Under the cover of darkness
The moon peeked over the horizon, its sliver rays penetrating the inky darkness. It was a full moon, which meant visibility was higher. This wasn't good for the mare who trotted hastily, but silently through the city. No pony could find out what she was doing. Nopony. Not even her elder sister, whom she trusted with her life. If the news got out... Oh the rumors that would fly!
The normal hum of the city was gone, only a few ponies walked its streets. Hardly anywhere was open, and young foals would be soundly asleep.
Finally, she reached her destination, a small, closed, doctors surgery. She looked around the area casually, checking if anypony was around. When she was certain no pony was there, she silently trotted around the back, to a locked door, and knocked 5 times. After a little bit, a somepony opened the door.
"Princess! You're perfectly on time. You weren't followed... Were you?" The stallion looked fearfully around.
"No, I was not. Besides, Doctor Tart, you can call me Luna. After all this, we are most certainly friends."
"Yes, you are right Luna, you better get inside, before any pegasi guards notice us, and assume the worst." Golden Tart beckoned Luna inside, and quickly shut and locked the door. "And Luna, you can just call me Tart, no need to add the doctor part." He fidgeted with his glasses a little, before trotting off to another part of the surgery.
"Tart, I assume its another check? I'll make sure the security footage gets deleted." A small mare said, and smiled as she trotted past
As Luna came up to the ultrasound room, Tart stopped her.
"Be aware, you are going to have to tell them at some point. Things like this don't stay secret forever." Tart looked carefully at the mare, waiting for a response.
"I know. I shall tell them when the right time comes along." Luna replied, her eyes on the ground.
"Make sure the right time isn't to late. The earlier you tell them, the better." After making sure she understood him, he trotted into the room, and prepared everything. "Alright, just lie down. We'll see how the little ones doing." Tart gave a kind smile, began the ultrasound, scanning Luna's womb. The foal showed up on the screen, and with it, a fair amount of surprise from princess Luna in the room.
"Is... Is it an alicorn?" Luna's eyes opened wide, and she continued to stare at the picture.
"Yes...And its a filly," he squinted at the picture, and swiftly added "and is doing perfectly well, a young, healthy baby!"
"You aren't even a little surprised its an alicorn?"
'Well...No. After Flurry Heart, I was kind of expecting it."
"..."
"Well, that's it for this session, You should return to the castle now, and begin thinking of a name for the little princess!"
"...Yes, I will."
Luna left the surgery, put her cloak back on, and checked the skies. Once it was all clear, she flew high into the night sky, above the cloud layer, above where the guards were patrolling the skies. She flew for a bit, and landed on her balcony. If anypony had seen her land, they'd assume the princess of the night had just been for a quick flight.
"How will I explain this..." She sighed, and retreated to her bed.