1. First Trimester Ultrasound

2. 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?

3. 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

4. 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

5. 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

6. 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

7. 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.

8. 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

9. The Early Gestational Sac

10. Early Embryo

11. The Crown-Rump Length

12. Late 1st Trimester—10 week

13. 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

14. 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

15. 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— ( per ACOG)
For abdominal sonography—
If the quant β-hCG is at or above the discriminatory zone, AND no IUP can be identified, the pregnancy may be ectopic

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

18. Multifetal Gestation

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

20. 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

21. 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

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

23. 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.

24. What organ, what anatomic view? Normal or abnormal?

25. What organ, what view? Normal or abnormal?

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

27. 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

28. The end 28