First Trimester Ultrasound

Questions What Measurement is the most accurate for ultrasound dating? In what order do fetal structures appear? What are the 7 items to document in 1st trimester ultrasounds?

Objectives Review the indications for first trimester ultrasound Discuss utilization of ultrasound and laboratory data in the evaluation of first trimester bleeding Review measurements and how they apply to dating criteria Discuss how to document a first trimester ultrasound in the medical record

Indications Dating of pregnancy Size vs dates discrepancy; multiple gestation determination *(1st 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 1st 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 Embryonic Crown-Rump Length (CRL) 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 Embryonic Crown-Rump Length (CRL) Measurement of a CRL with fetal cardiac activity is the best measurement for dating purposes

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.

Determination of Gestational Age Gestational Age (weeks) Sac Size (mm) CRL 4 3 5 6 14 7 27 8 29 15 9 33 21 10 31 11 41 12 51 13 71

The Early Gestational Sac

Early Embryo

The Crown-Rump Length

Late 1st Trimester—10 week

Early Pregnancy Failure Failure of appropriate interval growth by u/s 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

Rapidly Rising Quant β HCG Identifying multifetal gestation Identifying gestational trophoblastic disease Don’t forget lab error (i.e. normal pregnancy in your differential)

Multifetal Gestation

Other applications Evaluation of gynecologic structures Uterus—position, fibroids Adnexae—masses, corpus luteum Early screen for chromosomal anomalies Nuchal translucency measurements

Documentation Whether obtained abdominally or vaginally, the following information should be obtained and documented: Presence or absence of IU gestational sac and identification of an embryo if possible Fetal number Presence or absence of fetal cardiac activity Crown-rump length Evaluation of uterus and adnexal structures and presence of free fluid

Final Pearls Do not include the yolk sac with the CRL Practice, practice, practice Abdominal and Vaginal If you are not sure it is an IUP, get help

What Measurement is the most accurate for ultrasound dating? Crown Rump Length – Up to the 12th week of life.

In what order do fetal structures appear? Gestational sac – 4 to 5 weeks Yolk sac – 5 to 6 weeks Fetal pole - 6 to 7 weeks Cardiac Activity - 6 to 7 weeks.

What organ, what anatomic view? Normal or abnormal?

What organ, what view? Normal or abnormal?

What are the “lucky #7” components of a first trimester ultrasound again?

Components of documentation of a first trimester ultrasound #1: IUP or no IUP #2: how many fetuses #3: FCA or no FCA #4: CRL #5: uterine masses #6: adnexal masses #7: free fluid 27

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