my pregnancy: 5 weeks

How your baby's growing:
Deep in your uterus your embryo is growing at a furious pace. At this point, he's about the size of a sesame seed, and he looks more like a tiny tadpole than a human. He's now made up of three layers — the ectoderm, the mesoderm, and the endoderm — which will later form all of his organs and tissues.

The neural tube — from which your baby's brain, spinal cord, nerves, and backbone will sprout — is starting to develop in the top layer, called the ectoderm. This layer will also give rise to his skin, hair, nails, mammary and sweat glands, and tooth enamel.

His heart and circulatory system begin to form in the middle layer, or mesoderm. (This week, in fact, his tiny heart begins to divide into chambers and beat and pump blood.) The mesoderm will also form your baby's muscles, cartilage, bone, and subcutaneous (under skin) tissue.

The third layer, or endoderm, will house his lungs, intestines, and rudimentary urinary system, as well as his thyroid, liver, and pancreas. In the meantime, the primitive placenta and umbilical cord, which deliver nourishment and oxygen to your baby, are already on the job.

See what's going on in your uterus this week.

Note: Every baby develops a little differently — even in the womb. Our information is designed to give you a general idea of your baby's development.

How your life's changing:
You may notice some pregnancy-related discomforts already. Many women report sore breasts, fatigue, and frequent urination starting in the early weeks. You may also have nausea, though it's more likely to show up in the coming weeks.

The outside world won't see any sign of the dramatic developments taking place inside you — except that you're turning down that glass of wine with dinner, perhaps. It's important to avoid alcohol throughout your pregnancy since no one knows exactly how much — or how little — alcohol can harm a developing baby.

You'll also want to continue or start an exercise routine. Exercise helps you develop the strength and endurance you'll need to manage the extra weight you'll be carrying. It may help prevent some of the aches and pains of pregnancy, and many women find that it's a great stress-reducer. Exercise can also help you get ready for the physical rigors of labor.

Finally, it's easier to bounce back after you give birth if you've continued some form of exercise throughout pregnancy. Choose a safe, moderately vigorous activity you enjoy. Walking and swimming are fine choices for pregnant women.

Dads, there are plenty of ways to participate in your partner's pregnancy — even this early in the game. Check out these great tips on how to get involved.

my pregnancy: 4 weeks

How your baby's growing:
This week marks the beginning of the embryonic period. From now until 10 weeks, all of your baby's organs will begin to develop and some will even begin to function. As a result, this is the time when she'll be most vulnerable to anything that might interfere with her development.

Right now your baby is an embryo the size of a poppy seed, consisting of two layers: the epiblast and the hypoblast, from which all of her organs and body parts will develop.

The primitive placenta is also made up of two layers at this point. Its cells are tunneling into the lining of your uterus, creating spaces for your blood to flow so that the developed placenta will be able to provide nutrients and oxygen to your growing baby when it starts to function at the end of this week.

Also present now are the amniotic sac, which will house your baby; the amniotic fluid, which will cushion her as she grows; and the yolk sac, which produces your baby's red blood cells and helps deliver nutrients to her until the placenta has developed and is ready to take over this duty.

See what's going on in your uterus this week. (Or see what fraternal twins look like in the womb this week.)

Note: Every baby develops a little differently — even in the womb. Our information is designed to give you a general idea of your baby's development.


How your life's changing:
Sometime this week, you may be able to find out whether you're pregnant. For the most accurate results, wait until the end of the week to take a home pregnancy test. (You can try one now if you like, but you're more likely to get a correct result a week past your expected period.)

If the test is positive, call your practitioner's office and schedule your first prenatal appointment. Most practitioners won't see you until you're about eight weeks along, unless you have a medical condition, had problems with a previous pregnancy, or are having symptoms that need to be checked out.

If you're taking any medications — prescription or over-the-counter — ask now whether it's safe to keep taking them. And be sure to alert your caregiver to any other issues of concern.

You should already be taking a multivitamin that contains at least 400 micrograms (mcg) of folic acid. Once you're pregnant, you'll need a bit more — 600 mcg a day — so switch to a prenatal vitamin if you haven't already.

The next six weeks are critical to your baby's development. The rudimentary versions of the placenta and umbilical cord, which deliver nourishment and oxygen to your baby, are already functioning. Through the placenta, your baby is exposed to what you take into your body, so make sure it's good for both of you.

If your home pregnancy test is negative, take another at five weeks if you still haven't gotten your period. Many urine tests are not sensitive enough to detect a pregnancy at four weeks.

If you've been trying to conceive with no success for a year or more (or for six months if you're over 35), talk to your healthcare provider about a workup exam for you and your partner to spot possible fertility problems. While the results may be upsetting, finding out about a problem sooner rather than later will get you started on the road to treatment — and to your ultimate goal: having a baby.