Image copyright Courtesy of Rebecca Dixon Image caption The Dixon family learned this year Daniel was not Rebecca's biological father.

A Canadian fertility doctor is being sued by dozens of people who claim he used his own or unknown sperm to impregnate their mothers.

In November Dr Norman Barwin was sued after a DNA test said he was the father of a former patient's daughter.

At least 11 others now claim he is their biological father, lawyers say.

The group filed a class-action lawsuit with about 50 offspring of former patients whose DNA does not match their intended biological father.

The claims go as far back as the 1970s, and include patients from at least two fertility clinics in Ottawa, Ontario - Broadview Fertility Clinic and Ottawa General Hospital.

Dr Barwin's lawyer Karen Hamway declined to comment on the recent allegations.

Lawyers Peter Cronyn and Frances Shapiro Munn say they have found 11 people whose parents went to Dr Barwin for fertility treatment who are allegedly his biological children, according to DNA tests. In some cases, they were supposed to be conceived with an anonymous donor, in others with their mother's spouse.

They have also found 16 other people who were supposed to be conceived using their father's sperm where DNA tests reveal they are not a biological match to their father.

In these cases, the biological father is unknown, according to Mr Cronyn and Ms Shapiro Munn.

There are also 35 people who were supposed to be conceived using anonymous donor sperm who may not be a biological match with the intended donor, the lawyers claim.

Image copyright CBC Image caption A lawsuit alleges Dr Norman Barwin used his sperm to impregnate at least two of his fertility clinic patients

News about the allegations came to light last November, when Daniel and Davina Dixon and their daughter Rebecca filed a civil lawsuit against Dr Barwin with Nelligan, O'Brien and Payne in an Ontario court. The lawyers say they will be updating their statement of claim with the new claimants.

The family decided to take legal action after learning that Rebecca was not Mr Dixon's biological daughter. The Dixons contacted Dr Barwin in 1989 to help them get pregnant and Rebecca was born a year later.

"[Davina] was concerned because she and Daniel have blue eyes and Rebecca has brown eyes," the statement of claim said.

They later found a possible half-sister of Rebecca's, whose mother was also a patient of Dr Barwin.

Dr Barwin was previously sanctioned in 2013 for artificially inseminating three patients with the wrong sperm at his Ottawa clinic.

None of the recent allegations against Dr Barwin have been proven in court.