The Epidemiology of Neural Tube Defects in Newfoundland and Labrador

Abstract

Objectives: To describe the epidemiology of neural tube defects (NTDs) in Newfoundland and Labrador, including geographic, seasonal and secular variation, and associated anomalies.Methods: All cases of NTDs between 1992 and 1998 identified in the Newfoundland and Labrador Neural Tube Defect Database were included. Information evaluated from each case included the date of the last menstrual period, mother’s place of residence, sex of the fetus or child, and occurrence and type of additional anomalies. Rates by geographic region were based on total birth rates for the community health regions of the province. Rates by season of conception were based on the last menstrual period and the total birth rates nine months later. Statistical analysis was with parametric and nonparametric tests, where appropriate.Results: Information in the database allowed identification of 165 NTDs in newborns, for a rate of 3.92 NTDs per 1000 births. St. John’s had a significantly higher rate of NTDs (4.86/1000) compared to the rest of the province (3.53/1000; p = 0.044) or to the adjoining region of Eastern Newfoundland (3.03/1000; p = 0.029). Grenfell (Northern Newfoundland) had a significantly higher rate (5.79/1000) compared with the adjoining region of Labrador (1.90/1000; p = 0.041). Twenty percent of fetuses had at least one extra central nervous system anomaly, including omphalocele, diaphragmatic hernia, renal, cardiac, anal atresia, cleft lip/palate, and musculoskeletal, with five having multiple extra central nervous system anomalies. A higher rate of NTDs was found in spring (5.02/1000) and summer (4.33/1000) combined than in autumn (2.96/1000) and winter (3.16/1000; p = 0.008). Secular trends found a reduction in the incidence of NTDs in 1997 and 1998 compared to earlier years (p < 0.0001).Conclusion: The incidence of NTDs in Newfoundland varies by season and by geography. The geographic variation may be partly explained by the ethnic backgrounds of the different regions of the province, as well as by the varying availability of foods rich in folate. The reduction in the incidence of NTDs in the last two years of the study may represent normal fluctuations in incidence, or perhaps more significantly a reduction due to increased awareness and use of periconceptual folic acid, as well as the introduction of fortification of flour with folate.