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
rate of increase of a mean sac diameter per day in early pregnancy
2 mm
generally accepted value for a thickness for a significant fetal pericardial effusion
generally accepted thickness for a decidual reaction for an early pregnancy
generally accepted thickness of an intertwin membrane in order differentiate a MCDA from a DCDA pregnancy
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
considered by many as the upper limit for a nuchal thickness
maximal CRL beyond which a fetal heart rate should be seen for a viable pregnancy under current ASUM criteria
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
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
accepted by many as the upper limit for a junctional zone in MRI above which is concerning for adenomyosis
15 mm: 1.5 cm
upper limit for the accepted width of normal fetal ventricles in mild fetal ventriculomegaly beyond which it is considered as fetal hydrocephalus
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
considered by many as the maximal placental thickness at any gestation beyond which is it taken as placentomegaly
45 mm: 4.5 cm
often accepted as the lower limit for a CRL in order for a nuchal translucency to be valid
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
often accepted as the upper limit for a CRL in order for a nuchal translucency to be valid