Full term pregnancy is measured as 40 weeks, but the first day of pregnancy is counted as the first day of the last menstrual period. This means that at four weeks of pregnancy, a woman is just due for her menstrual period. Signs of pregnancy at four weeks aren't numerous, but there are a few, if you're very attuned to your body changes.
The most obvious sign of pregnancy at four weeks is that your period doesn't start. While some women experience spotting or a light, short period during the first month or two of pregnancy, the first indication of possible pregnancy is that their period doesn't show up on schedule. Implantation spotting, which occurs as the embryo burrows into the uterine wall, occurs 10 to 14 days after fertilization, according to the Mayo Clinic.
Many women have sore breasts right before their period every month, but the sore breasts of early pregnancy are more intense. It may actually hurt to touch your breasts and the tenderness may extend into your armpit. You may notice little bumps, called Montgomery's tubercles, becoming more prominent around your nipples, especially if this is your first pregnancy. Your breasts may also have more prominent veins than normal.
Rising progesterone levels from the burrowing embryo can create extreme fatigue, even in early pregnancy, according to the Mayo Clinic.
Although morning sickness becomes more prominent at six to eight weeks of pregnancy, some women notice a distaste for certain foods or an aversion to cigarettes or certain smells even as early as four weeks.
Women who are checking temperature readings to try and get pregnant may notice that their temperature remains elevated at the time of the missed period. If your temperature is elevated when you take it orally first thing in the morning more than two weeks after ovulation, and you're sure you know when ovulation occurred, it's a good sign that you're pregnant.
Around the time of a missed period, your cervix and the inside of the vagina will have a bluish tinge, called Chadwick's sign. While this isn't visible to women unless they're contortionists, your doctor will be able to see this during an internal exam.
Positive Pregnancy Tests
Some urine home pregnancy tests are accurate as early as the first day of a missed period. However, a negative reading doesn't mean you're not pregnant; some tests aren't sensitive enough to pick up positive results at four weeks. Check again in a few days. If you have a blood test done, the results are more accurate. Blood tests will detect a rise in hCG (human chorionic gonadotropin) levels by the day of a missed period in almost every case, according to the Advanced Fertility Center of Chicago.