This is not accurate on pregnancy, I just had to change some things about pregnancy to make the story plot make sense.

Marionettes Point of View
I woke up with a strange feeling in my stomach. I stumbled to the bathroom and threw up in the toilet. Why was I throwing up? Did I get food poisoning? After I felt less nauseous, I was about to put my hair up, but after thinking it, decided to leave it down, so no one else would question the mark on my neck. I changed into my usual clothes, and went to school.
I made it there just in time to see Jessica. "Hi!" She said happily when she saw me.
"Hi, Jessica!" I replied, walking up next to her. "Where's Alya?" I asked.
"I don't know, she's not here yet." Was the answer I got. I turned around to see Adrien, who had apparently decided to join our conversation. He looked at Jessica. "I don't think that we've been properly introduced, I'm Adrien."
"You look familiar," Jessica said, "is there anywhere that I could have seen you before?"
"Well, I am a model, so you probably have seen me in a magazine or something."
"Oh, I just remembered where I've seen you before." Jessica said, nudging me, and I knew that she was talking about the pictures on my wall. "In a magazine." She said, letting me breath once again.
He smiled. I loved that smile. It was as if it was the sun itself, it certainly warmed me up.
"Everything all right?" Adrien asked me, his cheeks pink. I realized that I had been staring.
"Ummm... y-yeah, it, it's just that-" I was cut off, or saved, by Alya.
"Hey Marionette and Jessica!" She said, slinging her arm around my shoulder. "Hey Adrien." She said while using her hand to squeeze my shoulder.
"Hi Alya." Adrien said.
The bell rang.
Alya let her arm slip from my shoulder as she left to converse with Niño and Adrien. Jessica was suddenly at my side.
"Mind if I come over to your house later?" She asked.
"Yeah, how about at lunch. You and Alya could come over for some croissants." I answered, a smile forming on my mouth.
"No, I mean just me and you, there's something important I need to ask you."
"Okay." I said, confused by her behavior. What did she need to ask? Was it about Adrien? I hoped it wasn't about him. I didn't want to undergo more humiliation when I'm with him than I already do, tripping over almost everything and not being able to form a sentence around him.
Jessica nodded and went to her locker as I went to mine.
I went into the classroom and sat in my seat just as Alya slid in next to me.
One extremely boring class period later, the bell rang, and I gratefully started walking home to the Dupain-Cheng bakery. When I got there, I grabbed a few cookies and went upstairs to my room. Tikki flew out of my purse as soon as I opened it.
"I wonder what Jessica wanted to talk about, she sounded serious." She said to me in her high-pitched voice.
"Yeah, it's been bugging me." I said, curiosity building up in me. I held up the cookies, and Tikki gratefully took one and started munching on it.
"Marionette, your friends here!" My mother called up to me.
"Thanks Mom!" I yelled back and gestured for Tikki to hide. She flew behind a pile of books on my desk just as my trapdoor opened to reveal Jessica. She had a smile on her face.
"Your mom is so nice!" She said, biting into a croissant that she had picked up from the bakery.
"Yeah." I agreed, "Anyways, what did you want to ask me?"
The smile vanished from her face as she came up and sat on my chaise. "Why were you early to school today, Alya tells me that your always sooo late."
I decided that I should be truthful with Jessica, as long as it didn't have anything to do with me being Ladybug. "I was woken up quite early with a wave of nausea." I said.
Jessicas face grew graver as she sling her backpack off of her shoulder and unzipped the zipper. "I hoped that I brought this for nothing." Jessica said, pulling out a cardboard box that was about the size of my diary box.
"What is this?" I asked.
"Something that could change your future." Jessica said, making me even more confused.
I opened the box and gasped at what I saw. It was a

...

Pregnancy Test.
"Y-you don't think that I could be-" I couldn't finish.
"If I didn't have a concern, then I wouldn't have brought it."
I slowly stood up with the box and went to the bathroom to try it out.

...

Positive.
That's what the sign said.
It was official.
I, Marionette Dupain-Cheng was pregnant with Chat Noirs baby.

Adrien's Point of View
This is after school
Why did I do that! I jumped in uninvited on Marionettes conversation with the new girl, Jessica. Marionette probably hates me now! She didn't come back to school after lunch! Wait, when did I start to obsess over Marionette like this? Was I, in love with her? No, I liked Ladybug, right? Why did my emotions have to confuse me so much? I mean, sure, Marionette and I did have our crazy night together, but I was the confident Chat Noir, and that was accidental, I didn't fall for her, did I? I did kiss her when I wasn't under the influence of the gas, and I liked it, I'm pretty sure that she did too, but I liked Ladybug.
"You've been sitting there for an hour, Adrien, what is going on?" Plagg asked me.
"I think that I may have fallen for Marionette, but I feel like I'm betraying Ladybug. My emotions are all mixed up!" I grumbled through my pillow, as I was facedown on my bed.
"Sounds like you need to visit Marionette to see if you really do love her." Plagg said.
"Great idea!" I said, sitting up. "Plagg, claws out!"
"Wait, I meant as Adrien!" Plagg yelled as he was sucked into my ring. I ignored him, I'd much rather face Marionette as Chat Noir because I needed his confidence. She would also feel the same awkwardness around me that I felt around her, since she slept with Chat Noir, not Adrien. I leaped out of my window and went off to my favorite bakery.