Are these storylines turn ons for you:

Moms carrying high order multiples (quads+) unrealistically close to term, or even going overdue
Moms vaginally delivering/nursing high order multiples 
Multiple pregnancy that strains credulity (10+)

I’m down for the 1st 2, the last not so much

One of the things I enjoy about storytelling is you can do anything you want and are not bound by the limitations that exist in real life. When it comes to pregnancy and birth the female body can only do so much and in the case of multiples, it usually means they will be delivered via c-section. However, in a story, women can carry as many babies as the writer wants and birth them all vaginally which is the method I prefer. I'm not a fan of c-section births. A pregnant woman carrying more than one baby is a huge turn on for me mostly because of the massive belly size twins, triplets, and quads produce. A woman carrying more than one baby in her womb is not just pregnant, she is extremely pregnant which I find to be hot af.

Overdue multiple pregnancies are very arousing. In fact, I like to call the condition of being overdue "birth constipation".

Fictional pregnancies that have 10+ babies are okay and can be quite entertaining to read about especially if the proper detail is given describing how the massive load is affecting the mother's body.

Another story element I enjoy is heavy babies weighing 10 pounds or more that have grown so big each head provides a good test of the vagina's elasticity during birth.

GREAT REPLY @LTKNT101 ! Like I said, realistic multiples are AWESOME story elements and I totally agree about vaginally delivery of big babies! Love your term “birth constipation”.

I mostly, but not always, prefer realistic pregnancies - singletons or twins. Realistically, high order multiples are very high risk and the woman is too uncomfortable for sex. I mostly confine myself to situations that I or my readers might actually get to experience. You can still play around at the end of the bell curve. Some women DO get very big, you know, > 50" waistline. Some women DO develop enormous tits. Some women DO stay horny until they deliver. You can have a lot of fun within the range of normal. A woman is going to have ten babies weighing ten pounds each? Great! Let her have five twinner pregnancies, get bigger each time and stay horny throughout! Oh, yeah...

Now, having said that, I like playing around with other elements, too:
I wrote a story about a continuously pregnant surrogate. Every two weeks, she bears a big, healthy baby and gets implanted with another fertilized embryo. She's always pregnant with eighteen babies at two week intervals of development.
I wrote a series of stories about a woman who accidentally gets pregnant while carrying hundreds of donor eggs. Her doctors 'release' the embryos five at a time, so she's constantly pregnant with quints.
I wrote a story about a guy whose GF is one of a set of identical triplets. They are all physically and emotionally supercharged for pregnancy. They conceive easily, get very big, and recover completely after birth. His problem is how to keep their sexual appetites satisfied.
I wrote a story about an M/F team of cops where she gets instantly pregnant to complete an undercover assignment. This was a comedy where she got to thwart a sexist boss while getting tons of pregnant sex.

Does any of that sound interesting?