birth defects, APORS is able to both study disease patterns and refer infants to local health departments and other providers for follow-up services. Although they can occur at any stage of pregnancy, most birth defects occur during the first trimester when a baby’s organs are developing. While the causes of some birth defects are known, there is still a lot to learn. Most defects are likely caused by a complex combination of genetic, human behavioral, and environmental factors (Centers for Disease Control and Prevention, 2021, March 2 ) and research is ongoing to assess how these factors interact to cause birth defects. Research to date indicates that some factors (alcohol, tobacco, or drug use) or maternal conditions (obesity, diabetes, older maternal age, genetic patterns) present during pregnancy may increase the chance of a birth defect. However, it is also important to note that birth defects can occur when none of these conditions or exposures are present. Consulting with a physician and preparing to be as healthy as possible, both before and during pregnancy, may increase the likelihood of having a healthy baby. APORS is the most complete source of data on birth defects in Illinois. At its inception, APORS relied primarily on reports sent from hospitals to identify cases, but the program has evolved over time and currently uses multiple sources of data and active surveillance methods to identify and verify cases. All Illinois hospitals are mandated to report infants with adverse pregnancy outcomes born to women who are Illinois residents. (Perinatal centers in St. Louis also participate.) Birth, death, and fetal death certificates (maintained by the IDPH’s Division of Vital Records) are an additional data source, allowing APORS to identify infants with certain birth defects or other conditions unreported by the hospitals. The IDPH Division of Patient Safety and Quality, which collects patient level discharge data from Illinois acute care hospitals, provides 2 information about children under the age of 2 with a documented birth defect. This allows APORS to identify children whose birth defect diagnosis was made after their newborn stay, or who were unidentified for other reasons. Importantly, APORS undertakes systematic active case verification of cases reported to APORS and those identified through other sources. APORS staff members review charts for infants reported with selected serious birth defects. As the charts are reviewed, APORS staff correct and add to information reported by hospitals. An abstractor liaison oversees these activities to ensure the most accurate and complete information is recorded. Table 1 below describes the activities APORS has undertaken over the yearsto expand case and birth defect finding since 2002. Table 1: Projects to Identify Cases and Birth Defects Birth years Activity Implemented Purpose 2002 onwards Active Case Verification Identify unreported or misreported diagnoses through review of infant charts using criteria listed in Table 2. 2012 onwards Abstractor Liaison Oversight Oversee case abstraction accuracy and completeness. 2013 onwards Electronic Case Reporting Systematic prompting of hospitals to report birth defects when documented on the birth certificate. 2013 onwards Hospital Discharge Case Finding Identify birth defects noted in review of hospital discharge data, but not reported to APORS. 2015, 2016 Rapid Case Identification Identify conditions potentially related to the Zika virus, including brain and eye anomalies, neural tube defects, and arthrogryposis. Since systematic active case verification began in 2002, there have been modifications to the criteria that establish which charts are reviewed. Details are given in Table 2. 3 Table 2: Criteria that Determine Which Charts are Reviewed Birth years Chart Review Criteria 2002 -2007 ۰ one or more birth defects, ۰ very low birth weight (< 1500 g), ۰ exposure to alcohol, ۰ a diabetic mother, ۰ a disturbance in neonatal tooth eruption, or ۰ death before discharge. 2008-2012 ۰ selected birth defects including those covered in this report, ۰ exposure to alcohol. ۰ a diabetic mother. ۰ a disturbance in neonatal tooth eruption, or ۰ death before discharge. 2013 onwards ۰ selected birth defects including those covered in this report, ۰ exposure to alcohol, ۰ a disturbance in neonatal tooth eruption. Each of these conditions has a high likelihood of being associated with one or more birth defects. As a result, the use of active case verification allows APORS to identify and verify more birth defects each year when compared to past years when this methodology was not used. This increase in the number of verified diagnoses is the combined result of a number of factors: i. The APORS chart review takes place several months after discharge, and additional diagnoses have been made since the children were reported to APORS. ii. The diagnostic test results are placed in the chart after discharge and are not seen by the reporting hospital staff. iii. Hospital reporting staffs are likely to report one or two major birth defects for each child and may not include associated, but less significant birth defects. However, at times defects may be reported that do not meet APORS’ criteria because: i. a clinical diagnosis was suggested and reported, which was later ruled out by a diagnostic test; ii. some defects are only collected in special