What baby's wrapped in, returning home in a day (6)

I believe the answer is:

amnion

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'what baby's wrapped' is the definition.
I can't tell whether this definition defines the answer.

'returning home in a day' is the wordplay.
'returning' is a reversal indicator.
'home' becomes 'in' ('he's home' can mean 'he's in').
'in' means one lot of letters goes inside another.
'day' becomes 'mon' (abbreviation for Monday).
'in' in reverse letter order is 'ni'.
'a'+'mon'='amon'
'ni' going within 'amon' is 'AMNION'.

'in' is the link.

Can you help me to learn more?

(Other definitions for amnion that I've seen before include "One embryo membrane" , "Innermost membrane" , "Film about site of early growth" .)

I've seen this clue in The Independent.

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