1. Fetal Ultrasound Measurement
PREPARED BY:
OMAR ABOUSOUD PGY-3
ALEJANDRO HEFFESS MD

2. INDEX FIRST TRIMESTER …. Slides 3-9 - Yolk Sac …. Slide 5
- Terminology and Diagnostic Tests Used Early in the First Trimester …. Slide 6
- Diagnosing Pregnancy Failure Using the Transvaginal Probe …. Slide 7
- Diagnostic and Management Guidelines Related to the Possibility of a Viable Intrauterine Pregnancy in Women with Pregnancy of Unknown Location … Slide 8
- First Trimeseter FHR and Nuchal translucency …. Slide 9
SECOND AND THIRD TRIMESTERS …. Slides 10 – 18
- Various Important 2nd/3rd Trimester Measurements …. Slides 12-18
 Cervix/Placenta …. Slide 12
 Fetal Intracranial Measurements, Nuchal Fold and FHR …. Slide 13-14
 Fetal Renal Pelvis …. Slide 15
 AFI …. Slide 16
 Growth Parameters (IUGR, LGA, Macrosomia) …. Slide 17
 Echogenic bowel, Echogenic Intracardiac focus and Fetal pericardial effusion …. Slide 18
Dating Error: When to Revise the EDD by U/S Parameters? …. Slide 19
References …. Slide 20

3. FIRST TRIMESTER

4. First Trimester
Age based on fetal CRL on the first trimester ultrasound is the most accurate estimation of fetal age with a 95% confidence interval +/- 5 days.
Gestational sac may be 5 wks using the transvaginal probe.
A "double sac" sign or an "intradecidual" sign are not necessary findings with the new transvaginal probes. Any round or oval shaped fluid collection and a (+) preg test  likely intrauterine gestational sac.

5. First Trimester The Yolk Sac:
~ 3-5 mm Yolk sac starts appearing at 5&1/2 weeks . An embryo with a flickering heart beat starts appearing adjacent to the yolk sac at approximately 6 wks.
The yolk sac generally starts growing until the 10th week of GA, and then starts regressing. No identified consensus, but usually a 5-6 mm (inner diameter) is at the upper limit of normal. Larger inner diameter, abnormal contour/ecchogenic focus  may indicate a poor prognostic factor for the fetus.

6. Terminology and Diagnostic Tests Used Early in the First Trimester

7. Diagnosing Pregnancy Failure Using the Transvaginal Probe

8. Diagnostic and Management Guidelines Related to the Possibility of a Viable Intrauterine Pregnancy in Women with Pregnancy of Unknown Location

9. First Trimester
Normal Fetal Heart Rate: BPM. HR < 90 may be => poor prognostic factor.
Nuchal translucency (distance between the inner margins in the sagittal plane) (ref4) can be measured at weeks: Normal < 3 mm thickness. Increased thickness can be associated with aneuploidy/trisomy or cardiovascular abnormalities.
- Measured when the CRL is 39 – 84 mm
- A cystic Hygroma should be reported regardless of the size
(BIDMC MFM Guidelines)

10. SECOND AND THIRD TRIMESTERS

11. Second & Third Trimesters
Gestational age estimation is less reliable than the first trimester.
Estimating gestational age is based upon: Biparietal diameter, head circumference, femur diaphysis length and Abdominal circumference (Abdominal Circumference is less reliable than other parameters in assessing gestational age but helpful in assessing proportionality and growth of the fetus ).

12. Various Important 2nd/3rd Trimester Measurements
Cervical length (Mid Sagittal View): Normal > 3 cm .. Abnormal < 2.5 cm –3.0 cm is equivocal. .. Measure the shortest length seen during examination!!
Placenta: If the placenta does not extend into the cervix on the initial views  placenta previa is excluded!!
- Low Lying Placenta: The placenta approaches within 2 cm of the internal cervical os but it does not cover it.
- Marginal (Partial) Previa: The placenta extends into the edge but does not cover the internal cervical os .. {Some specialists prefer the use of descriptive terms suchas “The placenta is low-lying and ends just at the internal os” instead of Marginal/Partial Previa!!}
- Complete Previa: The placenta crosses over and covers the internal cervical os.
 FOLLOWUP: If Dx made at the 18 weeks examination; then follow up with repeat
ultrasound (in 10 weeks per Radiology)/(at 32 weeks gestational age per BIDMC
MFM)

13. Various Important 2nd/3rd Trimester Measurements
Lateral Ventricles (measured at the atria transversely): NORMAL </= 10 mm. Borderline ventriculomegaly is mm, and marked ventriculomegaly > 15 mm. (ref3) (BIDMC MFM Guidelines: > 10 mm  abnl)
Cisterna Magna (Posterior margin of the vermis to the inside of the occipital bone): abnormal > 10 mm (ref3) (This is also in accordance w/ BIDMC MFM Guidelines)
Nuchal Fold (measured at 15 wks -20 6/7 wks): NORMAL </= 6 mm. If increased  may reflect aneuploidy/trisomy 21. Later in pregnancy the nuchal skin becomes redundant and thicker and a 6 mm threshold does not hold. (ref4)
BIDMC MFM Guidelines
> 6 mm  ABNORMAL (Document in the report)

14. Various Important 2nd/3rd Trimester Measurements
Cerebellum (measured in the axial plane from the outer margins of its hemispheres): Not completely formed until weeks. It grows steadily as the head grows and measurements correlate with BPD and gestational age (ref4)
Consistent FHR > 160  ABNORMAL if persistent at >/= 24 weeks.
 Document and notify the Healthcare provider!!

