On Friday September 23, 2005, we had the 20 week ultrasound. Luckily, they were able to do the 4d ultrasound (4d is 3d + movement the fourth dimension is time) I was hoping for. Here is a shot of the 4d ultrasound. The baby is lying against the placenta here; you are looking at the side of the baby's face. Click on it for a larger version.
4d Ultrasounds tend to still be pretty noisy (appears as bumps on the surfaces) at this stage. Keep in mind that the image you're seeing are of a tiny 14oz body taken through layers of tissue and liquid. Given that, it's pretty amazing to me that they are able to get as good a shot as they do.
Of course, they did the normal 2d ultrasound as well :-) Normal ultrasound is not just a surface scan, it is a "slice" through whatever is in the path of the wand at that point. For that reason, you see cross sections of the body and skull in the various photos. During the procedure, we actually watched his little heart beating in real time on the monitor. It's pretty neat.
As it turns out, we're having a little boy! Everything checked out, and he looks nice and healthy, and as Melissa would point out, quite active too :-)
During the procedure, the operator (nurse?) took on-screen measurements of key parts of the body and stored them with their records. The software was pretty sophisticated, and served as a great example of a true task-oriented user interface. For example, she pressed a button and several seconds of heartbeat were recorded and the waveform displayed on the screen. She then drew a quick line between two of the peaks and was able to tell a number of things such as BPM. (why BPM wasn't computed automatically is an interesting question for another day). She moved the cursor to another part of the anatomy, pressed another button and a small arrow and the word "boy" was inserted right on the screen. For another measurement, she drew a line from the back of the skull to the front, pressed a button, and then was able to size and elipse that enclosed the cross section of his skull.
From all the data gathered, the system computed age in weeks and days (which was within 2 days of our estimate), as well as weight, body length etc.
Since he wouldn't cooperate and roll over from his stomach, we have another visit scheduled for four weeks from now. They like the baby to be on his back so they can get a better look at the heart. I'm looking forward to more photos and live views.