Even though we already knew a lot of Tori Roloff's delivery details when it came to baby Lilah, it's another thing to get to see the pregnancy play out.

In this sneak peek, Tori and Zach go for a doctor's visit ... and learn that their baby girl will be a little person.

In this sneak peek of Tuesday night's new Little People, Big World, Tori and Zach already know that they're expecting a baby girl.

Together, they visit Northwest Women's Clinic for another important prenatal check-up.

Tori is four months pregnant in this scene, and she is scheduled for an anatomy scan.

And, of course, they brought little Jackson with them to include him in the process.

Tori makes an audible noise as the cold ultrasound gel is applied to her pregnant belly.

She and Zach watch the monitor, as you can see in the video that we have included.

Meanwhile, Jackson gets a little distracted.

Doctor's visits can seem to take a long time when you're just a few years old.

At this point, Jackson's "baby sister" if four-and-a-half centimeters long -- which is less than two inches.

Lilah weighs one pound and nine ounces at this stage.

"I think that it's just important that our baby is healthy," Tori remarks.

Meanwhile, Jackson is getting super excited - more about his mother's pregnant belly than about the ultrasound on the television.

Tori comments that, in the early stages of pregnancy, it can be "nerve-wracking" to wonder if her child is okay.

Zach remarks on how grateful he is that Jackson has suffered no health issues.

"He is very blessed," Tori agrees.

She continues: "I hope that carries over when we have babygirl, whether she is average height or a dwarf."

Speaking of which, Tori and Zach sit down with the doctor to find out a little more about Lilah.

"Everything looked normal on the ultrasound," the doctor informs them both. "But ..."

The dramatic pause here, crafted by editing and not by the doctor herself, is an absurd bit of reality TV shenanigans.

"Her head is larger," the doctor informs the expecting parents, "and most of the longbones are about two weeks behind."

Tori and Zach already understand what this means, but the doctor of course spells it out.

"Everything is measuring right on track for achondroplasia," the doctor notes.

Achondroplasia is the type of dwarfism that Jackson, Zach, and Zach's mother Amy all have.

Unlike his mother or son, Zach has had numerous medical complications, like his father -- notably, Matt has diastrophic dysplasia.

Obviously, Tori and Zach are totally prepared to be parents to a second little person, but Zach admits that "It's a lot to process."

Any time that parents know that their child will have disabilities, they are conscious of how different their lives will be.

Still, they are hopeful that Lilah's achondroplasia will be free of complications, like Jackson's has been so far in his young life.

This sneak peek is so sweet and honest - we can't wait to see the full episode on Tuesday.