Information about gestational age is important but is not available for live births from registration data. It is, however, collected in NHS Numbers for Babies (NN4B) records. This project investigates the feasibility of linking NN4B data for births in the First quarter of 2005 with birth registration records. Overall 99.8 per cent of NN4B records linked with a registration record. Accuracy of linkage was questioned in 0.9 per cent. Live/stillbirth and multiple birth status were each differently classified in approximately 1 per 1,000 records. Discordance rates for other individual data items ranged from 0.3 per cent for date of birth to 12.9 per cent for postcode. Although needing further investigation, these results justify extending the linkage to the remainder of births in 2005. Linkage would be improved by retaining NHS numbers on stillbirth registration records and avoiding manual transfer of NHS numbers.