Often there are jokes around the Internet by Indians as well as foreigners on Dhitrashtr and Gandhari as to how they could manage 100 children. However, Indian mythology has its own mystics and so physical intimacy for 100 times certainly was not the cause. On the contrary, Kauravas were born from the lump of masses that Gandhari had delivered, courtesy Rishi Vyasa. Besides, the five children which were born back to back to Kunti and Madri were not due to physical intimacy but by the aashirwads and tathastus, thanks to various Gods again.
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So, how are the Gods involve in giving birth to Pandavas and Kauravas?
Well, Pandu had killed a sage in disguise as a stag mating with his wife disguised as a doe. He therefore was cursed by the dying sage that since he had killed a creature in its tenderest form he would die instantly too if he ever approaches a woman with a passionate intent. Saddened, he decides to leave Hastinapur and pursue the rest of his life in a forest as a hermit. However, after meeting several sages and gaining knowledge in the concept of salvation, he is startled to know that a man without children could never aim for heaven. He then seeks their blessings who bless him of many worthy sons.
Pandu then thinks of methods to have children and tells Kunti to beget children from illustrious men. Kunti too narrates the incident of her begetting a son from lord Surya as a girl from a mantr which she had received from Durvasa Rishi. Pandu is overjoyed after hearing this incident and he wishes his first son to be from Yama, the Lord of Justice as truth is the most superlative virtue any man may possess. So, this is how Yudhishtr is born to Kunti as soon as she chants the mantr and summons Lord Yama with waiting for the gestation period of nine months. When Yudhishtr was born, Dhritrashtr was still childless and so Yudhishtr became the eldest son of the Kuru dynasty.
When Gandhari got to know that Kunti delivered Yudhistr she beat her womb in frustration as her pregnancy prolonged for a very unusual time. She then did not deliver any baby but a lump of mass. Satyawati then approached King Vyasa who divided the lump into 100 equal parts. Kept each of them into the pots of ghee and sealed it into the earth for a period of 1 year. The show however shows that it was hanged and not buried unlike the tale. So, this is how the Kauravas were born, the first one being the Duryodhan.
Meanwhile, Pandu in the forest thinks that a man with only one son is equal to those who have none and so once again urges Kunti to beget a son and this time from Vyau, the Lord of the Wind. This is how Bheem is born exactly next day after the birth of Duryodhan. Next, is Arjun from Lord Indra.
Madri too desires children of her own and so Kunti teaches her the incantations and then Madri begets the twins, Nakul and Sehdev from the Ashwin brothers.
This is how the 105 children of the Kuru dynasty are born. Out of which 100 are Kauravas, the children of Dhitrashtr and 5 are of Pandavas, the sons of Pandu. One among the Kauravas is a girl who is called Dushala, which was granted to Gandhari from Lord Shiva after she had expressed her wish.