OBJECTIVES: To determine the cost to the NHS resulting from multiple pregnancies arising from IVF treatment in the UK, and to compare those costs with the cost to the NHS due to singleton pregnancies resulting from IVF treatment. DESIGN: A modelling study using data from published literature and cost data from national sources in the public domain, calculating direct costs from the diagnosis of a clinical pregnancy until the end of the first year after birth. SETTING: Academic Unit of Reproductive and Developmental Medicine. POPULATION: Theoretic core modelling study using data from published literature. METHODS: The analysis was based on the total annual number of births resulting from an IVF treatment in the UK. Main outcome measures total direct costs to the NHS per IVF singleton, twin or triplet family. MAIN OUTCOME MEASURES: Cost of singleton, twin and triplet IVF pregnancies in the UK. RESULTS: Total direct costs to the NHS per IVF twin or triplet family (maternal + infant costs) are substantially higher than per IVF singleton family (singleton: pounds 3313; twin: pounds 9122; and triplet: pounds 32,354). Multiple pregnancies after IVF are associated with 56% of the direct cost of IVF pregnancies, although they represent less than 1/3 of the total annual number of maternities in the UK. CONCLUSIONS: Multiple pregnancies after IVF are associated with high direct costs to the NHS. Redirection of money saved by implementation of a mandatory 'two embryo transfer' policy into increased provision of IVF treatment could double the number of NHS-funded IVF treatment cycles at no extra cost. Further savings could be made if a selective 'single embryo transfer' policy were to be adopted.