Transabdominal

Clinical Indication

Pregnant and bleeding, pelvic pain in pregnancy, cessation of fetal activity

Probe Selection

Curvilinear

Additional Views and Measurements

  • Measure fetal heart rate (FHR)
  • Measure biparietal diameter (BPD) to calculate GA
  • Measure femur length (FL) and calculate GA

Tips

  • Do NOT have the patient urinate first, the bladder makes an excellent echogenic window for visualizing the pelvic structures. 
  • Do NOT use spectral doppler modes as it exposes the fetus to increased energy levels which may be harmful- Use M-mode to measure the FHR.
  • The bladder may produce edge artifact that will obscure structures of the cervix or uterus.
  • When measuring the BPD make sure your image contains the axial view (same as a head CT) of the cavum septi pellucidi, paired bilateral thalami and quadrigeminal cisterns. HINT: the thalami will form the shape of a butterfly! 
  • The BPD should be measured from the outer wall of the near-field calaverium to the inner wall of the far-field calaverium. 
  • A pregnant patient involved in trauma should have an ultrasound to evaluate for fetal motion, fetal heart rate and free fluid. 
  • Always get a RUQ and LUQ view with a suspected ruptured ectopic to evaluate for free fluid. 
  • Beware the cornual and cervical ectopics! The can appear just like IUP’s! Make sure there is at least 8mm of myometrium between the GS and the outer layer of the uterus.

Transvaginal

Clinical Indication

Pelvic pain, bleeding in 1st trimester, abdominal pain in 1st trimester

Probe Selection

Endovaginal (aka Endocavitary) 

Additional Views and Measurements

  • Left and Right adnexa, with measurements of the ovaries 
  • Crown-Rump Length (CRL) measurement to calculate GA
  • FHR using M-Mode (Again avoid the spectral Doppler modes to use as little energy as possible) 
  • Measurements of ovarian cyst (Remember a “cyst is simply a follicle that is >3cm) 
  • Cervical length (comment if os is open or closed) 
  • RUQ and LUQ views to evaluate for free fluid

Tips

  • Make sure you have the patient urinate first! A full bladder will obscure your views and it will be uncomfortable for the patient.
  • There are 2 ways to orient the transvaginal probe (Always use your Right hand, even if you are a lefty): (1) Hold it like a cop holds a gun (with the indicator marker pointed at the ceiling)-This will give you your sagittal images of the uterus (long axis views). (2) From the “Cop” orientation, twist your hand counter-clockwise, so the indicator is pointing to the patient’s right thigh (similar to how a ‘Gangster’ holds a gun-this will give you your coronal images of the uterus and this is the orientation to find the adnexal structures. Using the “Cop” and “Gangster” orientations as general guidelines, you may have to deviate as the pelvic structures do not always lie in the perfect planes.
  • A retroverted uterus will curve the opposite way (usually toward the right side of the screen when the indicator is on the left) and can throw off your “normal” views. 
  • Do NOT use spectral doppler mode as it exposes the fetus to increased energy levels which may be harmful- Use M-mode to measure FHR. 
  • The adnexal can be difficult to locate-Obtain a coronal view of the uterus and trace the side to the cornual flare, then walk along the fallopian tube (if visualized) until the ovary appears. Use the iliac vessels as your landmark, the ovary should be located just anterior to them.
  • A yolk sac within a gestational sac is definitive of an IUP, excluding cornual and cervical ectopics. Note that the YS will disappear around 10-12 weeks.
  • Beware of the “pseudogestational sac” when evaluating for an ectopic pregnancy.
  • Use color doppler on the ovaries to demonstrate adequate blood flow, especially when torsion is part of the differential. 
  • If you are having difficulty visualizing the pelvic structures, you can use your free hand to apply gentle pressure on the lower abdomen to bring into view the pelvic structures.
  • Always try to view the uterus in the transabdominal approach first. It is less invasive and women may be further along than they think. 
  • When ectopic is part of the differential, look in the splenorenal recess and Morrison’s pouch for free fluid. 
  • A cornual ectopic can look like an IUP, always confirm there is at least 8mm of myometrium surrounding the gestational sac and the GS lies within the endometrial stripe. 
  • Likewise a cervical ectopic can look like an IUP, but lies very close to the cervix, when in doubt, get a comprehensive U/S.
  • To calculate GA from the GS measure LxWxH of the GS, the machine should have a calculator to aid you.
  • After ~12 weeks, use BPD and femur length to age the embryo, CRL is not well validated beyond the 12 week mark.