While your doctor measures your pregnancy in weeks starting with the first day of your last period, you might more logically consider conception as the start of pregnancy. Many women have few, if any, symptoms two weeks after conception -- around the time of the first missed menses. Others have classic symptoms almost from the first day of a missed period, often caused by the hormonal changes of pregnancy.
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As early as one to two weeks after conception, a woman may notice changes in her breasts. An increase in estrogen causes breasts to feel fuller, more tender and more sensitive than usual. Nipples might become hypersensitive, feeling tense and tingly. You might notice more blue lines -- veins -- on your breasts, as well as a darkening of your nipples.
One of the best-known and common symptoms of early pregnancy, affecting up to 90 percent of all pregnant women, nausea can start as early as the first missed period. Rising levels of human chorionic gonadotropin, the hormone detected in pregnancy tests and a heightened sense of smell are the main culprits. Some women experience nausea only at certain times of the day, such as the common morning sickness, while others may feel slightly ill all day. Nausea may or may not be accompanied by vomiting.
Many women feel more tired during the early weeks of pregnancy. Increasing levels of the hormone progesterone, lower blood sugar levels, and lower blood pressure combine early in pregnancy to drain energy. Going for a brisk walk or chewing mint-flavored gum may help boost energy, at least temporarily.
You might notice this symptom if you took your temperature daily to determine when to have sex to get pregnant. Your basal body temperature -- taken first thing in the morning -- remains elevated for more than two weeks, or past the time when you would have expected your menstrual period. Progesterone, produced by the growing embryo and placenta, keeps your temperature approximately 0.5 to 1 higher than your normal baseline if you're pregnant.