1. Institute of Reproductive and Developmental Biology (L.J.W., S.A.S., K.H., S.F.), Imperial College London, United Kingdom
2. Department of Mathematics (J.S.), Imperial College London, London SW7 2AZ, United Kingdom
3. Reproductive Medicine Unit (R.A.M., G.H.T., S.A.L.), Hammersmith Hospital, London W12 0NN, United Kingdom