All About Baby
The end of the first trimester marks an important step for your baby-to-be. All of her major body systems are in place. In her digestive system, her small intestine is no longer entwined with the umbilical cord, but instead is tucked neatly within the abdomen. Her nervous system continues to develop, and her brain's structure is fully formed. Many of her organs are starting to work on their own, too. For instance, her thyroid begins to secrete hormones. In your 13th week of pregnancy, she's no longer considered an embryo, but instead graduates into a fetus. She's already looking more and more like the baby you're probably imagining—she even has tiny fingernails.