In early pregnancy ED point of care ultrasound can improve and speed the care of patients with vaginal bleeding, pain or trauma. When evidence of ectopic pregnancy is seen, times to the OR are shorter. When clear evidence of intrauterine pregnancy is seen, patients are immediately reassured and can frequently be discharged to follow up with their OB in the outpatient setting.
INDICATIONS
- Concern for Ectopic Pregnancy
- First Trimester Vaginal Bleeding or Abdominal or Pelvic Pain
- Shock in female patient
- Trauma in pregnancy
- Localization of IUD/Foreign body
- Identify Source of pain in non-pregnant patient
FOCUSED QUESTIONS
- Is there Intrauterine Pregnancy?
- Is there a fetal heart rate?
PREPARATION
- Start with large curvilinear probe (lower frequency, better penetration)
- Can use linear probe to visualize gestational sac.
- For highest resolution, endocavitary probe should be used.
VIEWS
Transabdominal Pelvic – Transverse
This view is obtained placing a large curvilinear probe over the lower abdomen with the probe marker oriented to the patient’s right side. The probe is tilted into the pelvis to visualize the pelvic structures.
Transabdominal Pelvic – Longitudinal
This view is obtained by rotating 90 degrees clockwise from the transverse view. The probe marker should be oriented toward the patient’s head. Again be sure to tilt the probe into the pelvis to visualize the uterus, bladder, cul-de-sac, etc…
Transabdominal Pelvic – Linear Probe
If a gestational sac is seen but no yolk sac is seen, a linear probe may be used transabdominally. In the right patient, this may provide a high resolution view of the endometrial cavity and enable visualization of a yolk sac – which is the criteria we use in emergency medicine to confirm intrauterine pregnancy. This patient has a nice double decidual reaction suggesting pregnancy but the small circle of yolk sac within the gestational sac is the confirmation we are looking for.
Endocavitary Pelvic – Longitudinal
The ultimate high resolution view is obtained with the endocavitary probe. The longitudinal or sagittal view is obtained by inserting the probe with the finger guide at the 6 o’clock position. The probe is rotated counterclockwise 90 degrees. Tilt/Fan the probe to visualize the entire uterus and pelvic structures.
Endocavitary Pelvic – Transverse / Coronal
The transverse or coronal view is obtained by rotating 90 degrees counterclockwise from the longitudinal/sagittal view. Again, tilt/Fan the probe to visualize the entire uterus and pelvic structures.
Intrauterine Pregnancy – Yolk Sac
In emergency medicine the minimal criteria for intrauterine pregnancy confirmation is the finding of a yolk sac. The yolk sac will appear as a small circle within the gestational sac in the uterine cavity.
Intrauterine Pregnancy – Fetal Pole
As pregnancy progresses, a fetal pole will develop along with the yolk sac.
Intrauterine Pregnancy – Fetal Heart
The next evolution is the development of visible fetal heart movement.
Intrauterine Pregnancy – Fetal Movement
The final sonographic finding in early development is actual fetal movement.
Twin Pregnancy
You will see twin pregnancies and beyond. Here we see the sonographer scanning through two gestational sacs with yolk sacs in each.
Measuring Fetal Heart Rate
We measure fetal heart rates with m-mode tracings. This is a lower energy approach compared with pulsed wave doppler. Simply drop an m-mode line through the FH, freeze the image and measure the FH using the calculator in the Mindray measurements setting.
PATHOLOGY
Pseudogestational Sac
This is the reason the minimal criteria for pregnancy confirmation in emergency medicine is the presence of a yolk sac within the gestational sac. Pseudogestational sac may be seen in ectopic pregnancy. The sac here (P) does look irregular. A keen eye will note free fluid in the cul-de-sac.
Fluid in Cul-de-Sac
Molar Pregnancy
Molar pregnancies have the sonographic appearance of a “snowstorm pattern” of many small cysts.
Too Close
This is an important confounder. This appears to be an IUP with fetal pole in gestational sac in the uterus. But, it is actually zoomed in substantially and demonstrates an ectopic pregnancy.
To avoid this, you can:
1) start all scans zoomed out to get a better overview of the entire pelvis and
2) always measure the myometrial mantle. A myometrial mantle measuring > 8 mm likely represents true myometrium with IUP rather than the wall of an ovary / tube / ectopic pregnancy.
RESOURCES AND REFERENCES
References
Early Pregnancy OB Sonoguide chapter
5 min. Sono – Basic OB/GYN scan
5 min. Sono – Intrauterine Pregnancy