Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 2 · Signs, Planets, Birth
जातकम् १
ओजभे पुरुषांशेऽर्केज्येंदुलग्नैर्बलान्वितैः ।गुर्वर्कौ विषमस्थौ वा युंजन्म प्रवदेत्तदा ॥ ५१ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 55, verse 51.
The lagna (rising sign), the Sun, Jupiter and the Moon are strong. They are in an odd sign and a male navamsha (one-ninth part of a sign). Or Jupiter and the Sun are in odd signs. Then say that a boy is born.
Simple meaning: A boy is born when these planets are strong in odd signs and male navamsha.
युग्मभांशस्थितैस्तैस्तु वक्रेंदुभृगुभिस्तथा ।
A girl is born when those planets are in even signs, or Mars, Moon and Venus are in even places.
द्व्यंगस्था बुधसंदृष्टाः स्वपक्षेय मलंकराः ।
Planets in dual signs seen by Mercury can give twins. Saturn in an odd house away from the lagna gives a boy.
मिथो रवींदूर्ज्ञार्की वा पश्यतः समगं रविः ।
These sights and odd-even placements are conditions; the next verse gives the result, a neuter birth.