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.

Zygote
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 you’re tired!


Before You Get Pregnant

 A healthy pregnancy starts long before you test positive. Here’s a preconception checklist:
 

 

•  See your doctor several months before you want to conceive—and bring your partner. Doing so may help you prevent birth defects, pregnancy complications or prematurity, the March of Dimes reports.
   
•  Tell your doctor about any prescription or over-the-counter drugs or herbal remedies that you are taking.
   
•  Begin taking a prenatal vitamin with folic acid daily (see “V”).
   
•  Keep a calendar of your menstrual cycle. It may help you conceive sooner and estimate your due date more accurately. * Make sure your vaccinations, especially for chickenpox and rubella, are up to date.
   
•  Have any necessary dental work done: Gum disease has been linked to premature labor; and you’ll want to avoid X-rays when you’re pregnant.
   
•  Stop smoking (your partner should, too) and drinking alcohol.
   
•  Limit your intake of caffeinated beverages to just 24 ounces a day.
   
•  Get any chronic medical conditions, such as diabetes and hypertension, under control.
   
•  Have your thyroid checked. “Both hyper- and hypothyroidism can be associated with pregnancy loss,” says Dallas OB-GYN Susan Watts, M.D.
   
•  If you’re very over- or underweight, you may not ovulate normally; try for a healthier weight.