Yuri Semyonov's history "The Conquest of Siberia: An Epic of Human Passions" says:
Journeys to Siberia were always measured in years. In an old book the author, in order to make clear how long a journey through Siberia must take, told in all seriousness the following story:
The Empress Elizabeth desired to make the acquaintance of her most distant subjects, and commanded that six maidens should be sent to her at St Petersburg from Kamchatka. They were selected at Bolsheryetsk. The journey took so long that all became mothers before their arrival at Irkutsk. In spite of the dismissal of the officer accompanying them, they all reached St Petersburg again pregnant.
Elizabeth ruled from 1741 to 1762, when Bolsheryetesk was the seat of the regional commandant and the sea route to Okhotsk was already open. I assume that the maidens in question were Itelmen, natives of southern Kamchatka.
What's the origin of this story?