Screening Ultrasound

Screening Ultrasound Defined
  • Sonographic assessment of the pregnant abdomen between 16 and 20 weeks EGA (second trimester), in the absence of specific indications for a second-trimester ultrasound.
Screening Ultrasound
The basic sonographic examination should provide the following information:
  • Fetal number
  • Fetal presentation
  • Documentation of fetal life
  • Placental location
  • Fetal biometry
  • Assessment of amniotic fluid volume
  • Assessment of gestational age
  • Survey of fetal anatomy for gross malformations
  • Evaluation for maternal pelvic masses
Ultrasound in Pregnancy Summary – ACOG February 2009
  • US examination is an accurate method of determining GA, fetal number, viability, and placental location (Level A).
  • Ability to diagnose major fetal anomalies established (Level A)
  • Specific indications are the best basis for use in pregnancy.
    – Optimal timing in the absence of specific indications is at 18-20 weeks.


Limited Bedside Transvaginal Ultrasound in ED

Correlation of Gestational Age, b-HCG level, and TVUS findings

 Gestational age  B-HCG (mIU/ml)  TVUS findings
 4.5-5 weeks  <1,000  Gestational sac
 5 weeks  1,000-2,000  Gestational sac + DDS*
 5-6 weeks  >2,000  Yolk sac** (+/- fetal pole)
 6 weeks  10,000-20,000  Embryo with cardiac activity
 7 weeks  >20,000  Embryonic torso/head



**DDS = double *DDS = double decidual sign
**First definitive evidence of IUP


  • B-HCG of 1,500 is considered the discriminatory zone, i.e. minimum quantitative level of HCG at which intrauterine pregnancy should be seen by ultrasound. 
  • Abnormal gestation or embryonic demise if:
    • Gestational sac > 10 mm without a yolk sac
    • Gestational sac > 18 mm without a fetal pole
    • Fetal pole > 5 mm without cardiac activity
  • If the B-HCG is > 1500 and no GS is seen
    • Ectopic pregnancy
    • Completed abortion
  • If the B-HCG is < 1500 and the uterus is empty
    • Early normal pregnancy
    • Ectopic pregnancy
    • Completed abortion
  • Serial B-HCG value in 48 hours
    • Live IUP: doubles
    • Completed abortion: decreases
    • Ectopic pregnancy: stable or small rise



Determine Gestational Age by Ultrasound
7-14 weeks Crown-rump length  (distance from the top of the head to the bottom of the fetal spine)
Second trimester Biparietal diameter and femur length are used
Third trimester biparietal diameter, abdominal circumference, and femur length are best for estimating gestational age

According to ACOG, which of the following statements best characterizes the use of sonography in pregnancy?

A. It has the ability to diagnose minor fetal anomalies.
B. It is best carried out at 12 weeks estimated gestational age.
C. It is an accurate method of determining placental location.
D. Routine use is recommended.