Welcome to Week 3! It might not feel like much of anything has changed so far—perhaps the only sign you’re pregnant at all is a positive pregnancy test.

But rest assured: amazing things are happening. Your baby is already developing and is likely implanted in your uterine wall, and your body has already begun to make subtle changes that will later blossom into full pregnancy.

Your Body 

your pregnancy week 3

At three weeks, many women have no idea they’re pregnant yet, in part because they haven’t missed any periods, and there are few symptoms of pregnancy. Others may have noticed they didn’t ovulate on time, or there might have been slight cramping or even spotting during fertilization. Sometimes tender breasts might be the only tip off that a woman is pregnant at this point.

Nevertheless, your actions can still affect your baby at this early stage. Many doctors recommend that women trying to get pregnant already act as if they are pregnant, which means taking prenatal vitamins, eating a healthy diet, getting plenty of sleep, and engaging in moderate exercise most days of the week.

It’s also a good idea to make sure you’re getting enough folic acid, which many pregnant women take as a dietary supplement. Folic acid supplementation before pregnancy and during early pregnancy helps prevent neural tube defects, which is a type of birth defect that can occur in a developing baby. The most common of these neural tube defects is spina bifida. The recommended daily intake of folic acid for most pregnant women is 400 mcg a day (this can be higher for certain high-risk women, such as those with a history of a seizure disorder). Certain medications, such as Phenobarbital, have been shown to affect folic acid metabolism, so let your doctor know if you are on this medication. Smoking reduces folic acid levels and should be avoided (for many other reasons, too).

If you suspect you’re pregnant and you haven’t already been under the care of a physician, start taking an over-the-counter prenatal vitamin with folic acid right away—don’t wait for your first visit or a prescription! By the time most women have their first visit, the critical window when that extra folic acid is needed has already passed, so it’s a good idea to start that vitamin ASAP.

When it comes to exercise, there’s no reason to stop or change your exercise routine—and if you don’t regularly exercise, now is a good time to get started. The majority of pregnant women in the United States get far too little exercise, which is a shame when we know how beneficial it is for mom and baby. Classes like yoga and Pilates are great for pregnant women as they increase flexibility and core strength. If you prefer to lift weights, it’s OK to continue weight lifting early in your pregnancy, but you will be restricted later on both in weight and how you position yourself. Keep in mind, however, that you are still pregnant, so it’s not a good idea to begin a strenuous new exercise program, start training for a marathon if you’ve never run before (as if you could run one later on anyway!), or dramatically increase your training.

Overall, exercise has been shown to have profound benefits for pregnant women, increasing their strength and flexibility and making both labor and recovery easier later on. The American Congress of Obstetricians and Gynecologists recommends that pregnant women get 30 minutes of exercise most days of the week.

Your Baby 


Heading into Week 3, your fetus is one week old (doctors refer to this as the “fetal age” and it will always be two weeks behind your pregnancy week). At this point, the fetus is tiny—less than one-hundredth of an inch long and invisible to the naked eye.

During a normal fertilization, the egg is fertilized in the fallopian tube, creating a ball of cells called a zygote. The zygote is a beehive of activity as the cells divide into blastomeres that join together to form a blastocyst. During the week after fertilization, the blastocyst travels down the fallopian tube toward the uterus, where it will burrow into the uterine wall.

By the time the blastocyst is firmly embedded in the uterine wall, many “decisions” have been made that will determine who your baby will be for the rest of his or her life. In fact, this happens at the moment of fertilization.

When an egg is fertilized, the genetic codes of the mother and father are mingled. A normal human has 46 chromosomes, which carry the unique genetic information that determines everything from hair color to your risk for heart disease later in life. This genetic code is “set” during fertilization, when a sperm carrying 23 chromosomes from the father mingles with the egg carrying 23 chromosomes from the mother.

Doctor Tip
“You might fall victim to common first-trimester symptoms like nausea and fatigue.”

See more doctor tips.

Reviewed by Dr. Jen Lincoln, November 2018


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