First trimester dating ultrasound
Yolk sacs larger than 6 mm are usually indicative of an abnormal pregnancy.
Failure to identify (with transvaginal ultrasound) a yolk sac when the gestational sac has grown to 12 mm is also usually indicative of a failed pregnancy.
The gestational sac does not correspond to specific anatomic structures, but is an ultrasonic finding characteristic of early pregnancy.
Ectopic pregnancies can also have a gestational sac identified with ultrasound, even though the pregnancy is not within the endometrial cavity.
Identify (if present), the gestational sac, yolk sac, fetus (or fetuses), presence or absence of fetal movement and fetal heart beat.
After the uterus is evaluated by sweeping up and down and side to side, the ovaries are identified and evaluated.
These differences rarely effect gestational age dating by more than a day or two.
Yolk Sac As the pregnancy advances, the next structure to become visible to ultrasound is the yolk sac.
Technique First trimester scanning can be performed using either an abdominal approach or a vaginal approach.
Document important views and measurements on film or electronically.
Then document your findings in some written format.
Place a small amount of ultrasonic coupling gel on the tip of the transvaginal transducer. After lubricating the vaginal opening, gently insert the transducer into the vagina.
Visualize the longitudinal plane of the uterus (sagital section) and evaluate its' size.
Failure to identify fetal cardiac activity in a fetus whose overall length is greater than 4 mm is an ominous sign.