5 weeks

Your BabyYour baby's microscopic heart begins to beat this week—although it won't be detectable with one of those cool Dopplers for a few weeks, so you'll have to wait a little longer to hear that satisfying "whoosh-whoosh" you're so anxious for. Here's what else is under construction:

With the beating of the heart, blood will begin to circulate throughout the body. Your baby's first organ system will be up and running!

The beginnings of the brain; the cardiovascular, nervous and reproductive systems; as well as all other major systems are under way.

Your baby's new digs—the amniotic sac and the placenta (aka the hotel and the restaurant)—are still forming at this point. (Maybe you should send a housewarming gift.)

All that high-speed development and your baby is only 2 millimeters long—about the size of a sesame seed (check one out next time you're chowing down on a bagel—you won't believe how tiny it is!).

Children are a gift from the LORD; they are a reward from him. Psalm 127:3

Coming July 17, 2011

Your Body
This is when it all begins.

Once Mini Me or He implants in your uterus and that placenta starts to grow, your heart starts beating more quickly. You might be putting in an extra 15 beats per minute (even when Taye Diggs isn't onscreen). Until your blood volume catches up to all that extra pumping (which it won't do for a number of weeks), you're likely to feel tired most of the time. Sounds like a good reason to schedule a siesta!

A lot of that extra blood is heading straight for your breasts, resulting in tenderness and the tendency for your nipples to show ... through your down jacket. (Another early pregnancy sign: Your cervix is softening and changing color. But if this is something you're able to notice on your own, we don't want to know about it.)

Your Baby
Your microscopic embryo is already hard at work this week creating the placenta, umbilical cord and the basics of his or her body.

The embryo is now made of three layers that will transform into the different parts of your baby's body. The endoderm, or inner layer, will become your baby's intestines, liver and lungs. The middle layer, or mesoderm, will become your baby's heart, sex organs, muscles, bones, and kidneys, and the ectoderm, or outermost layer, will develop into your baby's hair, skin, eyes, and nervous system. Believe it or not, your baby is already starting to look like a tiny little being (not necessarily a human being) complete with a head, a mouth opening and a primitive brain and heart.

By the end of this week, your baby measures about 1/25 inch long, about the size of a period (like the one at the end of this sentence, not the one you just missed).