"Bakhmina is in a civilian clinic near Moscow. We are not disclosing where exactly she is for ethical reasons," a federal penitentiary service official told RIA Novosti.
Bakhmina, 39, former deputy head of the legal department of the now defunct oil company's Moscow unit, has been serving a six and a half year term on embezzlement and tax evasion charges since October 2006. Bakhmina, who has two children, is pregnant and is due to give birth in December.
Her lawyers and rights groups have demanded the woman be released.
Media reports on Monday cited the former executive's defense team as saying that her transfer from a clinic in the Russian Volga republic of Mordovia, where she was serving her prison term, to an apparently better maternity hospital could be part of a deal with penitentiary authorities, who could have promised her better hospital conditions and parole in the future in exchange for a pledge not to seek a pardon.
Bakhmina, who had maintained her innocence since being arrested in 2004, pleaded guilty on October 22 and requested to be pardoned. Some media said she withdrew her pardon request on October 24.
In September, a court in Mordovia turned down her request for parole despite her pregnancy and testimony to her good conduct in prison. It was the second such rejection by the court.
The penitentiary official said on Wednesday the woman is in good health condition, and her husband and lawyer have been in touch with her already.
Legal proceedings launched against Yukos in 2003, seen by many as politically motivated, resulted in the conviction of Bakhmina and other executives and shareholders of what was Russia's largest oil producer, including founder and CEO Mikhail Khodorkovsky.
