THE LIMITATION OF REFERRAL LEVEL FETAL ULTRASOUND EXAMINATION IN THE DETECTION OF SPINA-BIFIDA IN WESTERN-AUSTRALIA, 1990-1991

Objective: To ascertain babies born with spina bifida that was not det ected by prenatal ultrasound examination performed after 16 weeks' ges tational age at Western Australian referral centres, 1990-1991. Design : A retrospective study of the antenatal ultrasound details of those i nfants born with spina bifida in Western Australia during the 24-month period, 1990 and 1991. Data were collected by interviewing parents, c linically assessing affected individuals and reviewing genetic, clinic al and investigative records, and from the Birth Defects Registry of W estern Australia. Setting: Western Australia, which has a relatively h igh spina bifida birth prevalence of 1 in 1000, has centralised neonat al medical, surgical and genetic services, and a Birth Defects Registr y. This enabled us to ascertain all Western Australian neonates with s pina bifida for the purposes of this study. There is no universal mate rnal serum alpha-fetoprotein (MSAFP) screening program and the perform ance of ultrasonography at referral level is of variable quality. Part icipants: Newborns with spina bifida and their parents. Main outcome m easures: Ultrasound screening for spina bifida was deemed to have fail ed when referral to a specialist imaging centre for the specific purpo se of detecting anatomical abnormality after 16 weeks' gestational age gave a falsely negative result. Results: Of the 47 infants born with spina bifida in 1990 and 1991, ultrasound screening at more than 16 we eks' gestational age was documented and was falsely negative in 14. Si x of the 14 had a relevant family or medical history for the condition . Five of the lesions were covered and eight of the patients still sur vive. Conclusion: Ad-hoc fetal ultrasound examination via existing ref erral centres had obvious limitations in detecting spina bifida in a p opulation at low risk. MSAFP screening has a well documented role in d etecting neural tube defects, as eight to 1 0 of the 14 lesions missed by the referral ultrasonography would have been ascertained in a prog ram of this nature. The study indicated that adequate pre-screening cl inical histories were not sought, thus limiting the antenatal testing options offered to at-risk couples. This study emphasised the importan ce of a statewide review of the specificity and sensitivity of the ana tomical fetal ultrasound examination, in view of the expansion of this procedure and its variable quality depending on operator experience a nd equipment quality.