The little fella in the first picture is a 6 weeker, measuring in at 9 mm. This makes him about the size of a kidney bean. The first reliable ultrasound sign of pregnancy is visualization of the gestational sac, seen here surrounding the fetus. Potentially, the sac can be visualized at 4.5 weeks menstrual age when the sac's mean diameter should be about 2.5 mm.
In the second picture, our little bean has grown substantially and is now 18 weeks old. At this point, all major structures are easily visualized, and no abnormalities are present. It's all systems go, and T-22 weeks to launch.
Endovaginal sonography (EVS) has been available since the mid 1980's and has led to substantial improvements. Earlier and more accurate diagnosis of ectopic pregnancy and embryonic demise are possible. EVS has also reduced the need for serial sonography in first trimester diagnosis. Other important goals of first semester sonography:
Forward to Case 19: Fetal Viability
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