Your Pregnancy: 3 Weeks

Your Pregnancy: 3 Weeks

How your baby's growing:What's going on in your womb now?

A lot. Your baby-in-the-making is just a tiny ball consisting of several hundred cells that are multiplying madly. Once the ball of cells (called a blastocyst) takes up residence in your uterus, the part of it that will develop into the placenta starts producing the pregnancy hormone hCG (human chorionic gonadotropin), which tells your ovaries to stop releasing eggs and triggers increased production of estrogen and progesterone (which keep your uterus from shedding its lining — and its tiny passenger — and stimulates placental growth). HCG is the hormone that turns a pregnancy test positive; by the end of this week, you may be able to take one and get a positive result! (If your test is negative and you still haven't gotten your period in two or three days, try again then.)

Quick Clicks Seventeen things you should do before you try to get pregnant Your likelihood of having twins or more Vaginal bleeding or spotting during pregnancy How smoking during pregnancy affects you and your baby Have you told others you're trying? Meanwhile, amniotic fluid is beginning to collect around your ball of cells in the cavity that will become the amniotic sac. This fluid will cushion your baby in the weeks and months ahead. Right now, your little blastocyst is receiving oxygen and nutrients (and discarding waste products) through a primitive circulation system made up of microscopic tunnels that connect your developing baby to the blood vessels in your uterine wall. The placenta won't be developed enough to take over this task until the end of next 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.

Your Pregnancy: 3 Weeks

Video Inside pregnancy: Fertilization An up-close, 3D animated look at the journey sperm take inside a woman's body and what happens when one sperm fertilizes a woman's egg.

How your life's changing:A momentous meeting has taken place inside you — a single sperm has broken through the tough outer membrane of your egg and fertilized it. Several days after conception, the fertilized egg burrowed into the lining of your uterus and started to grow. A baby is in the making! You probably don't know you're pregnant yet, but you may notice a little spotting by the end of this week. This so-called "implantation spotting" may be caused by the egg burrowing into the blood-rich uterine lining (a process that began last week at 6 days after fertilization), but no one knows for sure. In any case, the spotting is very light and only a minority of pregnant women experience it at all.

A baby-safe cocktail "I really missed my nightly glass of wine, so I invented a new ritual: ending my day with a blend of cranberry juice, seltzer, and a squeeze of lemon poured into a wine glass and enjoyed along with cheese-and-cracker hors d'oeuvres."

Surprising Facts: Early pregnancy symptomsSome women feel pregnant even before the test turns positive.

The earliest signs include:

Tender, swollen breasts Many women say the tenderness they feel is an exaggerated version of how their breasts feel before a period.Fatigue Feeling tired all of a sudden — no, make that exhausted? Increased levels of the hormone progesterone and the extra effort required to start making a baby can make you feel as if you've run a marathon when all you've done is put in a day at work.Frequent urination Shortly after you become pregnant, you may find yourself hurrying to the bathroom at an alarming frequency.Heightened sense of smell Many newly pregnant women find they're overwhelmed by gag-inducing smells early in pregnancy. This may be a side effect of rapidly increasing levels of estrogen in your system.Food aversions Food turn-offs are even more common than cravings during pregnancy. You may suddenly find that certain foods you used to enjoy are now completely repulsive to you.Nausea or vomiting Morning sickness usually doesn't start for a few weeks, but some women feel queasy earlier.Your basal body temperature stays high If you've been charting your temperature and it stays elevated for 18 days in a row, you're probably pregnant.Bleeding or spotting Some women notice a small amount of red spotting or pink or reddish brown staining around the time they should get their period. (If you have pain along with spotting or bleeding, call your caregiver immediately since this can be a sign of an ectopic pregnancy.)As tempting as it is, hold off on using a home pregnancy test. The vast majority don't work well until a week after you've missed your period, so using one now will only waste money and time.

This Week's Activity:

Buy a pregnancy test kit. Have a home pregnancy test on hand in case you don't get your period next week. Most home tests can accurately detect pregnancy in the week after your period is normally due — two weeks after you ovulate. Buy a kit that has multiple tests, so you can take it more than once. For best results, test first thing in the morning.

Next: Your Pregnancy: 4 Weeks