Rates of incarceration among transgender Americans are significantly higher than for the general population, according to a 2011 National Transgender Discrimination Survey, which found that 16 percent of the nearly 6,500 respondents reported having ever been incarcerated, mostly for less than a year, in county jails.
This far exceeds the 2.7 percent of all Americans who have reported being imprisoned.
A study of California's men's prisons identified more than 330 transgender inmates out of a population of approximately 160,000. All these inmates were transgender women.
In federal prisons, guidelines for housing of transgender inmates in sex-segregated facilities are regulated by the Prison Rape Elimination Law.
Manning's lawyer, David Coombs, said his client's goal was not to be placed in a women's prison. Rather "the ultimate goal is to be comfortable in her skin, and to be the person that she's never had the opportunity to be," according to an interview on the "Today" show.
Coombs said he hoped Fort Leavenworth "would do the right thing and provide" the hormone treatments. If not, he said he would "do everything in my power to make sure that they are forced to do so."
Masen Davis, executive director of the Transgender Law Center in Oakland, Calif., told ABCNews.com that its attorneys were "looking at every recourse that Manning will have in military prison" to obtain necessary medical treatment.
"He has a right to access to care, including a prescription for estrogen," she said. "Medical treatment should be determined by a doctor, and not bias against trans people."
The Washington, D.C.-based Human Rights Campaign also weighed in on the issue with a statement today:
"Regardless of how she came to our attention, Pvt. Chelsea Manning's transition deserves to be treated with dignity and respect," the statement read.
"As Pvt. Manning serves her sentence, she deserves the same thing that any incarcerated person does -- appropriate and competent medical care and protection from discrimination and violence.
"The care she receives should be something that she and her doctors -- including professionals who understand transgender care -- agree is best for her."
ABC News' Luis Martinez contributed to this story.