the 2013 to 2018 period. Since the latter time period is shorter and reflects a time of changes in data collection methodologies, the results may be less reliable. One defect (hypospadias) showed a significant trend during both time periods. Table 3 includes columns with average annual percentage change that gives an estimate of how quickly the rate changed over time for each time period. For example, the rate of anotia/microtia was increasing by an average of 8.3% each year during 2002 and 2012 and 3.3% each year between 2013 and 2018. The change over the second time period was not statistically significant, however. Figures 1 to 9 show the rates over time for birth defects during the two time periods of 2002-2012 and 2013-2018. Rates for Down syndrome are also plotted by maternal age group in Figure 10. Regression lines are plotted for each birth defect and time period. The regression lines are usually log-linear but may be made up of several straight line segments with different slopes. Although examination of the graphs may show some birth defects with a marked slope, the small number of cases means that the slope is not statistically significantly different from horizontal (no change with time). Several defects may show trending in differing directions for the two time periods. This may be caused by several factors including instability of the estimates of trend for the latter period due to the small number of time points between 2013 and 2018, or changes in data collection methods during that period. Some estimates may have been affected by the change from the ICD-9 to ICD10 coding scheme used by hospitals and officially enacted in October 2015 (Salemi et al., 2019). Finally, it is also possible the trends are sound and will remain as additional years are examined in future trend studies. Illinois data do not include birth defects that are diagnosed prenatally where the fetuses are subsequently terminated. This means that the Illinois observed incidence rates for conditions where terminations occur are lower than they should be. When examining trends, this will not affect the trend, provided the termination rate does not vary over time. 7 Table 3. Birth Defects Showing a Significant Trend in Incidence Rate Between 2002 and 2012 or Between 2013 and 2018 Selected Birth Defect Significance of trend (P-value) Average annual % change between 2002 and 2012 Significance of trend (P-value) Average annual % change between 2013 and 2018 Anotia/Microtia 0.00 8.3 not significant 3.3 Ventricular septal defect 0.02 2.8 not significant 5.2 Endocardial cushion defect 0.00 3.7 not significant -0.3 Tricuspid valve atresia, stenosis and other anomalies 0.00 5.8 not significant -23.3 Coarctation of aorta not significant 1.9 0.00 9.3 Aortic valve stenosis not significant 2.2 0.00 22.2 Hypoplastic left heart syndrome not significant -0.1 0.00 17.3 Rectal and large intestinal atresia/stenosis 0.00 -1.8 not significant 2.2 Renal agenesis/hypoplasia 0.00 7.0 not significant 8.2 Hypospadias 0.00 2.7 0.00 6.9 Source: Illinois Department of Public Health, Adverse Pregnancy Outcomes Reporting System, March 2021 Discussion of Illinois Results The rate of anotia/microtia increased significantly from 2002 to 2012. Between 2013 and 2018 the rate increased as well but was not significant. The CDC reports that for most babies, the causes of anotia/microtia are not known. However, use of the medication isotretinoin(Accutane®) during pregnancy has been identified as one cause, and genetic mutations or complex genetic environmental factors may also elicit these defects. Women with (pre-existing) diabetes and women who consume a low carbohydrate diet during pregnancy may also be at an increased risk of having a baby with anotia/microtia (CDC, 2021, March 25). A recent study covering 30 birth defects surveillance systems in the United States, including Illinois, found the highest prevalence rates of anotia/microtia among infants born to Hispanic 8 women when compared to other racial/ethnic groups. Prevalence rates were also found to be higher among infants born to non-Hispanic Asian Indian/Alaska Native and non-Hispanic Asian/Pacific Islander women when compared to non-Hispanic Black and White women (Stallings et al., 2018). The same study also noted a higher prevalence of these defects among infants of women ages 40 and older when compared with other age groups. In Illinois, while the proportion of births to Hispanic women has decreased slightly during the study period (2002-2018), the proportion of births to non-Hispanic Asian/Pacific Islander women increased from 4.6% in 2002 to 6.7% in 2018. Also, the proportion of births to women 40 or more years of age has increased from 2.4% in 2002 to 3.5% in 2018. The increases in these populations may partly explain the rising rates of anotia/microtia in Illinois. The change from ICD-9 to ICD-10 coding may also explain rising rates after 2015 (Salemi et al., 2019). Significant increases were seen in three cardiovascular defects from 2002 to 2012, including ventricular septal defect, endocardial cushion defect, tricuspid atresia/stenosis, and other anomalies. During the period of 2013 to 2018, significant increases were noted for an additional three defects, including coarctation of aorta, aortic valve stenosis, and hypoplastic left heart syndrome. Heart defects are the most common type of birth