Children struggling with their gender identity are waiting up to 18 months for an initial consultation at Scotland's only clinic, with the number of referrals up by 750% since 2013.

The long wait poses a challenge to those trying to understand their identity while struggling through puberty, and leaving families to grapple with difficult questions on their own.

Other mental health services across the country set an 18-week wait as the acceptable upper limit for initial appointments.

"So much happens to your body in your puberty over 18 months waiting and that causes real, intense distress for young people," said James Morton of the Scottish Trans Alliance.

"Families are left without any expert guidance on how to support their child, what to do, what not to do."

The Glasgow-based Sandyford Young People's Gender Service received 34 referrals in 2013, but last year 290 children were referred to the service. There are 470 children waiting for a first appointment.

Health minister Jeane Freeman and the clinic both refused to answer questions about the waiting times. Instead, a Scottish Government spokesperson responded to emailed questions.

"The current waiting time is unacceptable," the statement read. "We will work with the board to examine and resolve this issue."

The statement said the clinic was a "very specialised" resource and suggested there are other ways for families to get support such as through general practitioners and charities.

That's not good enough for Monica Lennon, a Scottish Labour MSP, who wants to see a review of the service to determine if it's meeting the needs of the children and families who are asking for help.

"In no other situation would it be acceptable to have to wait 18 months for a first appointment," she said, adding that a review could determine if the clinic is adequately staffed and if having one location makes it more difficult for families from across the country to access services.

Seven Hex experienced gender dysphoria - a condition where a person experiences discomfort or distress because there's a mismatch between their biological sex and gender identity - as a child and transitioned as an adult.

She said the long waiting exacerbates distress for already vulnerable children.

"It's really distressing because we live in a very gendered world where expectations are placed on you and that happens from very young," she said.

"It can be extremely distressing because firstly you realise you're not matching up and secondly to explain to others why you're not matching up.

"There's a deep sense of shame involved in that. It can be a very horrible and tough time."

A spokeswoman for NHS Greater Glasgow & Clyde said: "The young person's gender identity service at Sandyford is currently the only multi-disciplinary service of its kind in Scotland and is the only one in the country that sees patients from other health board areas.

"We have seen increasing demand in recent years with referrals up by 50% in 2015 and 57% in 2016. This led to the expansion of the service which is now delivered by a team staffed by Psychiatry, Psychology and Specialist Occupational Therapy."

She added: "The current waiting time for an initial consultation is approximately 18 months and we are making a concerted effort to reduce this as we had some vacancies in the service which have now been filled. The service also seeks to ensure patients are signposted to other services that may be able to offer support to people during the wait.

"We are committed to offering a positive experience for transgender people using sexual health services. We are determined to play a key role in ending the stigma people can experience and creating a better understanding of transgender issues."