The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
19. It is, moreover, recorded in the (ordinary) world.
There are, moreover, traditions, apart from the Veda, that certain persons like Drona, Dhrishtadyumna, Sîtâ, Draupadî, &c., were not born in the ordinary way from
mothers. In the case of Drona and others there was absent the oblation which is made into the woman; while in the case of Dhrishtadyumna and others, even two of the oblations, viz. the one offered into woman and the one offered into man, were absent. Hence in other cases also birth may be supposed to take place independently of the number of oblations.--It is, moreover, commonly known that the female crane conceives without a male.