A Chinese married couple—who were desperately trying to conceive—learned they had been having sex the wrong way for four years.

The young pair, whose identities have been kept anonymous, went to see obstetrician Liu Hongmei after the woman failed to get pregnant despite having sex on a regular basis, reported the Guiyang Evening News. During their appointment, the woman admitted that sex was “usually painful,” which prompted Liu to perform a gynecological examination.

"The couple were very young, the man 26 and the woman 24. They were very healthy, but, despite being married for four years, couldn't conceive,” Liu said. "Their family was giving them a lot of stress because of it."

The results were unexpected. Liu discovered that the couple had mistakenly been having anal intercourse rather than vaginal to conceive. According to the Guiyang Evening News, Liu gave the couple a sex-education handbook and within months, the woman became pregnant. To show their appreciation, the two sent Liu a live hen and 100 eggs as a gift.

"Four years of marriage and neither the husband nor wife knew how to get pregnant. Couples so lacking in general knowledge are very rare," Liu said. "But it is not uncommon for people to lack or have misconceptions regarding sexual knowledge."

Although China’s alarming lack of sex education has been a widely discussed issue in recent years, little progress has been made to address the problem. Today, the topic of sex remains largely taboo in schools.

In May, Chinese students at Beijing Normal University held a demonstration demanding that the government provide better sex education for its youth. The protestors held signs that read “Adult videos can’t be our sex education, universities must say yes to sex education” and “We want to enjoy safe sex lives.”

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China’s National Center for STD/AIDS prevention found 115,000 new cases of HIV in 2015 across the mainland, 14.7 percent of those who tested positive were between 15 and 24 years old, CNN reported. A select number of universities now have vending machines that dispense home HIV testing kits.

"Machines alone can't solve the problem unless there's follow-up education to help students," Xiong Binqi, vice president of the Beijing-based 21st Century Education Research Center, said.

"Sex education faces great challenges in China," Jing Jun, a professor of sociology at Beijing’s Tsinghua University told CNN. "At Tsinghua, students take sex education classes where they learn basic knowledge about sex safety, condom use, etc. As far as I know, this is the first time most of my students have ever taken such a class."