In 637 AD, Wu Zetian, who was 14 years old, became a member of Li Shimin of Emperor Taizong, and Li Shimin was forty years old this year. There are many children in Li Shimin. Li Shimin, 40, should have no physical problems. At the same time, Wu Zetian had six children in her life, and her health should be fine. Wu Zetian was a little young when she first entered the palace, so why didn't Wu Zetian and Li Shimin 12 have children?
Wu Zetian missed the chance to get pregnant because of her young age. Wu Zetian, 14 years old, was heard by Li Shimin of Emperor Taizong and put into the harem. Newcomers should have been favored by Li Shimin when they entered the palace, but because Wu Zetian was still young and immature, it was difficult to get pregnant. So Li Shimin did it on purpose.
Wu Zetian entered the palace at the age of 14, and followed Emperor Taizong and Li Shimin at the age of 12. When Li Shimin died, Wu Zetian was still a low-ranking person, which shows that Wu Zetian was not liked by Li Shimin at all. It is very likely that Wu Zetian was snubbed by Li Shimin, and it is difficult for Wu Zetian to get Li Shimin's favor when she matures. No matter how good the land is, crops cannot grow without seeds. Li Shimin does not allow Wu Zetian to have children. Wu Zetian is a ruthless woman neglected by Li Shimin. So Li Shimin doesn't want this.