Former hostage Joshua Boyle says his wife Caitlan has been rushed to the hospital, less than a week after the couple and their three children were rescued.
Mr Boyle told The Associated Press in an email his wife was admitted on Monday, and remains in hospital.
Mr Boyle, his American wife and their three children were rescued on Wednesday, five years after the couple was abducted in Afghanistan on a backpacking trip.
"My first concern has to be the health of my wife and children," Mr Boyle wrote.
His email, sent on Tuesday, did not specify why his wife was taken to the hospital.
After landing at Toronto's airport following their rescue, Mr Boyle said the Taliban-linked Haqqani network raped his wife and murdered a fourth child during the years they were held captive.
In prior email exchange with AP, Mr Boyle did not respond to a question about the fourth child but later told Canadian Broadcasting Corporation it was a forced abortion.
The Taliban said in a statement it was a miscarriage.
On Monday, Mr Boyle said he and his wife decided to have children even while held captive because they always planned to have a big family and decided, "Hey, let's make the best of this and at least go home with a larger start on our dream family".
"We're sitting as hostages with a lot of time on our hands," he said.
"We always wanted as many as possible, and we didn't want to waste time. Cait's in her 30s, the clock is ticking."
All of the couple's children were born in captivity.
Mr Boyle said the children were now four, two, and "somewhere around six months".
Ms Boyle's parents said they were elated she was free, but also angry at their son-in law for taking their daughter to Afghanistan.
"Taking your pregnant wife to a very dangerous place, to me, and the kind of person I am, is unconscionable," Caitlan's father Jim Coleman said.