Objectives The number of new oral cleft patients has fallen in the Netherlands. This may be explained by two hypotheses: (1) greater prenatal detection of congenital anomalies has led to more pregnancy terminations and (2) increased folic acid use has reduced the oral cleft risk. Both hypotheses would mainly apply to the category cleft lip/alveolus ± cleft palate (CL±P), since, unlike cleft palate only (CP), CL±P can be detected prenatally by two-dimensional (2D) ultrasound and develops during the period recommended for folic acid use. The authors aimed to determine trends in prevalence over 1997–2006 and to evaluate the hypotheses by stratifying trends by cleft category.

Methods This study was a time–trend analysis of infants born alive with oral clefts in the Netherlands during 1997–2006 and registered in the national oral cleft registry. The authors calculated prevalence rates and the estimated annual percentage change (EAPC) for all oral clefts and the two categories.

Results In 1997–2006, 3308 infants out of 1 970 872 live births had oral clefts, an overall prevalence per 10 000 live births of 16.8 (CL±P: 11.3; CP: 5.5). Time–trend analysis showed that the prevalence of all oral clefts decreased (EAPC −1.8%; 95% CI: –3.0% to −0.6%), as did the CL±P prevalence (EAPC −2.3%; 95% CI: −3.8% to −0.9%). No significant trends were found for the CP prevalence.

Conclusions Because the live-birth prevalence of CL±P decreased, that of all oral clefts decreased. These findings are in line with both hypotheses and may therefore have implications for prenatal counselling and folic acid policy.