His brother also agreed to have a DNA test. It established that the brother could not have been the baby's father.
The scientists, who give details of the unusual case in tomorrow's British Medical Journal, warn that although the risk is very small, couples should understand that pregnancies can happen.
The Journal says: 'A man may naturally be shocked when his wife becomes pregnant after he has had a vasectomy and he might wonder if she has been unfaithful. But no man should jump to such conclusions.'Reuse content