By Huizhong Wu

BEIJING (Reuters) - An unmarried Chinese woman filed a suit against a hospital on Monday for rejecting her request to undergo a medical procedure to freeze her eggs due to her marital status, in China's first legal challenge of a woman fighting for her reproductive rights.

According to China's laws on human assisted reproduction, only married couples can use such health services, and they must be able to prove their marital status by showing a marriage license.

Teresa Xu, 31, visited the Beijing Obstetrics and Gynaecology Hospital at Capital Medical University in November 2018, wanting to freeze her eggs while she focused on her career as a writer on gender issues.

A woman's eggs deteriorate in quality as she ages, presenting obstacles to conception among older women. Through a medical procedure, a woman's eggs can be removed from her ovaries and frozen for use at a later time.

Xu, from northeastern Heilongjiang province, said on her first visit to the hospital for a checkup, the doctor asked about her marital status and urged her to have a child now instead of freezing her eggs.

Upon her second visit, the doctor told her she could not proceed any further.

"I came here for a professional service, but instead I got someone who was urging me to put aside my work and to have a child first," she said. "I have already received a lot of this pressure in this society, this culture."

When asked by Reuters to comment, the hospital declined, saying it could not speak to international media.

China's rapid economic growth has created the conditions for single women to become financially independent, but the country's policies and medical industry have not necessarily kept pace.

"This is a systemic issue, because the system has brought this difficult position for single women," Xu said.

She considered illegal clinics.

The women's bathroom door at the hospital, Xu said, was filled with these ads.

But ultimately she decided against it.

Those who can afford it have circumvented China's strict laws on fertility by going abroad. Xu said she had made enquiries but found it too expensive.

Agents told her that a treatment in Thailand would cost about 100,000 yuan ($14,273) and 200,000 yuan if she wanted to undergo the treatment in the United States.

Xu said her case was expected to go on for several months.

"I personally feel that being able to arrive at this stage is already a sort of win," she said.

"For me I didn't feel like I was at court as an individual. I felt I was standing there with the weight of many other single women's expectations."

($1 = 7.0063 Chinese yuan renminbi)

(This story corrects to remove erroneous reference to marriage laws in headline, paragraph 1.)

(Reporting by Huizhong Wu; Editing by Ryan Woo and Michael Perry)