What are the signs of pregnancy at four weeks?

Two signs during the 4th week of pregnancy are implantation cramping or spotting and a missed period, according to WebMD. Morning sickness begins as early as three weeks into the pregnancy, according to the Mayo Clinic, which is weeks three to five of pregnancy, depending on when conception occurred.

Other early pregnancy symptoms include fatigue, frequent urination, mood swings, an aversion to smells or foods, food cravings and swollen or painful breasts. This is also the week to take a pregnancy test, as the chance of getting a positive result before a missed period is very slim, according to About.com.