Objectives Review the indications for first trimester ultrasound Discuss utilization of ultrasound Review measurements and how they apply to dating criteria Discuss how to document an ultrasound in the medical record

Indications (1 st Trimester) Dating of pregnancy Size vs dates discrepancy; multiple gestation determination * (1 st Trimester)* Vaginal bleeding Abdominal or pelvic pain: rule out ectopic pregnancy/ torsion/ heterotopic pregnancy/ ovarian cyst ***Not credentialed to do*** To confirm viability

Pregnancy Dating with 1 st trimester ultrasound The only utility for “routine” ultrasound as determined by the RADIUS study Early dating is the most accurate (+/- 5-7d or 8%) Better defines timing for later testing and interventions Triple/Quad test Tocolysis/Steroids Reduces the incidence of induction for postdates

Measurements Mean Sac Diameter Should be measured in 3 dimensions May be all that is visible at the discriminatory zone; IUP best confirmed with some fetal element, such as a yolk sac

The Early Gestational Sac
Measurements Embryonic Crown-Rump Length (CRL) Measurement of a CRL with fetal cardiac activity is the best measurement for dating purposes Accurate through the 12 th week of gestation

Late 1 st Trimester—10 week
Typical Measurements There are tables for determining gestational age based on: Gestational Sac Measurement Crown-Rump Length All of the U/S machines at NHP contain software which perform these calculations. The measurements will trigger the gestational age determination.

Early Pregnancy Failure Failure of appropriate interval growth by US of embryo Fetal pole/yolk sac should be seen by the time the MSD is 20 mm (not as accurate as FCA though) Fetal Cardiac Activity should be seen by the time the CRL is 4mm (5mm per AIUM) If not, may repeat the u/s in one week

Rule out ectopic Classic triad—amenorrhea, vaginal bleeding, pain Must have a high index of suspicion Even more so in the face of risk factors Three primary tools for evaluation Physical exam Quantitative β HCG Ultrasound

Lab and Ultrasound Discriminatory Zone—the quant β -hCG level at which one would expect to be able to identify an intrauterine pregnancy For vaginal sonography—1200-1500 (1000-2000 per ACOG) For abdominal sonography—3000-4000 If the quant β -hCG is at or above the discriminatory zone, AND no IUP can be identified, the pregnancy may be ectopic

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