A Nigerian city with an unusually high number of twins has celebrated the phenomenon at an annual festival.

Nearly every family in the south-western city of Igbo-Ora has twins or other multiple births, according to local chief Jimoh Titiloye.

For the past 12 years, the community has organised an annual festival to celebrate twins.

This year’s event, held earlier this month, included more than 1,000 pairs of twins and drew participants from as far away as France, organisers said.

There is no proven scientific explanation for the high rate of twins in Igbo-Ora, a city of at least 200,000 people 83 miles south of Nigeria’s largest city, Lagos.

But many in Igbo-Ora believe it can be traced to women’s diets. Alake Olawunmi, a mother of twins, attributes it to a local delicacy called amala which is made from yam flour.

John Ofem, a gynaecologist based in the capital, Abuja, has said it could be “that there are things they eat there that have a high level of certain hormones that now result in what we call multiple ovulation”.

While that could explain the higher-than-normal rate of fraternal twins in Igbo-Ora, the city also has a significant number of identical twins.

Those result instead from a single fertilised egg that divides into two – not because of hyper-ovulation.

Taiwo Ojeniyi, a Nigerian student, said he attended the festival with his twin brother “to celebrate the uniqueness” of multiple births.

“We cherish twins while in some parts of the world, they condemn twins,” he said. “It is a blessing from God.”