Recommendations for indicators: night blindness during pregnancy--a simple tool to assess vitamin A deficiency in a population.

Night blindness during pregnancy caused by vitamin A deficiency is associated with an increased risk of morbidity and mortality among women. Because a history of maternal night blindness is simple and reliable to use, it is recommended as a population-based indicator of vitamin A deficiency. Furthermore, a maternal night blindness prevalence of >/=5% is recommended as a cut-off at which vitamin A deficiency may be considered to be a problem of public health significance within the community. This paper provides the justification for these recommendations. Night blindness during pregnancy is strongly associated with low serum and breast milk vitamin A concentration, abnormal conjunctival impression cytology and impaired dark adaptation, which suggests that it is a valid indicator of vitamin A deficiency. The prevalence of night blindness during pregnancy tends to be high in countries where the prevalence of xerophthalmia in children is high and in countries where interventions are in place to reduce childhood vitamin A deficiency. Existing data suggest that misclassification of self-reported maternal night blindness may account for a prevalence of up to 3%. The suggested cut-off, 5%, is set higher than this potential level of false-positive prevalence (3%). Illustrative data from India and Cambodia on childhood xerophthalmia and maternal night blindness rates are used to demonstrate the validity of using a 5% prevalence of maternal night blindness as indicative of a community vitamin A deficiency problem. Finally, it is recommended that night blindness history be elicited for a previous pregnancy that ended in a live birth in the past 3 y, using the local term for night blindness whenever possible.