Vichitravirya was still a child when he was crowned king, thus Bhishma ruled as his regent. When the young king became at proper age to marry, Bhishma searched for him for a suitable bride. And he heard the king of Kasi was holding a swayamvara for his three daughters. Since Vichitravirya himself was yet too young to stand any chance of being chosen by the young women, Bhishma himself went to the swayamvara.
Bhishma won the swayamvara and brought the Princesses Amba, Ambika and Ambalika to marry Vichitravirya. But Amba had already given her heart to another, therefore Ambika and Ambalika were married to Vichitravirya.
Unfortunately, shortly after his marriage, Vichitravirya died of consumption tuberculosis. As he died heirless, Vyasa was summoned to subsequently father Pandu, Dhritarashtra and Vidura.
Vyasa came to help Ambika and Ambalika have children with his Yogic power. Vyasa told that they should come alone near him. First did Ambika, but because of shyness and fear she closed her eyes. Vyasa told Satyavati that the child will be blind. Later this child was named Dhritarashtra. Thus Satyawati sent Ambalika and warned her that she should remain calm. But Ambalika's face became pale because of fear. Vyasa told that child will suffer from anaemia, and he will not be fit enough to rule the kingdom. Later this child was known as Pandu. Then Vyasa told Satyavati to send one of them again so that a healthy child can be born. This time Ambika and Ambalika sent her maid in the place of themselves. Maid was quite calm and composed during the Yogic process, and so she got a healthy child later named as Vidura.