The doe was pregnant, and when it jumped out of fear, the baby deer fell from its womb into the flowing waters of the river.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
तस्या उत्पतन्त्या अन्तर्वत्न्या उरुभयावगलितो योनिनिर्गतो गर्भः स्रोतसि निपपात
tasyā utpatantyā antarvatnyā urubhayāvagalito yoninirgato garbhaḥ srotasi nipapāta
SB 5.8.5