Well, it could be about the challenges Clary faces during childbirth, like her fear and the support she gets from her friends. Maybe her partner is by her side, holding her hand through the pain.
Obviously, Clary herself is the most important character as she's the one giving birth. Her partner would also be crucial, providing support and sharing the joy of the new arrival.
One possible scenario could be that Clary is in a situation where she has no one around due to some unforeseen circumstances like being stranded in an isolated place. Another could be that she chooses to be alone because she doesn't want others to see her in a vulnerable state during childbirth.
Maybe Simon. If the fanfic takes an alternate path where Clary and Simon end up in a romantic relationship, he could be the father. However, he might be away or unable to be with her when she gives birth.
Obviously, Clary herself is central. Then there's Jace, her love interest. He would be very involved, probably being there for her throughout the pregnancy and during the birth. Simon might also be there. As Clary's best friend, he would offer his support in his own way, perhaps with some comical moments to lighten the mood.
One popular storyline could be Clary's struggle during childbirth. Maybe there are complications, and the other characters in the 'Shadowhunters' world have to come together to support her. For example, Jace could be by her side, freaking out but trying to be strong for her.
I'm not sure specifically as I haven't read that particular fanfic. It could be about Betty's experience during childbirth, perhaps the emotions she goes through, the people around her at that time, and how it changes her life.
Obviously, Ana herself would be the central character. Her partner could be an important character too, being there for her during the pregnancy and birth. Maybe her mother or a close female friend who offers advice and support.
The fanfic might focus on the actual birth. It could describe the setting, whether it's in a hospital or at home. And also the people around her during the birth, such as a midwife or her partner. There could be some tense moments and then the joy of the new life arriving.
It could be a mortal man who somehow managed to catch Artemis's eye. Maybe he was a great hunter like her, and their brief encounter led to the pregnancy.