Published trends and geographical differences in
cryptorchidism rates are almost exclusively
derived from hospital-based
birth defect registers, which are sensitive to
selection bias and incomplete reporting. This study aimed to accurately assess the
cryptorchidism prevalence in the general population of Rotterdam. Of 7652 consecutive male
live births, 7292 (95%) were examined for
cryptorchidism at Child Healthcare Centres around the age of 1 month. In a subgroup of cases, the persistence of
cryptorchidism was re-assessed during a follow-up examination by expert specialists. The
cryptorchidism rate at the
median age of 35 days was 1.2% (89/7292). In the re-examined subgroup (
median age 95 days) 69% of the boys (24/35) had persistent
cryptorchidism, of which 20 were unilateral and four bilateral. The population rate of 1.2% falls within the range of 0.9-9% reported by others. Differences in case ascertainment and population characteristics probably explain part of the differences between studies. Our
cross-sectional design does not allow for analysis of a
temporal trend, but provides a baseline for future trend studies. To study
cryptorchidism rates, trends, and
risk factors, a systematic case ascertainment is warranted.
