Introduction Babies with cardiac anomalies are often asymptomatic at birth, and many remain undetected despite routine newborn examination. We retrospectively assessed the effect of routine pulse oximetry in detection of such anomalies from a hospital birth population of 31 946 babies born between 1 April 1999 and 31 March 2009.

Method 29 925 babies who were not admitted to the neonatal unit at birth underwent postductal oxygen saturation measurement before discharge. If saturation was below 95% an examination was performed. If this was abnormal or saturation remained low, an echocardiogram was performed. All babies with cardiac anomaly diagnosed before 1-year were identified from the region's fetal abnormality database.

Results Critical anomalies affected 27 infants (1 in 1180); 10 identified prenatally, 2 after echocardiogram was performed because of other anomalies, 2 in preterm infants, 2 when symptomatic before screening, 5 by oximetry screening, 1 when symptomatic in hospital after a normal screen and 5 after discharge home.

Serious anomalies affected 50 infants (1 in 640); 8 identified antenatally, 7 because of other anomalies, 3 in the neonatal unit, 5 by pulse oximetry screening, 11 by routine newborn examination, and 16 after discharge home.

Conclusions Routine pulse oximetry aided detection of 5/27 of critical and 5/50 of serious anomalies in this sample, but did not prevent five babies with critical and 15 with serious anomalies being discharged undiagnosed. Results from screening over 250 000 babies have now been published, but this total includes only 49 babies with transposition, and even smaller numbers of rarer anomalies.