Astanga Hrudaya
समेद्यमांसं मधु वा कट्यभ्यङ्गं च शीलयेत्। हर्षयेत्सततं चैनामेवं गर्भः प्रवर्द्धते॥२०॥
Her waist should be anointed with oil daily, and she must be kept happy always. By these, the fetus begins to grow and the fetus nourished.
english translation