15. Various Important 2nd/3rd Trimester Measurements
Renal Pelvis: (Transverse Plane & Calipers Ant Post) Controversial; some argue  4 mm up to 33 weeks and 7 mm afterwards till term, others state 5 mm to 20 weeks and then 10 mm.
- Normal:  < 5 mm after 20 weeks (< 4 mm at weeks)
- Equivocal:  5 - 9 mm (4 - 6 mm at weeks)
- Abnormal:  >/= to 10 mm (>/= to 7 mm at weeks)
(BIDMC MFM Guideline) :
< 20 weeks: >4mm is consistent with pyelectasis
>20 weeks: >5mm is consistent with pyelectasis
FOLLOW UP: In 10 weeks (per Radiology) or at 32 weeks (per MFM)
 >33 weeks: >7mm is consistent with hydronephrosis (requires neonatal f/u!!)

16. Various Important 2nd/3rd Trimester Measurements
Amniotic Fluid:
AFI >37 weeks
Oligohydramnios is an AFI <5cm
Polyhydramnios is an AFI >25cm
AFI <37 weeks
Oligohydramnios is an AFI <5m
Borderline low is an AFI 5-8cm
Polyhydramnios is an AFI >25cm

17. Various Important 2nd/3rd Trimester Measurements
Growth Parameters:
IUGR: EFW < 10th percentile for gestation age + < 2500 grams
LGA: EFW > 90th percentile
Macrosomia: EFW > 4000 grams

18. Various Important 2nd/3rd Trimester Measurements
ABNORMAL ECCHOGENIC FOCI
Echogenic Bowel: Bowel as echogenic as bone. ?? Cause; possibly due to swallowing of hemorrhagic products from the amniotic fluid, or due to loss of fluid from meconium. (Intra-amniotic hemorrhage, meconium ileus/CF, intra-uterine CMV, IUGR, trisomies, or in normal pregnancies)
Echogenic Focus in the Heart: “Echogenicity = BONE” ; MUST APPEAR ECHOGENIC in 2 PLANES. ??Mineralization in the cardiac papillary muscles. Isolated finding should be taken in the context of maternal risk as it can be seen in normal pregnancies, more common in the Asian population. However associated w/ higher risk of aneuploidy.
Pericardial Effusion: > 3 mm in diastole is ABNORMAL

19. Dating Error: When to Revise the EDD by U/S Parameters?
(BIDMC MFM Guidelines)
Up to 12 6/7 wks: > 7days
/7 wks: > 10 days
/7 wks: > 14 days
28 wks - term: > 21 days

20. References
Diagnostic Criteria for Nonviable Pregnancy Early in the First Trimester. Peter M. Doubilet, M.D., Ph.D., Carol B. Benson, M.D., Tom Bourne, M.B., B.S., Ph.D., and Michael Blaivas, M.D. for the Society of Radiologists in Ultrasound Multispecialty Panel on Early First Trimester Diagnosis of Miscarriage and Exclusion of a Viable Intrauterine Pregnancy N Engl J Med 2013; 369: October 10, 2013DOI: /NEJMra
Sonographic Evaluation of the Yolk Sac. Sinan Tan, MD⇓, Mine Kanat Pektaş, MD and Halil Arslan, MD. JUM January 1, 2012 vol. 31 no
Diagnostic Ultrasound. 3rd Edition. Rumack et al. Elsevier Mosby. St. Louis Missouri
The Requisites Ultrasound. W.D. Middleton, A.B. Kurtz, B.S. Hertzberg. Elsevier Mosby. Philadelphia, USA

21. Findings requiring Radiologist direct ultrasound evaluation and/or discussion with patient
EIF
Choroid plexus cysts
Nuchal fold abnormality
Abnormal nasal bone
Echogenic bowel
Situs abnormalities
2 vessel cord
Hydrocephalus
Radiology must review Major Abnormalites and discuss with patients
E.g.
Craniofacial
CDH
Cardiac outflow tract
Omphalocele/gut abnormalities
Renal agenesis/MCDK
Major MSK abnormalities
Does the radiologist need to review the following with the patient
Pyelectasis (do we automatically invoke standard follow up and the sonographer can let the patient know. Radiologist available for questions
Abnormal yolk sac
Bradycardia/tachycardia
Large cysterna magna
Gallstones
Renal ectopia
Which findings generate an automatic MFM referral
Radiologist should call provider for: