The concept of using pulse oximetry (PO) as a screening test to identify newborn babies with critical congenital heart defects (CCHD) before life-threatening collapse occurs has been debated for some time now. Several recent large studies have consistently shown that PO screening adds value to existing screening techniques with over 90% of CCHDs detected. It can also help identify newborn babies with low oxygen saturations due to infection, respiratory disease and non-critical CCHD. Many countries have now introduced PO screening as routine practice, and as screening gains more widespread acceptance in the UK, we have focused more on the practical aspects of screening in this article. This includes case reports to demonstrate how the different screening modalities for CCHD work together and the experience of hospitals that have already introduced PO screening programmes (Birmingham Women's Hospital and others). Issues discussed include how and when to screen babies in hospital, what to do with a positive screen and how to screen babies born at home. The UK National Screening Committee is currently investigating the potential feasibility of routine PO screening in the UK, and so it is perhaps a suitable time for individual hospitals to consider the possibility of introducing such screening in their maternity units.