true.
    Does the baby look smaller externally and therefore get a lower CRL measurement because it's not measured properly?

    It's quite remarkable that it was hardly visible internally, while you could see the heartbeat directly externally.

  3. Beagle #4

    Hmm, I'm not sure if it makes a huge difference. I found the external ultrasound quite unclear. With my daughter back then, I had an internal one at 8 weeks, and I found that much clearer. But even then, I was a few days ahead with the 12-week scan.

    The 8-week scan matched my calculation, but the 12-week one didn't really. This time I didn't use ovulation tests, so I don't know exactly when I ovulated. With my daughter, the 12-week scan didn't match my ovulation at all.

    I wonder if earlier scans are harder to measure? Did it make a big difference in the number of days you calculated yourself? Are you getting another scan soon?

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