Hundreds of test-tube babies have been born through artificial insemination in Japan since the first successful case in 1983.

CNN: AN HEIR OF CHANGE IN JAPAN

The cub, conceived through artificial insemination, was 14-year-old mother Mei Xiang's second in seven years with 15-year-old Tian Tian, the zoo's male giant panda.

CNN: Panda cub dies at Smithsonian's National Zoo

He also argued the scale of planning involved in providing a child for gay couples through donor insemination and surrogacy methods often makes them better parents than their heterosexual counterparts.

BBC: Gays 'have right to parenthood'