The Compendium of Caraka 4.8.23

4.8.23

sā cedapacārād dvayostriṣu vā māseṣu puṣpaṃ paṣyennāsyā garbhaḥ sthāsyatīti vidyāt; ajātasāro hi tasmin kāle bhavati garbhaḥ//

If due to improper conduct she sees menses in the second or third month, one should know that her embryo will not remain; for at that time the embryo has not acquired essence.