First of all, Liu Zhi, the Emperor of Han Huan, was a lucky man. Emperor Han chose liang ji after he was poisoned, but the eldest husband could not be depressed for a long time, so he plotted with the eunuchs to send troops to attack the Liang clique. Then it's the imperial power in hand and start enjoying it.
But he could not give birth to a son, before the age of twenty-nine, probably because Empress Liang had not given birth for fear of power transfer, and had always taken certain measures against other pregnant concubines, and later when Emperor Huan came to power, he could not give birth to sons, and there were only three daughters until his death. This also indirectly led to the fall of imperial power again, and there was a certain responsibility for the demise of the Han Dynasty.
The other is Song Renzong, which is the most difficult one. He was a good emperor, and the most unfortunate thing was that there was no successor, he had a daughter, that is, the son was born less and did not survive.
In the end, he could only adopt his own nephew to inherit the throne. In history, there are not many such cases, I obviously have fertility and there are many daughters-in-law, and the fertility period is still more than ten years or even decades, but I can't give birth. It's too hard.