Hiranyakeshigrihyasutra 1.7.25

(a) 'May Vishnu make thy womb ready; may Tvashtri frame the shape (of the child); may Pragâpati pour forth (the sperm); may Dhâtri give thee conception!
(b) 'Give conception, Sinîvâlî; give conception, Sarasvatî! May the two Asvins, wreathed with lotus, give conception to thee!
(c) 'The embryo which the two Asvins produce with their golden kindling-sticks: that embryo we call into thy womb, that thou mayst give birth to it after ten months.
(d) 'As the earth is pregnant with Agni, as the heaven is with Indra pregnant, as Vâyu dwells in the womb of the regions (of the earth), thus I place an embryo into thy womb.
(e) 'Open thy womb; take in the sperm; may a male child, an embryo be begotten in the womb. The mother bears him ten months; may he be born, the most valiant of his kin.
(f) 'May a male embryo enter thy womb, as an arrow the quiver; may a man be born here, thy son, after ten months.
(g) 'I do with thee (the work) that is sacred to Pragâpati; may an embryo enter thy womb. May a child be born without deficiency, with all its limbs, not blind, not lame, not sucked out by Pisâkas.
(h) 'By the superior powers which the bulls shall produce for us, thereby become thou pregnant; may he be born, the most valiant of his kin.
(i) 'Indra has laid down in the tree the embryo of the sterile cow and of the cow that prematurely produces; thereby become thou pregnant; be a well-breeding cow'—
And (besides with the two Mantras), 'United are our names' (above, 24, 4), and, 'The concord of the kakravâka birds' (24, 6).

(He should cohabit with her with the formulas), 'Bhûh! Through Pragâpati, the highest bull, I pour forth (the sperm); conceive a valiant son, N.N.! Bhuvah! Through Pragâpati, &c.—Suvah! Through Pragâpati, &c.' Thus he will gain a valiant son.

The Mantras ought to be repeated whenever they cohabit, according to Âtreya,

Only the first time and after her monthly courses, according to Bâdarâyana.