According to WebMD, the symptoms of pregnancy at four weeks are a missed period and possible light spotting as implantation of the embryo occurs in the uterus. When a woman is four weeks pregnant, the egg containing the fetus has only recently been fertilized. This means that some women may not notice any symptoms of pregnancy at four weeks.
As described by the Mayo Clinic, the due date for a baby is calculated by adding 40 weeks to the first day of a woman's last actual period. Ovulation, which is the time when a baby can actually be conceived, usually occurs about two weeks before a woman's next missed period, according to WebMD. This means that a woman who is four weeks pregnant has likely only carried a fetus for about two weeks.
According to Dr. Daniel Lee and Dr. Kristine Eule, pregnant women produce the hormone HCG. This hormone can cause some symptoms such as anxiety, nausea, vomiting, fainting, dizziness, exhaustion and mood swings. Some women may experience soreness or tenderness in their breasts. Some women also experience a heightened sense of smell that may induce nausea or vomiting. These symptoms tend to subside once the first trimester is over.