A transgender woman has successfully breastfed a baby for the first time in recorded medical literature.
The patient's partner was the birth mother, but she wasn't keen to breastfeed, according to a new report in a medical journal.
The 30-year-old, who had been taking feminising hormones for six years but had not undergone any gender-related surgeries, sought the help of the Center for Transgender Medicine and Surgery.
"She hoped to take on the role of being the primary food source for her infant," wrote Tamar Reisman and Goldstein Zil in Transgender Health.
Over three-and-a-half months the woman was treated with a nausea drug called domperidone, which has been anecdotally linked to milk production.
They also upped her hormone intake, and used a breast pump to stimulate production.
Once the baby was born, she had full-size breasts and was able to produce 227g of milk a day - enough to keep the infant growing healthily for six weeks, when she began supplementing with formula.
"This is a very big deal," Boston University School of Medicine associate professor Joshua Safer told New Scientist magazine.
"Many transgender women are looking to have as many of the experiences of non-transgender women as they can, so I can see this will be extremely popular."
It's believed to be the first successful case of a transgender woman breastfeeding an infant.
"It's out there on internet forums, but there's a lot on the internet that's true or untrue to varying degrees," Assoc Prof Safer told New Scientist.
Whether it worked because of the hormones, the breast pump or a combination of both remains to be proven. The US Food and Drug Administration warns against using domperidone as a milk production stimulant because of its unknown effects on infants, and "its association with cardiac arrhythmias, cardiac arrest, and sudden death".
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The contents of the milk are yet to be assessed, but the baby's good health was confirmed by a paediatrician. The long-term effects, if there are any, remain unknown.
Dr Reisman and Dr Zil hope other transgender women will be able to breastfeed their babies in the future without fear of ill-effects on themselves or their children.
"Breastfeeding offers immunological, metabolic, and psychosocial benefits for both mother and infant… economic advantages by allowing families to save resources that might be devoted to formula and infant healthcare... [and] has been noted to facilitate mother-child bonding."