Matsya Purana — The Madana-Dvādaśī Vow and the Birth of the Maruts
यस्तु तस्या भवेत्पुत्रः शीलायुर्वृद्धिसंयुतः अन्यथा गर्भपतनम् अवाप्नोति न संशयः //
yastu tasyā bhavetputraḥ śīlāyurvṛddhisaṃyutaḥ anyathā garbhapatanam avāpnoti na saṃśayaḥ //
But the son who is born to her will be endowed with good conduct, longevity, and increasing prosperity; otherwise, miscarriage (loss of the embryo) is incurred—of this there is no doubt.
This verse does not address Pralaya; it focuses on household ethics and the karmic/ritual conditions believed to influence the well-being of offspring.
It reinforces Gṛhastha-dharma: right conduct and proper observances are portrayed as leading to virtuous, long-lived, and prosperous progeny, while violations are said to result in pregnancy loss.
No Vāstu or temple-architecture rule appears here; the ritual significance is ethical-ritual causality around conception and pregnancy outcomes (garbha-related injunctions).