Objectives: To determine the prevalence of pregnancies with a neural tube defect (NTD) in England and Wales between 1964 and 2004 and to estimate the relative impact of antenatal screening and a change in the incidence of these defects on the prevalence of births with NTDs.
Settings: Use of data published by the Office for National Statistics (ONS) on terminations of pregnancies with an NTD and births with an NTD from 1964 to 2004.
Methods: Estimates were made of the total number of terminations of pregnancies and births with an NTD by taking account of the under-reporting of these terminations and births using a previously described method. In 1995 ONS started to report the number of terminations with an NTD rather than the total numbers of terminations with a central nervous system (CNS) malformation that had previously been used to estimate the number of NTD terminations. Adjustment was made for this and new estimates of the total number of NTD pregnancies were produced to 2004.
Results: There were an estimated 969 pregnancies with NTDs (168 (17%) births and 801(83%) terminations) in England and Wales in 2004. An estimated 44% of NTD terminations and 32% of births were not reported as such. The birth prevalence per 1000 decreased fallen 93% from 3.6 in 1964 to 0.3 in 2004, 59% due to an underlying decrease in the prevalence of NTDs and 34% due to screening diagnosis and subsequent termination of affected pregnancies.
Conclusion: The prevalence of NTD pregnancies decreased by around two per 1000 from 1964 to 1990 and thereafter remained fairly constant. The prevalence of NTD pregnancies is substantially underestimated if it is based only on reported NTD births (by 88%) and also if it is based on reported NTD births and terminations (by 52%), because most NTD pregnancies in England and Wales are terminated following antenatal screening and most of these terminations are not reported.
