This article was originally featured by What to Expect [1], a pregnancy and parenting brand helping every parent know what to expect, every step of the way.

"Are you comfortable?" the ultrasound tech asked as she prepped my belly for a routine scan. I was eight months pregnant [2] with my fourth child who thought my bladder was a trampoline and communicated solely through heartburn and cravings for frozen lemonade at midnight. Oh, and it was July in the Midwest; the temperature had been above 90 for weeks with high humidity. I was many things at that moment — hot, cranky, tired, bloated [3] — but comfortable certainly wasn't one of them. But before I could even answer with my litany of totally-normal-yet-annoying pregnancy complaints, the tech gasped.

"There's a . . . something in your ovary," she said, peering closely at the screen. "I think it's a tooth?"

"A what?" I yelled as I tried to sit up. (No easy feat when you're that pregnant, by the way.)

She zoomed in on the bright white dot. It did kind of look like a tooth. In my right ovary.

She called in my doctor who confirmed that, yes, indeed, it was likely a tooth and there was probably a bunch of other random stuff in my ovary with it. I had a dermoid cyst.

A dermoid cyst is technically a teratoma tumor; teratoma is Greek for "monster" — a descriptor you'll soon understand. It is a sac-like growth that can contain tissues including hair, fluid, fat, skin, bone, thyroid, neural fluid, teeth, and in rare cases eyeballs, and while they sound freaky, they're actually not that unusual, says Kelly Kasper, M.D., an OB/GYN at Indiana University Health.

Dermoid cysts form from a totipotential germ cell, an egg that's still inside the ovary. These embryonic cells are used to make all the tissues for a baby but sometimes they go rogue and start randomly making tissue on their own, she explains. No one is exactly sure why they form, but they're one of the most common ovarian growths in women of childbearing years, making up 15 to 20 percent of all growths on the ovaries according to the Mayo Clinic [4].

Since they typically don't show symptoms, they're most often discovered during pregnancy or when trying to get pregnant, says Sinem Karipcin, M.D., a reproductive endocrinologist at Conceptions Florida, a Miami-based fertility centre. Pregnancy doesn't cause them (in fact, some may be present since birth), but it is the time when people are most likely to be poking around your ovaries to find them. They're typically very slow-growing but they can get quite large, with some reaching 17 inches in diameter, or the size of a large watermelon. They don't usually pose a problem to the pregnancy, she says, adding that despite the word "tumor," they're almost never cancerous. (Studies have found [5] that complications from dermoid cysts are extremely rare.)

The real risk from a dermoid cyst is the possibility of ovarian "torsion," meaning that they cause the ovary to twist and cut off blood supply, Kasper says. You'll likely know if this is happening to you as you'll feel a sharp pain in your side. Again, complications are extremely rare, but if it does happen, a torsion requires immediate surgery, she adds.

Since my dermoid was relatively small (about the size of a golf ball) and I didn't have any pain, it was decided they'd just leave it alone for the remainder of my pregnancy and then I'd have surgery to remove it after my baby was born.

I was okay with this plan until I really started thinking about it. Just because they're not dangerous doesn't mean they're not super creepy. It was weird walking around knowing that I had a glob filled with hair and fat and a random tooth floating around in my ovary. It almost felt like my body had attempted to make a twin and just ran out of steam. I wondered if my baby could feel it. I wondered if I'd be able to feel it once my abdomen had reverted to my sole ownership. I wondered if I could keep the tooth to show to my kid once he got old enough to appreciate all the things I'd done for him. (Which would be . . . when exactly?)

My delivery date came and everything went smoothly. I screamed a lot. The father in the next room came in to ask me to keep it down because I was scaring his wife. My mom told him to tell his wife to buck up. And then I birthed a beautiful baby boy who was not holding a tiny tooth in his tiny hand, like I'd dreamed. He was 10 pounds, 12 ounces, though, which explains all the screaming.

Four months later, I had laproscopic surgery to remove the dermoid tumor. When I woke up I asked the doctor if I could see it. She said no, she'd thrown it away immediately.

"It was that bad?" I asked.

"So gross," she answered. "And the tooth didn't even look like a real tooth."

I sighed. "I spent nine months growing it and I don't even get to hold it?"

"Well," she added, as she turned to walk out the door, "with this type of cyst, there's a 50/50 chance it will grow back."

Now every time I get my annual check-up, I ask them to do an ultrasound and look for a tooth. So far, so good!

Related:

• Buying For Baby: A Guide to Big-Ticket Nursery Items [6]
• When to Tell People You're Pregnant [7]
• Space-Saving Tips For the Nursery [8]