The risk is slight and pregnancies are rare, but 1 in 2,000 men who have had the operation could still produce small numbers of viable sperm, according to a report tomorrow in the Lancet.
The cases of six men who became fathers after vasectomies came to light when their partners became pregnant. None had any detectable sperm in their semen many months after the operation.
Joseph Smith, consultant urologist at the Churchill Hospital, Oxford, says the paternity of the fathers was proved by DNA analysis. In all six cases the men had produced two consecutive negative sperm counts after vasectomy, and the couples were told they could stop using contraceptives. The pregnancies occurred one to five years later.
Male fertility may not be declining, despite recent reports that sperm counts have dropped by nearly half in the last 50 years, doctors say in a report in the British Medical Journal.
The claimed fall in sperm counts is more likely to be attributed to a stricter definition of what is a normal sperm concentration.Reuse content