Credit: ABC

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Grey's Anatomy Season 9, Episode 12: "Walking on a Dream" may have a cheerful title, but the official synopsis makes the episode sound anything but fun for Meredith (Ellen Pompeo). In fact, "while battling pregnancy hormones, an overly-emotional Meredith is confronted with her worst fear." Oh no!

As soon as we read that we went into speculation mode. What is Mer's "worst fear" at this point, and how is she confronted with it? Here are our top four theories.

1. Alzheimer's. Her potential Alzheimer's has always weighed heavily on Mer, but in the past she's refrained from finding out if she has the gene. However, now that she has a biological baby on the way, maybe she'll finally "confront" the truth. If this is the way the episode goes, we hope Mer ends up receiving good news.

2. Pregnancy complications. One of Mer's more recent worries is losing her baby due to her hostile uterus. While we doubt she'll miscarry, it's possible she'll run into frightening complications this episode.

3. Something bad happening to Zola. Isn't every parent’s worst fear something bad happening to their kid? Maybe Zola gets sick again. It's not that unlikely. After all, she only came to the States in the first place because she was ill.

4. Becoming her mother. A more nebulous fear for Mer has always been becoming her mother — cold, harsh, and distant. Maybe her pregnancy hormones combined with her new "Medusa" nickname will send her into a downward spiral of self doubt.

What do you think? Share your theories in the comments below.

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Catch the next new episode of Grey’s Anatomy on Thursday, January 17, 2013, at 9 p.m. ET/PT on ABC.