Astanga Hrudaya
इच्छन्ती भर्तृसदृशं पुत्रं पश्येत्पुरः पतिम्। ऋतुस्तु द्वादश निशाः पूर्वास्तिस्रोऽत्र निन्दिताः॥२६॥
should remain clean, and see her husband first, harboring the desire for a son resembling her husband Rutu (period suitable for conception) is twelve nights (day and night);
english translation
icchantI bhartRsadRzaM putraM pazyetpuraH patim। Rtustu dvAdaza nizAH pUrvAstisro'tra ninditAH॥26॥
hk transliteration by Sanscript