ANTECEDENT CIRCUMSTANCES SURROUNDING NEURAL-TUBE DEFECT BIRTHS IN 1990-1991

Objective To investigate births with neural tube defects at a time whe n most districts were screening for the condition. The objective was t o document the circumstances surrounding each affected birth and asses s the care provided against given standards. Design Retrospective revi ew of antenatal casenotes by the obstetric team. Population Three hund red and eight births in England and Wales in 1990 to 1991 were reporte d to the Office of Population Census Survey (OPCS) to involve neural t ube defects. Sufficient information was available to identify both the woman and the obstetrician in 213 pregnancies. Details were obtained from a questionnaire completed by the obstetric team for 168 (79%). In 20/168 cases either the reported outcome was not a live birth/stillbi rth or the pregnancy did not involve a neural tube defect: eight resul ted in a 'normal' infant, eight were terminated and in four the abnorm ality was not a neural tube defect. Thus 148 eligible cases were avail able for analysis. Results Of the 148 births, the anomaly was not dete cted prenatally or detected later than 25 weeks of gestation in 98 cas es (66%), diagnosed in a multiple pregnancy in 24 (16%) and diagnosed prenatally but the woman chose to continue the pregnancy in 26 (18%). Of the 98 births not detected prenatally or detected late during pregn ancy, the surrounding circumstances were that screening was declined i n six cases (4%), screening was not offered due to late booking in 30 (20%), serum alpha-fetoprotein screening gave a false negative result in eight (5%), ultrasound screening gave a false negative result in 29 (20%), both screening methods gave false negative results in 17 (11%) and other reasons in eight (5%). The estimated sensitivity of ultraso und screening for anencephaly was 100%. For spina bifida the estimated sensitivity for singleton pregnancies is higher for serum alpha-fetop rotein screening, 84% to 92%, than ultrasound screening, 70% to 84%, f or a range of assumptions regarding the degree of under-reporting to O PCS of live births and terminations. Conclusions Late booking preclude d the offer of screening tests in a substantial proportion (22%) of ca ses. The presence of multiple fetuses including one or more with a neu ral tube defect was a serious additional complication in prenatal scre ening, diagnosis and counselling. Screening for neural tube defects wa s widespread in 1990 to 1991, although variations in the services prov ided were documented. Ultrasound scanning was a major component but wa s associated with a lower sensitivity than maternal serum alpha-fetopr otein screening for neural tube defects other than anencephaly.