Palestinian prisoners in Israeli jails are smuggling out sperm in order to impregnate their wives, a fertility doctor has said, claiming that the wife of a prisoner serving 32 life sentences gave birth to a boy last August and four other prisoners' wives are pregnant after insemination.

Salem Abu Khaizaran, who works at a fertility clinic in Nablus, said 22 women had undergone insemination using smuggled sperm, but the success rate was low because of the difficulties of keeping sperm fresh during transportation from prisons in Israel to the West Bank.

Forty samples had been smuggled out of prisons, Abu Khaizaran claimed though he declined to explain how. The Israeli prisons service expressed scepticism over the doctor's account.

One of the pregnant women, Rimah Silawi, 38, told a news conference: "We women are growing old and our chances of having babies in the future is diminishing." Her husband, Osama, is serving four life sentences for the murders of an Israeli and three alleged Palestinian collaborators 22 years ago.

"The wives of prisoners are suffering," said Abu Khaizaran, who waives charges for the women's treatment at the Razan medical centre. "They feel they are lonely because their husbands are behind bars, some for the rest of their lives, and they are eager to have babies that can make a difference in their lives."

There are around 4,500 Palestinian prisoners in Israeli jails. Visits are restricted to 45 minutes, and no physical contact is permitted between husbands and wives. Prisoners are separated from their visitors by a glass panel, and only children up to the age of eight are allowed to touch their fathers. No conjugal visits are permitted.

"We doubt that something like this [the smuggling of sperm] can be done because of the security and rules for visitors for Palestinian prisoners," said Sivan Weizman, spokeswoman for the prisons service. "We doubt anyone got pregnant this way."

She pointed out that most prisoners' wives and relatives have to make long journeys to visit men in jail. "As we understand it, sperm cannot survive more than one hour outside the body or laboratory conditions."

Abu Khaizaran said he did not ask the prisoners' wives how they smuggled the sperm. But, he added, "there are many failed attempts because the sperm die and so prisoners have to keep trying until it works."

Dallal Ziben, whose husband Ammar was given 32 life sentences for a bombing in Jerusalem 15 years ago, gave birth by Caesarian section to a boy, Muhannad, last August, allegedly following IVF treatment with smuggled sperm.

"We received a sample of sperm from the husband in a reliable and clinically secure way," said Abu Khaizaran at the time. The couple, who already had two teenage daughters, wanted a boy "so we carried out a gender separation procedure. We tried the insemination three times from the same sample, but the first two attempts failed."

Although conjugal visits are forbidden for Palestinian prisoners, they are permitted for some Israeli prisoners. Yigal Amir, who is serving a life sentence for the assassination of Israel's prime minister Yitzhak Rabin in 1995, got married while in jail and was permitted a 10-hour conjugal visit in 2006 followed by regular monthly conjugal visits. His wife, Larisa Trombobler, gave birth to a boy in October 2007.