A transgender woman has become the first in the world to exclusively breastfeed her baby despite not giving birth nor undergoing gender-reassignment surgeries.

The 30-year-old woman, who has not been identified, told doctors at Mt Sinai's Center for Transgender Medicine and Surgery that her partner was pregnant but did not wish to breastfeed, and she hoped to try instead.

For three-and-a-half months before the birth, the woman was put on a dose of hormone replacement therapy which the patient obtained from Canada, as well as breast pumping, until she could produce eight ounces of milk a day.

By the time the child was born, the patient was producing enough milk to exclusively nurse for six weeks, then continued breastfeeding alongside other food sources for six months.

Uniquely, she hadn't had any gender reassignment surgeries like a breast augmentation or a vaginoplasty to construct a vagina or vulva, which can change a person's hormone levels and in theory affect the ability to breastfeed.

The 30-year-old woman, who is not identified, told Mt Sinai's Center for Transgender Medicine and Surgery that her partner was pregnant but did not wish to breastfeed, and she hoped to try instead (file image)

The case study, published today in the journal Transgender Health, is the clearest evidence to date that DIY hormone therapy can allow transgender women the experiences of childbirth and pregnancy.

'We believe that this is the first formal report in the medical literature of induced lactation in a transgender woman,' the authors wrote.

Speaking to Daily Mail Online, the patient's doctor Tamar Reisman, MD, said the milestone was a breakthrough for transgender medicine, adding: 'We are happy that the patient shared her experience with us, and we are happy to help our patients build happy, healthy, transgender families.'

The patient, who was in good health with no medical issues, had started a hormone regimen independently of Mt Sinai in 2011.

She was taking a testosterone suppressor called spironolactone, estradiol which is near-identical to the hormones produced by ovaries, and micronized progesterone.

When the patient came to the center, she told Dr Reisman and program manager Zil Goldstein she had obtained domperidone from Canada.

The drug, commonly used around the world for gastric procedures and to induce lactation, is not approved by the FDA but is commonly used by Americans in 'DIY hormone therapy'.

Dr Reisman said that the FDA's reluctance to approve domperidone is partly to do with reports of patients injecting the gastric drug intravenously, and developing cardiac issues. Regulators also harbor unsubstantiated concerns that we do not know how it affects breast milk, though no studies have found reason for concern.

The medical team started the patient on 10mg a day of domperidone, as well as five minutes a day of breastfeeding.

Within a month, she was producing droplets.

They upped the dosage to 20mg a day, while doubling her increasing her 'feminizing hormones' (micronized progesterone and estradiol), plus an extra breast pump per day. A month later, they increased her progesterone and estradiol doses once again.

By the third month, two weeks ahead of the baby's due date, she was producing eight ounces of milk a day, and was able to lower her progesterone and estradiol doses.

The baby, who was born weighing 6lbs 13oz, was then breastfed exclusively for six weeks, and doctors reported the child was healthy and developing at the same rate as other babies.

Dr Reisman said it is possible the mother could have produced breastmilk with a breast pump alone, and that the domperidone was merely supplementary.

It's an area she is keen to investigate, though it will require a randomized control trial, and that depends on garnering enough interest to compare different methods.

For now, Dr Reisman said, she is happy to have reached this breakthrough with this patient.

'We know that breastfeeding has a lot of benefits,' she said, referring to the scores of research that show babies breastfed for the six months of their life tend to have better digestive health and immunity.

'That doesn't mean that all patients have to want to breastfeed, but for this patient in particular it was the right choice and I'm happy we could help.'