Most women make various healthy lifestyle changes as soon as they decide to have a baby. The most intriguing thing about the initial two weeks is that they are considered part of your pregnancy even though you do not conceive before week 3.
What happens in your body in pregnancy weeks 1 and 2?
There are usually no detectable signs of pregnancy during the first week because you are not even pregnant yet. Doctors calculate an approximate due date from the first day of your last menstrual cycle  as it is impossible to decide exactly when ovulation occurs and the egg gets fertilized. So, only around 5% women give birth on their due date.
Your body lays the groundwork for pregnancy every month during period as various complex hormonal changes occur in the body  in case conception occurs within a fortnight. This is why doctors consider the beginning of your last period as the starting of your pregnancy. The ovaries release a certain number of eggs each month approximately 14 days before the first day of your next period , which then matures in a follicle (fluid filled sac) .
Just one matured egg is then ovulated (released from the follicle) to travel down the fallopian tube and await fertilization . The rest of the eggs are terminated and reabsorbed by the ovary within 24 hours .
Changes in the hormonal (human chorionic gonadotropin or hCG) levels also take place during this time as your body gets ready for pregnancy. 
Your Baby at 1 and 2 Weeks of Pregnancy
Your baby (or the embryo) still does not exist as the egg has not yet fertilized .
Are there any tests for detecting pregnancy at weeks 1 and 2?
It is still too early to find out whether you are pregnant or not by scanning tests like ultrasound.
Are there any detectable signs and symptoms of pregnancy weeks 1 and 2?
No two pregnancies are the same or have the same symptoms at the same time. You may not have any idea about the changes occurring in your body at this stage as you are yet to miss a period. Many women do not have any noticeable symptoms before the missed period while others may experience the following, especially during the second week:
- Nausea (morning sickness)
- Fatigue 
- Constipation 
- Breast tenderness
- Intense Dreams
- Back pain and/or neck pain
- Increased vaginal discharge 
- Light menstrual bleeding or spotting (rare cases; check with your doctor for any abnormalities)
Tips for a Healthy Pregnancy
- Visiting your ob-gyn before conception for determining the risks of any genetic disease 
- Finding out about any necessary lifestyle changes for a healthy pregnancy (e.g. giving up smoking, alcohol and drugs)
- Asking the ob-gyn about potential environmental hazards that may affect your pregnancy
- Consulting your doctor regarding the required daily amount of folic acid (taking 0.4 milligrams of folic acid daily before conception considerably reduces the risk of neural tube defects) 
- Following a regular exercise routine to stay active 
- http://www.bounty.com/pregnancy/1-week-pregnant [/ref]