THE EPIDEMIOLOGY OF DIAPHRAGMATIC-HERNIA

We studied the epidemiology of diaphragmatic hernia based on 1439 case s collected from a French, a Swedish, and a California birth defect re gistry. This is the largest epidemiological material available up to n ow. Isolated diaphragmatic hernia existed in 875 infants, diaphragmati c hernia with associated malformations in 486, and with chromosome ano malies in 78. Among unilateral forms, right-sided hernias were found i n about 20%, equally often in isolated and associated forms. There is a male excess of the same magnitude in isolated and associated forms b ut among the latter varying between programs. There was a change in th e sex distribution of associated cases in California before 1988 and a fter which is not fully explained. The twinning rate is increased and is similar in isolated and associated forms. There is no marked effect of maternal age or parity on the risk of diaphragmatic hernia. Except for well-known conditions, no specific combination of associated malf ormations was found. Marked differences in recorded rates were found b etween the programs but not between races within the California progra m. The differences appear to a large extent to be due to different asc ertainment, also apparent in different survival rates. Marked variatio ns in rate with time is seen in the two programs with an extended obse rvation time, again at least partly explainable by varying ascertainme nt.