All About the First Trimester For most women, the first 12 or so
weeks of pregnancy are the most consuming because everything is
all so new, so exciting, even overwhelming. To satisfy the
little voice inside your head that keeps asking questions,
here's a primer. Keep it handy. X and Y chromosomes The sperm
determines the baby’s sex. Here’s how it works: The egg and
sperm each contribute one chromosome. The egg always carries an
X; the sperm, either an X or a Y. If the fertilizing sperm
contains an X chromosome, you will have a girl. If it contains a
Y, you’re having a boy. The fertilized egg, also known as a
zygote, is the size of an apple seed when you can confirm that
you’re pregnant—about two weeks after conception. By week five,
it’s known as an embryo, and the placenta and umbilical cord are
functioning. At eight or nine weeks, it’s officially a fetus and
all its organs have been formed. By the end of the first
trimester, it’ll be almost 3 inches long and the face will look
recognizably human. No wonder