It was early November when John and Mary stopped by Baker Street looking exceptionally depressed, tired, and down right awful. John let himself in with the key he had kept from three years ago when he was last living in 221b. Sherlock was upstairs playing a particularly beautiful piece on his Violin, which John guessed was probably Bach. The Watsons walked in and Sherlock kept on playing another few bars until he reached the end of the allegro from what was indeed Bach's sonata no.1 in g minor, the last few notes ringing out in the air.
The detective placed the valuable 18th century Violin carefully on his armchair, before turning around to greet his best friend and his best friend's wife. They both looked like they were in particularly bad spirits today. Neither of them were looking at the other whilst they hanged up their hats and coats on the newly acquired coat rack. Mary looked even more sad than John, and something Sherlock can only perceive as guilt showed in her eyes.
One week ago John had confided in Sherlock that he and Mary had been trying to conceive their first child for over a year now, and were as of yet having no luck. He said that they were going to go to a fertility clinic next week so they could try and shed some light on their problem. Sherlock had managed to deduce that they were trying for a baby a few months earlier, but hadn't said anything. John said that Mary hadn't wanted anyone to know that they were trying to conceive, so the doctor begged Sherlock not to tell Mary he knows. This information combined with the fact that Mary looked sadder than John as well as guilt-ridden, led him to assume that their must be something wrong with Mary's body and not John's sperm.
The detective walked into the kitchen, put the kettle on, and came back to see John hugging a lightly crying Mary on the sofa. John looked up to Sherlock and gently released Mary from his embrace. Mary wiped her eyes and turned her attention to Sherlock, who had brought his armchair opposite the sofa and taken a seat.
Pretending he hadn't deduced why the couple were so upset, Sherlock asked "What's happened?"
John gave him a tight but kind smile. He then turned to his wife and, after she gave a consenting nod, began to retell Sherlock what they had been trying to do for the last fourteen months.
"Mary and I have been trying to have a baby for a year now, so we went to a fertility clinic today. My sperm is fine, but unfortunately it will be impossible for us to have a baby naturally. Mary's uterus will not allow her to carry any children, and her eggs never reach the maturity required to be suitable for conception."
After listening to all of what John had to say, Sherlock was somewhat surprised to hear just how dire Mary's fertility situation was. In theory they could treat her, but it could take a while and pregnancy at her age came with a higher risk of a miscarriage.
"We are going to look into a combination of surrogacy and donor conception now so if we did have a child then he or she would at least have genetic relations to one of his parents. If we don't find a surrogate we like then we are going to adopt. John and I are desperate to have a child Sherlock, I can't believe that it is going to be so hard!" Mary's eyes then started to water again, but she quickly wiped them with her sleeve.
"We will only use a surrogate if we like them and know them first, and the same goes for the egg donor. I once treated a little boy who came into the world through donor conception, and because his parents didn't know the genetic father, they didn't know a lot of the child's family history. When he was seven he was taken into hospital for headaches that turned out to be a brain tumour that tends to be genetically recurring. If anyone had told his family that he was at risk then that child would have been saved so much pain. I don't want to put that risk on a kid."
John looked to Mary for support in this and she nodded firmly. After hearing this Sherlock tried to think of anyone who would possibly be a surrogate for Mary and John. There was Molly, of course, who would almost certainly be kind enough to give up her uterus for nine months to allow Mary and John to have a child. Mary's friend Janine might have done it in the past, if Sherlock hadn't broken up their fake relationship in one of the cruelest ways possible. Mary didn't have many other friends, and certainly none that are close enough for her to consider asking them to be her surrogate.
John could ask Harry, but it probably wouldn't be a good idea to allow an alcoholic to carry a baby, no matter how much she says she has 'recovered'. Candidates for the egg donor is even more tricky for Sherlock to think of. Molly probably wouldn't do it, it would be too strange for her to have a child that was genetically both her's and John's. Again it is possible for Harry to be an egg donor, but if that were to happen then John wouldn't be able to be the Father.
An unbidden thought springs into Sherlock's mind. He knew that he was born a rarity. A freak, is what anyone who has come anywhere close to sleeping with Sherlock had said. He had been born with two sets of reproductive systems, both male and female, one behind the other. He was a True Hermaphrodite, intersex, whatever you want to call it.
Growing up no one suspected much until he was about twelve. All of his teachers thought he was a boy, all of his classmates thought he was a boy, and that was all that really mattered to him. Then came the horrors of puberty. Sherlock had the amazing idea during the summer of his eleventh year on this planet that he would learn four years worth of school work in one summer holidays. Mycroft bet him his Microscope that he couldn't do it, but that just made him more and more determined.
He studied and studied until finally he was at the same academic level as fifteen year olds. When he went to school he was top of the class. A class full of older, broader, deeper voiced boys. When he was twelve his chest started to get slightly larger. One day he looked in the mirror and saw two small, but undoubtably there, breasts developing on his chest. When he saw this he ran down stairs to where his Mother was in the Kitchen cooking breakfast and dragged her up to his room. He turned around and shut the door as soon as she was inside. Unable to help it, Sherlock's chin started wobbling and he realised he was dangerously close to crying.
He explained to his mum what was happening to his body, and Mrs. Holmes brought him to her chest and comforted her son in his distress. She told him that she would book an appointment at the doctors to see what they could do. A week later Sherlock was coming out of the special clinic they were referred to with enough Testosterone for him to inject into himself to last him for three months.
The doctor he saw was called Dr. Clarke, an amazing woman who was doing amazing things in the field of Gynaecology and Gender Identity. Back then she was scorned for her work because there were a lot more homophobic and transphobic arseholes around back then. She was young, tall, blonde, skinny, and beautiful though, so the men in her field let her have her way more often than they didn't. No one would guess that inside of her she had a testis as well as two ovaries, which the discovery of inspired her to do incredible work in her field of medicine.
Except for the fact that John and Mary might (probably would be, if his nearly non-existent dating life was anything to go by) be horrified and disgusted by the very thought of having their precious offspring being nurtured in a man's womb, Sherlock would suggest his solution immediately. Everyone except his close family had avoided him after they found out about his inner workings, but perhaps John and Mary would be different.
He had asked Dr. Clarke when he was 16 about the likely hood of having children. She said that it is possible for him to father his own offspring barring any complications that the rest of the male population face, like bad swimmers. In order for him to mother children though he would have to either use a surrogate or go off of his testosterone and start on some Oestrogen for a half year at least before attempting to conceive. After his last cocaine-morphine binge Mycroft took him back to Dr. Clarke, who was now a lot older than when he last saw her, and she said that despite his reckless behaviour there was no damage to his reproductive organs. The detective was immensely lucky in this regard, most people have their chances of parenting greatly reduced after taking as much drugs as he had.
There was no doubt in the detective's mind that he would do all of this for John. He knew how bad the body dysphoria would be, how much his body would change, how painful childbirth would be. He has survived being tortured and shot though, so it can't be any worse than that.
The only thing now stopping Sherlock from suggesting himself as the surrogate and/or egg donor, is the fear of John leaving him. His mother once said to him that a true friend wouldn't care that he has an ovary or two as well as his 'boy parts' as she had called them then. Sherlock knew that John would die for him, the Moriarty encounter at the pool had taught him that. If John was willing to kill and die for him, stay his friend even after the drugs and the faked suicide and countless other incidences, then why on earth would he leave him now?