4 Weeks Pregnant

This week, the blastocyst continues to implant more deeply into the uterine lining. Most of the time, the egg implants at the top back wall of the uterus. The hollow blastocyst flattens into two layers. The yolk sac will nourish the embryo until the placenta takes over. The amnion will grow to envelop the embryo in a protective sac.

As the fertilized egg implants in the wall of your uterus, you may have slight cramping or spotting. By the end of this week, you will have your first missed period — and perhaps notice other early signs of pregnancy.

Early pregnancy is an important time to protect an unborn baby from exposures to chemicals. Check the labels on the products in your home or workplace. In general, you'll want to steer clear of:

• Pesticides and herbicides — chemicals to keep away or kill bugs, rodents, or plants
• Paints, paint thinners, and varnish removers
• Oven and carpet cleaners

For specific questions about chemicals, medication, or other substances, call Poison Control toll-free: 1-800-222-1222.