Volume 8 Issue 3 - Australasian Society for Ultrasound in Medicine

POLICIES and STATEMENTSFetal structureThe following list of gestational agesat which various fetal structures maybe visualised is not intended to providea complete list of what shouldbe examined. However, using highresolution equipment (often only witha vaginal transducer) the followingstructures can commonly be seen:9 weeks Head, trunk and limbs10 weeks Some ossification oflong bones, jaw and skull11 weeks Stomach, spine, ossifiedcranium, four chamber heart12 weeks Mid gut herniation nolonger present, kidneys, bladder.Nuchal translucencyThe nuchal translucency measurementis a test to assess the risk of chromosomalabnormality, in particular of trisomy21. The measurement may alsobe abnormal in other fetal anomalies(e.g. some congenital heart disease). Ithas been estimated that first trimesterscreening by a combination of sonographyand material serum testing ofPAPP-A and free βhCG can potentiallyidentify 94% of trisomy 21 fetuseswith a false positive rate of 5% 2 .This study should be performedby adequately trained staff accordingto strict protocol. The outcomesof the test should be audited regularly.The recommendations of theFetal Medicine Foundation/ RoyalAustralian and New Zealand Collegeof Obstetricians and Gynaecologistsshould be noted.It may be performed between thegestational ages of eleven (11) weeksand thirteen (13) weeks plus six (6)days (CRL 45–84 mm). A measurementgreater than 2.5–3 mm is usuallyconsidered to be abnormal but mustbe correlated with gestational age.Reference values have been providedby Nicolaides 3 .The nuchal translucency measurementmay be performed at the requestof the referring Medical Practitioner.Due consideration should be given asto how and who is going to counselthe patient prior to the performance ofa nuchal translucency scan.Each practice should develop awritten protocol on the procedure tobe followed when the measurementis abnormal. This protocol shouldinclude guidelines for the immediatecare of the patient and how the referringdoctor will be informed. Usuallythe referring doctor should be notifiedso that appropriate counseling may begiven and the patient can be referredto a specialised unit where formal riskassessment and counseling processcan be undertaken.Method of measurement1 The nuchal translucency shouldbe measured on a sagittal midlinescan through the fetus.2 The fetus should be in neutral positionand occupy at least 75% of theimage.3 The amnion should be seen separateto the fetal skin line.4 Calipers should be positioned tomeasure the maximum diameter ofthe fluid at the back of the neck.Ovaries, uterus and adnexaEach ovary should be examined.The corpus luteum can vary greatlyin appearance during the first (andearly second) trimesters of pregnancy.Sonographic appearances includea solid, rounded target like lesionor a predominately cystic structure.Peripheral vascularity is usuallydetectable.The size of a corpus luteum is alsovariable, commonly measuring up to3 cm.Larger or unusual masses shouldassessed as in the non pregnantwoman.The uterus should be examined forevidence of a fibroids or uterine developmentaldefects. The uterine positionshould also be noted (anteverted,axial, retroverted).The adnexa should be examinedfor coexistent ectopics and free fluid.References1 Hately, Case and Campbell. Establishingthe death of an embryo by ultrasound.Ultrasound Obstet. Gynecol 1995; 5:353–357.2 Nicolaides KH Am J Obstet Gynecol 2004;191: 45–47.3 From Nicolaides group: Snijders et al..Assessmant of risk of Trisomy 21 bymaternal age and fetal nuchal-translucencythickness.34 ASUM Ultrasound Bulletin 2005 August; 8 (3)