Clarification on arishta word in punyahavachanam

While performing punyahavachanam as per Ashvalayana sutram, while seeking blessings from the brahmins, the yajamana prays -

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( Om, akshatam charishtam chastu )

Here, the term arishta is a little confusing. "Akshata means one that doesn't diminish.

Arishta in the ordinary sense means misery. It sounds like " let there be misery".

As per amarakosha

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  ( arishtam soothikaagaram)

Arishtam means the labour room ( room in which childbirth takes place ). The term arishtam implies child birth or continuance of the vamsha. That settles the confusion.