At approximately three and a half weeks after conception the fetal heart can be seen on an ultrasound. Prior to this stage the structures may be too small to be identified. A gestational sac measurement is taken in three planes and correlates with the gestational age.

 
     
 
 


Taken at the mid-line of the uterus and in the longitudinal plane, show the proper landmarks. If fetal pole is not identified, vaginal ultrasound must be performed. Be sure to annotate MLL for mid-line longitudinal or SAG for sagittal.

Next, scan completely out of the uterus to the right adnexa - then to the left adnexa.

  
 
     
 
 


Next, the probe is turned at a 90 degree angle counter-clockwise to image in a transverse plane. Scan inferiorly to visualize the maternal vaginal canal, then the cervix, then scan superiorly through the uterus and the maternal bladder. The second image is taken at the widest portion of the uterus. If the fetus is not visualized a transvaginal ultrasound is necessary to image within the gestational sac.

 
 
     
 
 


For the purpose of confirming a viable IUP a transvaginal ultrasound is routinely done in the first trimester. The maternal bladder must be emptied. The adnexas must be visualized in order to rule out ectopic pregnancy. Once the gestational sac is identified transvaginally, it is important to zoom up on the sac and scan completely through it. If a fetal pole is not identified, gestational sac measurements should be taken.

  
 
     
 
 


As in a transabdominal scan, the organ must be visualized in two planes, sagittal and transverse. Although the direction of the probe is transverse, in actuality, the cut through the patient is a coronal cut. Turn the probe 90 degrees counter-clockwise. Scan through the entire uterus in the transverse (coronal) plane. The image is taken at the widest portion of the uterus and should reveal the sac.

 
 
     
 
 


The protocol for obtaining gestational sac measurements will vary according to the machine's programmed package. The gestational sac must be measured in three planes. In the sagittal plane, the widest dimensions of the sac should be apparent. Freeze the image. The zoom feature may be utilized for optimal visualization. Select the measurement key, then choose the GS option. The first measurement should be taken at the widest portion from anterior to posterior.

 
 
     
 
 


The second saginal image of the gestational sac should be identical to the first, in order to maintain measuring consistency. Following the steps above, make sure to choose the measurement key again, and the GS option. The second measurement should be taken at the widest portion of the sac from right to left.

  
 
     
 
 


Turn the probe 90 degrees counter-clockwise. Zoom in on the gestational sac. Obtain the image at the widest portion of the sac in the transverse plane. Freeze the image. The zoom feature may be utilized for optimal visualization. Select the measurement key, then choose the GS option. Measurements should be taken from right to left at the widest portion. Print report.