Your pregnancy week by week: Weeks 1-4


If you are newly pregnant, or trying to conceive, you have many questions about what to expect. How will your body change? What's happening inside you?

We can guide you, week by week, through the nine months of pregnancy. Each week offers information about your body and baby's, as well as invaluable tips. Let's start with a peek inside the womb.

Weeks 1 and 2
Baby: Your baby is still just a glimmer in your eye. Although it's confusing to think about a pregnancy starting before your child is even conceived, doctors calculate your due date from the beginning of your last menstrual cycle, because it's difficult to know exactly when conception occurred.

Mom-to-be: At the beginning of your period, about 20 eggs called ova occupy fluid-filled sacs called follicles. If you typically have your period every 28 days, then about 14 days later, you ovulate: One of these follicles releases an egg, and it travels down your fallopian tube, where it awaits fertilization. This time -- 14 days after your period started and for a day or so longer -- is when you're the most fertile, so if you want to get pregnant, this is the best time to try! Once the egg is fertilized, it moves into the uterus.

Don't be disappointed if you don't get pregnant the first time. Each month, women have a 25% chance of getting pregnant, so you may need some time.

Tip for the Week: Make sure you've scheduled a preconception visit with your ob-gyn to determine risks of genetic diseases, environmental hazards, and lifestyle changes necessary to ensure a healthy pregnancy and baby. Most important, make sure you've started taking 0.4 milligrams, or 400 micrograms, of folic acid a day. Folic acid taken a few months before conception has been shown to dramatically reduce such neural tube defects as spina bifida.

Week 3
Baby: Congratulations! If your egg and your partner's sperm have joined successfully, your embryo is really there, although it's very small -- about the size of the head of a pin. It doesn't look or resemble a fetus or baby; it's just a group of about 100 cells multiplying and growing rapidly. The outer layer of cells will become the placenta, and the inner layer will become the embryo.

Mom-to-be: You won't notice any changes in your body at this point. Remember, you haven't even missed your period yet.

Tip for the Week: Can't wait to find out? Take a home pregnancy test. They're about as reliable as a urine test or blood test done in the doctor's office – and their results are immediate. To ensure accuracy, read the directions carefully and make sure all the supplies you are using are clean.

Week 4
: Now that your egg is fertilized, it burrows into the lining of your uterus. This is called implantation.

Mom-to-be: You're probably expecting your period this week, and if it doesn't occur it might be one of the first signs that you're pregnant. You may also notice light spotting as the embryo implants itself in your uterus. You might not feel any different yet, but the amniotic cavity, which will be filled with fluid, and the placenta, which will bring oxygen and nutrients to nourish your baby, are forming in your uterus.

Tip for the Week: Try to eat healthfully, which means choosing a variety of foods from recommended food groups and drinking at least six to eight 8-ounce glasses of water a day. But you don't really need to "eat for two;" you only need an extra 300 calories per day during pregnancy. And don't worry if your food intake drops in the beginning because of morning sickness. If you've been eating right already, your baby will get what it needs.

What's happening inside you?
The fertilized egg grows and, a water-tight sac forms around gradually filling with fluid. This is called the amniotic sac, and it helps cushion the growing embryo.

The placenta also develops. It is a round, flat organ that transfers nutrients from the mother to the baby, and transfers baby's wastes.

A primitive face takes form with large dark circles for eyes. The mouth, lower jaw, and throat are developing. Blood cells are taking shape, and circulation will begin.

By the end of the first month, your baby is about 1/4 inch long - smaller than a grain of rice!