Srimad-Bhagavatam: Canto 3 - Chapter 1 - Verse 4


चतुर्भिर्धातव: सप्त पञ्चभि: क्षुत्तृडुद्भव: ।षड्‌भिर्जरायुणा वीत: कुक्षौ भ्राम्यति दक्षिणे ॥ ४ ॥


caturbhir dhātavaḥ saptapañcabhiḥ kṣut-tṛḍ-udbhavaḥṣaḍbhir jarāyuṇā vītaḥkukṣau bhrāmyati dakṣiṇe


Within four months from the date of conception, the seven essential ingredients of the body, namely chyle, blood, flesh, fat, bone, marrow and semen, come into existence. At the end of five months, hunger and thirst make themselves felt, and at the end of six months, the fetus, enclosed by the amnion, begins to move on the right side of the abdomen.


When the body of the child is completely formed at the end of six months, the child, if he is male, begins to move on the right side, and if female, she tries to move on the left side.