Introduction: The study aimed to prove or disprove a clinical suspicion of a decreasing frequency of pyloric stenosis.
Method: Retrospective review of hospital records of all children operated for pyloric stenosis in the hospitals of the County of Viborg from 1 January 1973 to 31 December 1997. This regional review was supplemented by a nationwide study, in which the National Registry of Patients was searched for the diagnosis number and the operation code of pyloric stenosis during the period 1 January 1977 to 31 December 1997.
Results: One hundred and forty-seven children were operated for infantile hypertrophic pyloric stenosis in Viborg County during the period in question. When calculated in five-year periods, the respective numbers per 1000 liveborn children were: 1.6, 2.4, 2.0, 2.8, and 0.9. Only one child was operated per year during 1996 and 1997, compared with an average of seven children annually during the preceding 20 years. The same tendency was found in the nationwide study. Until 1993 an average of 160 children were operated per year, i.e. 2.2 to 3.2 per 1000 liveborn children. From 1993-1997 inclusive the number decreased to 1.4. In 1996 and 1997, respectively, 75 and 76 children were operated, i.e. 1.1 per 1000 liveborn children.
Conclusion: There has been a significant decrease in the incidence of children with infantile hypertrophic pyloric stenosis, both in the County of Viborg and in the whole of Denmark. The decrease, which started in 1993, has for unknown reasons continued to accelerate ever since. The decrease coincides with changing recommendations concerning the positioning of infants during sleep, but a causal connection is uncertain.