After weeks of feeling sick and her belly growing, she finally decides to see the doctor. Only to have the best news and the worst news at the same time.

She's pregnant. 

After leaving the clinic, in a hast, she runs to her sister's room. Bursting through the door. Her sister, Princess Luna, jolts awake. "By the moon Celestia! We are trying to sleep the day away!" Luna exclaims. 
"Sister! I must tell you something!" 

Celestia explains everything to the tired Princess as they walk to the throne room. Once they reach the throne room, Luna asks the guards to leave. They do so. Luna explodes at her sister. "DO THY HAVE ANY IDEA HOW BAD THIS IT?! IF EQUESTRIA FINDS OUT, YOU WILL BE PUT OUT OF ROLE!!!" 
With tears in her eyes, she takes a scroll and quill and begins to write with her teeth grit, as her younger sister yells at her. 

Dear Princess Twilight and Flash Sentry,

I need your help before it’s too late. Something has happened to me and I need your help. Do not worry, I am in no danger, but your help is needed. Aid me in this, won’t you?
I will visit you in PonyVille later today. No guards, only me, no pony must know until I give the announcement.
Aid me Twilight Sparkle, you are my only hope.

Your Teacher and Princess,
Princess Celestia

And with that, the scroll is sent. Her sister's rant is over and a crowd of ponies are at the main door. Celestia and Luna look over. 

"My little ponies," the sun goddess speaks, "everything will be explained soon. do not worry for your Princess. The ponies scatter back to their work. The Princess sighs. "What am i going to do, sister?" she asks, hanging her head.