Cardiovascular malformations: changes in prevalence and birth status, 1972-1990

Through an ongoing hospital-based active malformation surveillance program, we identified cardiovascular malformations (CVMs) in 3.3 per 1,000 liveborn and stillborn infants, and fetuses from pregnancies terminated electively during a 15-year period. We excluded the children of mothers who had planned delivery elsewhere, but were transferred for care of anomalies that had been detected in prenatal screening. Birth status changed markedly during the study with a significant increase in elective terminations of fetuses with a CVM from 0 to 22% (P < 0.01 based on a test for trend). The proportion of liveborn infants with CVMs decreased from 90% to 73% (P < 0.01); the frequency of stillbirths did not change. During the study period, there was a significant increase in the prevalence of CVMs in all births (P < 0.01) and elective terminations (P < 0.01). The increase in liveborn prevalence was not statistically significant (P = 0.08). Stillborn prevalence was unchanged. The number of mothers having prenatal ultrasonography (P < 0.01 for trend) and amniocentesis (P < 0.01 for trend) increased steadily. There were significant increases in the proportion of mothers having any ultrasound examination (P < 0.01 for trend), the number of initial ultrasound examinations occurring in the second trimester (P < 0.01 for trend), and the proportion of mothers having amniocentesis (P < 0.01 for trend). There was a significant increasing trend in the proportion of mothers who were 35 years and older (10% in 1972-1974, 26% in 1988-1990, P < 0.01). This hospital-based active surveillance program suggests that more frequent elective terminations had a significant effect on overall birth prevalence of CVMs. This trend would not have been detected by most other surveillance systems which determine prevalence of common birth defects from birth certificates and other forms of administrative reporting, and exclude elective terminations of pregnancy.