Pregnancy

A number of medical signs are associated with pregnancy. Although not all of these signs are universally present, nor are all of them diagnostic by themselves, taken together they make a presumptive diagnosis of pregnancy. These signs include increased basal body temperature sustained for over two weeks after ovulation, Chadwick's sign (darkening of the cervix, vagina, and vulva), Goodell's sign (softening of the vaginal portion of the cervix), Hegar's sign (softening of the Vaginal fornix), and Linea nigra, (darkening of the skin in a vertical line on the abdomen, caused by hyperpigmentation resulting from hormonal changes; it usually appears around the middle of pregnancy).

The beginning of pregnancy may be detected in a number of ways, including various pregnancy tests which detect hormones generated by the newly-formed trophoblast (early placenta). Modern clinical blood and urine tests can detect pregnancy soon after implantation, which is as early as 6-8 days after fertilization. Home pregnancy tests are personal urine tests, which normally cannot detect a pregnancy until at least 12-15 days after fertilization. Both clinical and home tests can only detect the state of pregnancy, and cannot detect its age.

In the post-implantation phase, the blastocyst secretes a hormone named human chorionic gonadotropin (HCG) which in turn, stimulates the corpus luteum (the are in the ovary that released the egg) to continue producing progesterone. This acts to maintain the lining of the uterus so that the embryo will continue to be nourished. The glands in the lining of the uterus will swell in response to the blastocyst, and capillaries will be stimulated to grow in that region. This allows the blastocyst to receive vital nutrients from the woman.

In practice, doctors typically express the age of a pregnancy in terms of "menstrual date" based on the first day of a woman's last menstrual period, as the woman reports it. In the absence symptoms such as morning sickness, often the only visible sign of a pregnancy is an interruption of her normal monthly menstruation cycle, (i.e. a "late period"). Hence, the "menstrual date" is simply a common educated estimate for the age of a fetus, which is an average of two weeks later than the first day of the woman's last menstrual period. The term "conception date" may sometimes be used when that date is more certain, though even medical professionals can be imprecise with their use of the two distinct terms. Confinement begins on the day predicted by LMP 3.6% of the time and on the day predicted by sonography 4.3% of the time. An early sonograph measurement of the fetus can determine the age of the pregnancy fairly accurately.