In 2008, doctors reported a curious case report about a woman who gave birth despite the majority of her cells having XY chromosomes, typically held by people who are biologically male.
A woman from Croatia sought medical attention when at 17-years-old she had not yet developed breasts, nor had her first period. Upon examination, the doctors didn't find much out of the ordinary, aside from the absence of these signs of female puberty. Her genitals appeared normal, she had pubic hair and facial acne, was tall, thin, and intelligent.
The only sign other unusual medical sign apparent to the doctors was that she had a hypoplastic uterus (her uterus was abnormally small). However, when they looked at her blood, they found that she had 46,XY, a disorder of sex development.
Typically (but not always) biologically male individuals have one X and one Y chromosome (XY) while those who are biologically female have two X chromosomes (XX). In people who have the 46,XY disorder of sex development (aka Swyer syndrome), individuals have external female genitalia and some internal female genitalia, though their cells have XY chromosomes (the chromosomes typically found in male individuals).
People with 46,XY tend to have a female gender identity and are raised as girls from birth (given their female external genitalia) by their parents. However, without functioning ovaries, as was the case in the girl from Croatia, those with the syndrome tend to go through hormone replacement therapy to begin puberty, and do not produce eggs of their own (though they can give birth with donated eggs).
What is interesting in this case (as flagged up by a great Twitter thread from the Vagina Museum) is that the mother was 46,XY too according to a karyotype on her blood, and had gone through female puberty and given birth to her daughter despite the majority of her cells containing XY chromosomes.
The team examined the mother, who had a typical female appearance, breasts, and external genitalia, though her pubic hair was sparse. She had been pregnant twice in her life, with the first resulting in miscarriage, and the second resulting in her daughter (via c-section, after her hip was injured in a car accident).
Though her blood was found to be 46,XY, samples taken from elsewhere around her body were not so. Cells in her skin were found to be 80 percent 46,XY and 20 percent 45,X, indicating Turner Syndrome with mosaicism. This is where female individuals are missing an X chromosome in some cells but not others. Where one chromosome is missing from all cells, it is simply Turner Syndrome, and can cause much more prominent symptoms, such as a webbed neck, heart defects, swollen limbs, and infertility.
More interestingly, her ovaries were found to be predominantly 46,XY (93 percent 46,XY and 6 percent 45,X), i.e. her ovaries contained chromosomes typically found in the cells of male individuals.
"We believe that our case of fertility in a female with a predominantly 46,XY karyotype in the ovary is unprecedented," the team wrote in the case report. "The fact that this mother had normal functioning ovaries, menstruated regularly, and achieved unassisted pregnancy twice is remarkable," they add.
People with Turner syndrome can give birth in about 2 percent of cases, the team report, however, they don't believe there is any reported case of someone with predominantly 46,XY chromosomes in their ovaries giving birth without assistance. They believe that there could be others out there, given that people who have given birth naturally may never discover the unusual chromosomes within their cells, having felt no need to check it out.