This is one of the most crucial stages of pregnancy as this is the week when you conceive . Many women do not know they are pregnant until week 3 as there are often no visible signs of pregnancy. Pay a visit to your doctor to find out what you can expect from your pregnancy and learn more about early pregnancy symptoms.
Pregnant women learn about being 3 weeks pregnant usually because they have missed their menstrual period. It is a prompt to take a pregnancy test. Sometimes, the result of a pregnancy test can be a false positive. Thus, going to the doctor is still the most certain way.
Changes in Your Body during Pregnancy Week 3
Your body has just started producing estrogen and progesterone, the hormones responsible for most bodily changes during pregnancy . However, no detectable changes, such as increased belly size, occur at this point.
The HCG (Human Chorionic Gonadotropin) Levels
The placental cells start producing hCG (pregnancy hormone) immediately after implantation . The hCG level then continues to increase until around 8-12 weeks, when it stabilizes or drops. The higher the hCG levels, the more evident the symptoms .
Development of Your Baby During Week 3 Pregnancy
The matured egg that travels down the fallopian tube gets fertilized by a single sperm out of around 300 million . This successful sperm has to travel 6-8 inches up the uterus before it can reach the egg waiting for fertilization. It takes around 20 minutes to penetrate the hard outer layer of the egg and within the next eleven hours, the nuclei of the sperm and the egg merge with each other, completing the fertilization process, resulting in a fertilized egg .
The egg and the sperm contain 23 chromosomes each, which then combine to form the zygote containing 46 chromosomes . The gender of the baby is decided the moment the egg gets fertilized, depending on whether the sperm fertilizing it carries an X chromosome or a Y chromosome. Other prominent chromosomal traits such as hair color, eye color, and body type are also determined at this stage .
The newly formed zygote travels up the fallopian tube towards the uterus where it gets attached to the uterine wall for further development (implantation) . The implantation process completes 6 to 12 days (9 days on average) after ovulation and fertilization . In the meantime, the zygote continues dividing to form a cluster of around 100 cells (blastocyst) . In some rare cases (about 2% of pregnancies), the blastocyst attaches itself somewhere in the fallopian tube, ovary, abdomen or cervix, leading to an ectopic pregnancy or miscarriage .
Moreover, the amniotic sac is starting to form. This so-called amniotic sac filled with amniotic fluid that surrounds and protects the embryo. The outer layer of this sac will develop into the placenta. Once the placenta has been fully formed, it will be the source of nutrients for the embryo. The placenta is considered a one-stop for your baby’s essentials.
What to Expect at 3 Weeks Pregnant?
Your baby at 3 weeks pregnant is about the size of a pinhead. This means the embryo is still very tiny. This is the beginning of a new chapter in your life. As one of the many pregnant women who went through the same thing, there is nothing to worry about as long as you will be extra careful with your self from now on.
During this time, your 3 weeks pregnant belly is still pretty much your not-pregnant belly showing no sign of pregnancy. But prepare yourself because it’s about to grow!
Signs and Symptoms at Pregnancy Week 3
It is important to note that signs and symptoms are two different things. Signs are those experienced by the individual while symptoms are occurrences that others can identify but the affected individual cannot.
3 Weeks Pregnant Signs
Most women experience the implantation spotting or bleeding within 1-2 days after implantation . The fertilized egg attaching itself into the uterine lining is causing the implantation bleeding. This is normal so do not let a little blood freak you out.
Additional 3 weeks pregnant signs may include:
- Increased basal body temperature 
- Lower abdominal cramping
- Decreased consistency of cervical mucus or vaginal discharge 
- Nausea (morning sickness)
- Breast tenderness or soreness
- Gas and bloating
- Lowe back pain
- DIarrhea (rarely)
3 Weeks Pregnant Symptoms
These signs and symptoms are also similar to the ones women experience during premenstrual syndrome or PMS. Thus, knowing the difference between the signs and symptoms during pre-period and being pregnant.
Some 3 weeks pregnant symptoms are:
- Mood swings
- Food cravings 
- Food aversion
Tests and Exams for Pregnancy Week 3
Most pregnancy tests detect conception based on the hCG levels in the urine. So, conception can be detected by a home pregnancy test during the third week , 5-6 days following implantation. Blood pregnancy tests give positive results 3-4 days after implantation .
At week 3, the baby is just a tiny ball of cells which cannot be detected by scanning exams like ultrasound. The main purpose of an ultrasound is to identify if the fetus really exists or not. Basically, confirm the pregnancy through the presence of the gestational sac. At this stage of early pregnancy, the gestational sac allows the embryo to enclose the amniotic fluid inside the amniotic sac.
Tips for a Healthy Pregnancy
Most women do not find out they are pregnant before the third week. So, this is the time to make all the dietary and lifestyle changes necessary for a healthy pregnancy and baby. Pregnant women are expected to drop all vices, other unhealthy practices and more.
- Giving up alcohol and tobacco
- Cutting down your caffeine intake
- Making sure to inform the health care practitioner about your pregnancy before taking an x-ray for any health issues (e.g. dental ailments) as an x-ray is often not recommended during early pregnancy 
- Avoiding going near hazardous substances such as pesticides (it may hamper the cell division)
- Taking prenatal vitamins containing folic acid (0.4 milligrams daily) as it prevents most birth defects involving the brain and spinal cord most likely to occur during the first few weeks  Moreover, prenatal vitamins with folic acid also help in preventing the risk of having a fetus that’s smaller for his gestational age. It is also best to take vitamins that have vitamins A, E, C, calcium, and zinc.
- http://www.webmd.com/baby/folic-acid-and-pregnancy [/ref]