Background and aims Critical congenital heart diseases (CCHD) can be missed by prenatal ultrasound and physical examination (30%newborns unrecognised CCHD). This fact entails risk of cardiogenic shock, neurological damage and death. The American Paediatric Association supports the universal screening of CCHD by pulseoximetry.

This study aimed to evaluate the rate of unrecognised CCHD in newborn before the universal pulseoximetry was stablished in Spanish third level hospital. To describe the initial results after its implantation.

Methods 1) Retrospective review, showing the incidence of CCHD and late detection rate before pulseoximetry screening implantation. 2) Prospective analyse, after its recent introduction.

Were assessed pulseoximetry preductal and postductal before hospital discharge. Screen was considered abnormal: 1) Oxygen saturation <90%, 2) Oxygen saturation <95% in both extremities on 3 measures,(3) >3% difference oxigen saturation between right hand and foot.

Results Incidence CCHD in 18 months before pulseoximetry was 1,8:1000. There were 10 CCHD diagnosed out of 5500 newborn: 3(30%) prenatally, 4(40%) by physical examination before discharge and 3(30%) after hospital discharge. Since pulseoximetry screening (May 2013), there have been 4 patients (out of 3068 deliveries) with CCHD, all of them diagnosed before hospital discharge (2 prenatally, 2 by physical examination and pulseoximetry). There were 2 false positives (0,06%), one of them was diagnosed of situs inversus totalis, probably related to Kartagener syndrome.

Conclusion Conventional screening for congenital heart disease can lead to a significant rate of unrecognised CCHD. Pulseoximetry may be a useful screening test, false-positive rate was particularly low (<0,1%).

More studies are needed to assess its long-term real value and economic impact in our heath system.