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SUBJECT: Obstetric Ultrasound Exams

SECTION: OB Ultrasound   


REVIEW DATE: March 1, 2014

Scheduling: One every 60 minutes. Patients pregnant with multiples are allowed 60 minutes for each fetus (if necessary).

Prep: Full urinary bladder for second trimester screening ultrasound exams on patients that are 20 weeks gestation or less. If a vaginal ultrasound is performed the patient is asked to empty her bladder.

Equipment: Real-time ultrasound unit with 3.5 to 5.0 MHz abdominal ultrasound transducers. It may be necessary to have a unit with a 2.5 MHz transducer. If a vaginal sonogram is performed a 5 to 7.5 MHz vaginal ultrasound transducer is used.  

Exam Protocol: Fetal ultrasound should only be performed when ordered by medical staff (physician, midwife, physician’s assistant, or nurse practitioner).  The lowest possible exposure settings and Doppler settings (when necessary) should be used to obtain the diagnostic information needed. To confirm fetal life with real-time ultrasound, fetal cardiac activity and / or fetal movement need to be observed. 

First Trimester: Evaluate the uterus and adnexa for a gestational sac and its location if seen. If an embryo is seen the crown-rump length is measured.  Report whether or not cardiac activity is seen.  Evaluate the uterus, adnexa, and cul-de-sac.  

Second and Third Trimester: Evaluate fetal life, presentation, activity, and fetal number. Evaluate the amniotic fluid volume as decreased, normal, or increased (an amniotic fluid index is performed whenever there is a question of decreased or increased amniotic fluid volume).  Evaluate the placenta for location and relationship to the cervix, as well as grade and any structural abnormalities. To assess gestational age the following measurements are performed: BPD (biparietal diameter) - measured at the level of the thalamus; HC (head circumference) – measured at the same level as the BPD, around the outer edge of the calvarium; FL (femur length); HL (humerus length); AC (abdominal circumference) – measured transversely at the level of the stomach and of the junction of the right and left portal veins; EFW (estimated fetal weight) and interval fetal growth parameters can be calculated using the previously mentioned fetal biometric measurements. The uterus, adnexae, and cervical length are evaluated. The second trimester screening ultrasound exam evaluates, but is not limited to, the following fetal anatomy:  intracranial anatomy to include the cerebral ventricles, choroid plexus, midline falx, and cavum septi pellucidi; the posterior fossa (cerebellum and cisterna magna); upper lip; 4-chamber view of the heart and the position of the heart within the chest, with an attempt made to image the outflow tracts of the heart; spine; stomach; kidneys; urinary bladder; umbilical cord vessel number and fetal cord insertion site; the anterior fetal abdominal wall; fetal limbs; and nuchal fold. Other areas of fetal anatomy are evaluated as necessary and / or as fetal position permits.

Imaging Protocol:  Even though only specific images are documented on film, a second trimester screening ultrasound exam is performed as described above. The following images represent the second trimester screening ultrasound exam. Additional images may be necessary for proper documentation.

  1. Longitudinal cervix
  2. Lower edge of the placenta and its relationship to the internal cervical os
  3. Longitudinal placenta
  4. Transverse placenta
  5. Placental cord insertion
  6. BPD
  7. HC
  8. AC
  9. FL
  10. HL
  11. Nuchal fold
  12. Width of cerebral lateral ventricular atrium
  13. Transverse cerebellar diameter
  14. Choroid plexus
  15. Cisterna magna
  16. Midline falx
  17. Cavum septi pellucidi
  18. Upper lip
  19. Nasal bone length
  20. Stomach
  21. Urinary bladder
  22. Four chamber heart
  23. RT and LT cardiac outflow tracts
  24. Umbilical cord vessel number
  25. Fetal cord insertion
  26. Kidneys
  27. Spine: cervical, thoracic, lumbar, and sacral
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