Factors associated with congenital anomalies.

<p><b>A.</b> The incidence of congenital anomalies in males and females was calculated each year. Logistic regression analysis showed a significant downward trend in females (<i>p</i> < 0.0001, OR = 0.95, 95% CI 0.95–0.96), but not in males (<i>p</i> = 0.212, OR = 0.99, 95% CI 0.99–1.00). The difference in incidence between 1997 and 2011 was analyzed by the chi-square test in both genders, and a significant difference was observed in females (<i>p</i> < 0.0001) but not in males (<i>p</i> = 0.883). The difference in incidence between the genders in 1997 and 2011 was analyzed with the chi-square test, and a significant difference was observed in 1997 (<i>p</i> < 0.0001) and in 2011 (<i>p</i> = 0.001). <b>B.</b> The incidence of congenital anomalies at different maternal ages was calculated each year. Logistic regression analysis showed significant downward trends in all the age groups during the surveillance period (<i>p</i> < 0.0001). <b>C.</b> The incidence of congenital anomalies in the four different quarters was calculated each year. Significant reductions were seen in all seasons except the second quarter (<i>p</i> < 0.001), but no overall differences were seen between the seasons.