Your Developing Baby: Week 4

What's going on with your baby in pregnancy week four? Find out all about important pregnancy milestones and exciting fetal development specific to this week of pregnancy!

Week 4 American Institute of Ultrasound in Medicine -

What you can't see on this picture are the changes going on in your bloodstream. Within the first few days of your baby-to-be's development, your body begins to produce and circulate human chorionic gonadotropin (hCG), the so-called "pregnancy hormone." This is the same hormone that triggers a positive reading on your pregnancy test. In fact, until the hCG levels reach 1,000-2,000 mIU/ml, indicating that there's a growing gestational sac, the sonographer (the ultrasound technician) will most likely not be able to pick up an image during an ultrasound exam.

Over the next few days, this sac will grow at a rate of 1 mm daily. As it develops, the levels of hCG will grow proportionately, too. The hCG levels will double every few days, and this increase is thought to be the reason many women feel nauseous. These hormones flood your entire body -- not just your uterus.

Because hCG levels are directly related to the growth of the gestational sac, your health care provider will be taking a close look at the hCG levels in your bloodstream. Too high or too low of hCG levels might mean there is a problem with the pregnancy.

Keep in mind that ultrasounds are usually not performed this early in a pregnancy -- you're getting an exclusive sneak peek here! If your health care provider does request an ultrasound, she's most likely confirming your pregnancy and looking at the placement of the gestational sac. That small circle you see in the center of the image is exactly where it should be, protected deep within the uterus.

    Terms to Know

    Sonographer: The person who performs your ultrasound examination. These specialists receive advanced training at reading sonograms.

    Sonogram: An image produced by an ultrasound examination. Most often performed by a sonographer; sometimes performed by your health care provider.

    Ectopic pregnancy: A fertilized egg growing outside the uterus. Most often ectopic pregnancies develop in the Fallopian tube, where the egg travels from the ovary to the uterus. This condition poses a serious health risk to the mother, requiring the health care provider to remove the fertilized egg and end the pregnancy.

    Important Information About Your Pregnancy

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    Images courtesy of the American Institute of Ultrasound in Medicine (