Impact of including elective pregnancy terminations before 20 weeks gestation on birth defect rates

The majority of U.S. birth defects surveillance programs do not include elective terminations before 20 weeks gestation among the pregnancy outcomes covered. To assess the impact of defects among elective terminations before 20 weeks gestation, data from a birth defects registry that does include terminations before 20 weeks gestation were analyzed.

Using information from the Texas Birth Defects Registry, the number of cases and rate of 49 conditions were analyzed in two ways: excluding defects detected among elective pregnancy terminations before 20 weeks gestation, and including defects among terminations before 20 weeks.

By including defects detected among elective terminations before 20 weeks, the number of cases increased by five percent or greater for nine conditions: anencephaly (29%); spina bifida without anencephaly (13%); encephalocele (21%); Patau syndrome (19%); Edwards syndrome (11%); Down syndrome (6%); omphalocele (15%); gastroschisis (5%); and anophthalmia (7%). There was no impact for 27 conditions, for which there were no cases detected among elective terminations before 20 weeks. The greatest impact was observed for anencephaly; the rate of anencephaly increased from 2.76 to 3.56 per 10,000 live births when defects among elective terminations before 20 weeks were included.

Excluding defects among elective terminations before 20 weeks results in counts and rates that are somewhat incomplete, especially for conditions that are more commonly detected and electively terminated before 20 weeks. The impact varies by condition.