10. For trans kids and teens, if you go from taking puberty-suppressing medication directly to hormone replacement therapy, that can render you infertile down the line.

First, a few words about a typical scenario that a trans kid might face:

Typically a child who is gender-nonconforming will begin talking about it at age three or four, Finlayson says. "They start saying it very young, and they're very persistent and insistent, and they're very upset by the idea that they're in the wrong body," she says.

When a gender non-conforming child reaches puberty, they may develop gender dysphoria — this is when "the individual becomes very upset and traumatized by the changes they're seeing in their body," Finlayson says. Not all gender-nonconforming adolescents will experience dysphoria, but some might. Finlayson says that the Endocrine Society guidelines for care recommend that the child take puberty-suppressing medications at this stage.

"[Puberty-suppressing medication] is a medication that is generally speaking very safe, and can be used to just pause puberty," Finlayson says. "If a year later they think they want to go through with their natural puberty, that's fine — it's reversible, and we think it doesn't have any long-term harm." The reason doctors recommend the puberty-suppressing medication at this stage is because it can help kids take some more time to figure out what they want, without the potential trauma or stress of being in a rapidly changing body that is becoming something even farther from what they identify with. But another important reason is because it can potentially help them avoid future surgical operations down the line — thanks to puberty-suppressing medication, trans boys will never develop breasts, for example, which would make a future double mastectomy unnecessary.

After a few years of taking puberty-suppressing medication, with the help of a mental health team, the teenager may then choose to start using hormone replacement medication if they decide that's the right path for them, Finlayson says.

Here's where the fertility issues come in:

"When an individual goes through puberty, the germ cells — what becomes eggs or sperm — mature," Finlayson says. "You have to have puberty for those cells to mature. So if we prevent puberty from occurring, the germ cells in those gonads, whether they're ovaries or testicles, are not going to mature. So in that situation, those individuals who have never gone through a natural puberty in their body — they're not going to have germ cells to use."

In other words: If a trans teen goes directly from using puberty-suppressing medication to hormone-replacement medications, they have not ever undergone puberty, and it may render them infertile in the future.