Incidence of congenital pyloric stenosis in birth series.

CONFEN~TAL hypertrophic pyloric stenosis has been linked with primogeniture in many reports since Still [l] first suggested that its incidence might be associated with birth rank. Principal contributors to this view are: Ford, Ross and Brown [2]; Cockayne and Penrose [3]; McKeown, MacMahon and Record [4, 51. Most recently this view has been advanced by Shim, Campbell and Wright [6]. These authors have used various methods in reaching this conclusion. Ford, Ross and Brown [2] assembled a large group of pyloric stenosis cases and compared the percent distribution of birth ranks within the general population as presented by census data for the city of Toronto and the province of Ontario, Canada. Cockayne and Penrose [3] followed the method of Greenwood and Yule, in the Journal of Royal Statistical Society, January 1914, to generate an expected proportion of cases at each birth rank for their study population, to which they compared their actual proportion of cases found. McKeown, MacMahon and Record [4] used a control group of randomly selected live births in the same years in the same city to compare proportionate distributions of birth ranks among afflicted and unafflicted groups. Shim, Campbell and Wright [6] compared the birth order distribution of their case material to Hawaii population data. A few investigators have dissented from the conclusion that pyloric stenosis is related to primogeniture. Delprat and Pflueger [7] have commented that comparisons are questionable because of inadequate information about the proportion of firstborn among all living children. Benson and Warden [8], using a group of 707 cases, found the proportion of firstborn did not differ from the general United States population, estimating the number of firstborn from average family size. Most data used to investigate the question have been derived from clinic sources, which include information about the sibships only at times of patient treatment or follow-up. This means that most families had incomplete sibships at the times information was collected. In previous work the authors have shown that efforts to relate birth order to incidence of congenital pathology reach inaccurate conclusions when based on information which is temporally limited to an incomplete accounting of the full series