Taking shape: What to expect trimester by trimester (Part 1)

In 40 weeks your body undergoes some serious changes both inside and out.

Before you even see those two little blue lines, your body is busy building the perfect environment for your budding baby. So what exactly is going on? Here's a breakdown of what you can expect, trimester by trimester.

First trimester (1 to 13 weeks)

While you might not be able to tell you're pregnant by looking in the mirror, your body will begin to undergo subtle changes during the first three months that will serve as daily reminders of your mommy-to-be status. Your waistline may remain as svelte as it was pre-pregnancy (you'll probably only gain 2 to 5 pounds), but your first trimester will welcome growth in other areas: Your breasts and uterus are both expanding to accommodate your growing fetus. The weeks following conception can give way to a few less-than-fun side effects of pregnancy. Morning sickness (which, despite its title, doesn't only occur in the morning) can bring nausea and vomiting. On top of feeling icky, most moms also report being abnormally tired. You can blame these problems (along with some serious mood swings) on your fluctuating hormones. The combination of these crazy hormones, fatigue and tummy-upset could also lead to a decreased sex drive. Once your body settles in and gets used to the changes it's undertaking, these issues will likely dissipate.

Highlights: Morning sickness and mood swings

Your baby: The tiny embryo inside you is growing organs and tissues and will soon be recognizable as a human baby. His heart begins to beat, and his eyes, nose, ears and appendages start to form. He even has fingerprints!