The first scientific case study has been published describing how a US transgender woman was able to breastfeed her adopted infant by taking hormones that induce lactation.
But experts say more research is needed to determine if the milk is nutritious and safe for babies.
The report in the journal Transgender Health describes a 30-year-old transgender woman who was born male and had been taking feminizing hormone therapy for six years. She had not undergone any genital or breast surgeries.
She sought medical advice because her partner was pregnant but was not interested in breastfeeding "and she hoped to take on the role of being the primary food source for her infant," said the report, led by researchers at Mount Sinai Icahn School of Medicine in New York.
The patient followed a regimen previously shown to induce lactation in women, including increased estradiol and progesterone, and was told to use a breast pump for five minutes per breast three times a day.
She also obtained an anti-nausea drug called domperidone from Canada that is used off-label to boost milk production.
Domperidone is not approved in the United States, due to the US Food and Drug Administration's concern that it may lead to cardiac arrest — and its unknown risks to breastfeeding infants.
"Three and a half months after she started the regimen, the baby was born," said the report.
"The patient breastfed exclusively for six weeks," then began to supplement feedings with formula due to "concerns about insufficient milk volume."
The baby's growth and feeding habits were all normal, said the report.
Experts say infants should be breastfed exclusively for the first year of life and longer if possible, due to the health benefits of mother's milk which far exceed formula.
But it's too early to say whether the transgender approach is safe and nutritious for infants, said Madeline Deutsch, clinical director of the University of California, San Francisco Center of Excellence for Transgender Health.
"I wouldn't do it," said Deutsch, herself a transgender woman and parent to a six-month old baby who is breastfed by Deutsch's wife, who was also the gestational carrier.
"The number one concern for me would be the nutritional quality," she told AFP.
Also, the hormones involved in inducing lactation can lead to mood swings and weight gain, which can be a deterrent for some people, she said.
A bit more research could easily shed light on the nutritional quality of the breast milk, and the safety of the hormones needed to produce it.
Besides, Deutsch said, efforts to coax transgender women to lactate have been going on informally within the transgender community for some time.
"I need to be honest with you, this has been happening for at least 10 to 15 years at least to my knowledge," she told AFP.
"This is just the first time somebody wrote it up."
As for whether fathers might one day decide to produce breast milk for their babies, Deutsch said that prospect seems far-fetched.
"I think it would be pretty unlikely that there would be too many men who are happy as men lining up to induce lactation," she said.
"Because the hormones involved would feminize the body significantly."