The Compendium of Caraka 4.8.6_1

4.8.6_1

nyubjāyā vāto balavān sa yoniṃ pīḍayati, pārśvagatāyā dakṣiṇe pārśve śleṣmā sa cyutaḥ pidadhāti garbhāśayaṃ, vāme pārśve pittaṃ tadasyāḥ pīḍitaṃ vidahati raktaṃ śukraṃ ca, tasmāduttānā bījaṃ gṛhṇīyāt; tathāhi yathāsthānamavatiṣṭante doṣāḥ/

In a prone woman, wind is forceful and compresses the vagina; in one lying on her side, if on the right side, phlegm is displaced and blocks the uterus; if on the left side, bile is compressed and burns up the ovum and semen; therefore, she should receive the seed lying supine, for thus the doṣas remain in their proper places.