Sonographic values in obstetrics and gynaecology

Obstetric and gynaecological ultrasound is rampant with numerous cut off values. Some of these get revised over the years. The following list is a useful aid to refer to and revise.

  • 1 mm
  • 2 mm
  • 2.5 mm
    • considered by some as the upper limit for a normal nuchal translucency (others take it as 3 mm)
    • traditional single cut off lower limit value for a nasal bone length below which it is considered as a hypoplastic nasal bone
  • 3 mm
    • considered by some as the upper limit for a normal nuchal translucency (others take is as 2.5mm)
    • considered by many as the upper limit of seperation between the choroid and the medial wall of the ventricles in or to support the diagnosis of a mild fetal ventriculomegaly
  • 4 mm
    • considered by some as the lower limit for an endometrial thickness below which is interpreted as endometrial atrophy
    • considered by many as the upper limit for a fetal renal pelvic diameter in the second trimester beyond which it is taken as fetal renal pelvic dilatation
  • 5 mm
    • depth of invasive component for cervical cancer to be upgraded from stage Ia to stage Ib
    • accepted upper limit for an endometrial thickness in a post menopausal patient
    • considered by many as the upper of the thickness of fetal subcutanous tissues beyond which it is interpreted as fetal anasarca
    • upper size limit of microcysts in a type III CPAM
    • accepted upper limit for an endometrial thickness following a DC/STOP procedure beyond which the diagnosis of retained products of conception should be considered 
    • considered by some as a mininum size difference between a gestational sac over the size of the fetal pole for a healthy pregnancy
  • 6 mm 
  • 7 mm
    • recently revised RCOG recommendation for CRL beyond which a fetal heart beat should be seen (ASUM criteria in process of revision).
    • width of invasive component for cervical cancer to be upgraded from stage Ia to stage Ib 
  • 8 mm
    • maximal gestational sac diameter (MSD) on a transvaginal scan beyond which a yolk sac should be seen for a viable pregnancy
  • 10 mm: 1 cm
    • upper limit for the accepted width of normal fetal ventricles beyond which it is considered as mild fetal ventriculomegaly
    • considered by some as a upper limit for a simple appearing anechoic ovarian cyst beyond which sonographic follow up required in a post menopausal patient
    • upper limit for the diameter of the cisterna magna beyond which it is considered as a mega cisterna magna
  • 12 mm: 1.2 cm
  • 15 mm: 1.5 cm
  • 16 mm: 1.6 cm
    • considered by some as the upper limit of normal for gestational sac diameter (MSD) on a transvaginal scan scan beyond which a fetal pole should be seen for viable pregnancy: some consider this as 20 mm
  • 20 mm: 2 cm
    • considered by some as the upper limit of normal for gestational sac diameter (MSD) on a transvaginal scan scan beyond which a fetal pole should be seen for viable pregnancy (current ASUM criteria)
    • considered by some as the upper limit of size for a gestational sac (MSD) on a transabdominal scan beyond which a yolk sac should be visible 
    • minimum depth of amniotic fluid pocket below which it is reported as oligohydramnios
    • accepted by many as the minimum distance between the placental edge and the internal cervical os below which it is classified as a low lying placenta
    • size of peritoneal deposits in ovarian cancer which differentiates stage IIIb from stage IIIc
  • 25 mm: 2.5 cm
    • upper limit for mean sac diameter on a trans-abdominal scan beyond which a yolk sac should be seen for viable pregnancy
    • recently revised RCOG recommendation for upper limit MSD beyond which a fetal pole should be seen (ASUM criteria in process of revision).
    • accepted lower limit for a cervical length up to ~24 weeks below cervical incompetence is considered
  • 30 mm:  3 cm
    • considered by many as the upper limit for a ovarian cyst or paraovarian cyst in a premenopausal patient beyond which it should be mentioned on a radiology report
  • 35 mm: 3.5 cm
    • considered by some as the lower limit length of the umbilical cord to be considered as a short umbilical cord
  • 40 mm: 4 cm
  • 45 mm: 4.5 cm
  • 50 mm: 5 cm
    • considered by some as the upper limit for a ovarian cyst or paraovarian cyst in a premenopausal patient beyond which sonographic follow is recommended 
  • 70 mm: 7 cm
    • considered by many as upper limit for a simple appearing ovarian cyst or paraovarian cyst beyond which MRI is recommended for full evaluation
    • considered by many as upper limit for the umbilical cord length beyond which it is taken as a long umbilical cord
  • 80 mm:  8 cm 
    • maximum depth of amniotic fluid pocket below which it is reported as polyhydramnios
  • 84 mm: 8.4 cm

See also

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Article information

rID: 15582
Section: Gamuts
Tag: refs
Synonyms or Alternate Spellings:
  • Measurement values in obstetrics and gynaecology
  • O & G measurement values
  • Ultrasound values in obstetrics and gynaecology
  • Sonographic values in obstretrics and gynecology

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