The World Health Organization defines normal term for delivery as between 37 weeks and 42 weeks The calculation of this date involves the assumption of a regular 28-day menstrual cycle.
One scientific term for the state of pregnancy is gravid, and a pregnant female is sometimes referred to as a gravida. The term embryo is used to describe the developing offspring during the first 8 weeks following conception, and the term fetus is used from about 2 months of development until birth.
The expected date of delivery (EDD) is 40 weeks counting from the last menstrual period (LMP), and birth usually occurs between 37 and 42 weeks.
The beginning of pregnancy may be detected in a number of different ways, either by a pregnant woman without medical testing, or by using medical tests with or without the assistance of a medical professional.
Most pregnant women experience a number of symptoms, which can signify pregnancy. The symptoms can include nausea and vomiting, excessive tiredness and fatigue, craving for certain foods not normally considered a favorite, and frequent urination particularly during the night.
A number of early medical signs are associated with pregnancy. These signs typically appear, if at all, within the first few weeks after conception. 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 the presence of human chorionic gonadotropin (hCG) in the blood and urine, missed menstrual period, implantation bleeding that occurs at implantation of the embryo in the uterus during the third or fourth week after last menstrual period, increased basal body temperature sustained for over 2 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 uterus isthmus), and pigmentation of linea alba - Linea nigra, (darkening of the skin in a midline of the abdomen, caused by hyperpigmentation resulting from hormonal changes, usually appearing around the middle of pregnancy).
Pregnancy detection can be accomplished using one or more of various pregnancy tests, which detect hormones generated by the newly formed placenta. Clinical blood and urine tests can detect pregnancy 12 days after implantation , which is as early as 6 to 8 days after fertilization. Blood pregnancy tests are more accurate than urine tests. Home pregnancy tests are personal urine tests, which normally cannot detect a pregnancy until at least 12 to 15 days after fertilization. Both clinical and home tests can only detect the state of pregnancy, and cannot detect the age of the embryo.
Despite all the signs, some women may not realize they are pregnant until they are quite far along in their pregnancy, in some cases not even until they begin labour. This can be caused by many factors, including irregular periods (quite common in teenagers), certain medications (not related to conceiving children), and obese women who disregard their weight gain. Others may be in denial of their situation.
An early sonograph can determine the age of the pregnancy fairly accurately. In practice, doctors typically express the age of a pregnancy (i.e., an "age" for an embryo) in terms of "menstrual date" based on the first day of a woman's last menstrual period, as the woman reports it. Unless a woman's recent sexual activity has been limited, she has been charting her cycles, or the conception is the result of some types of fertility treatment (such as IUI or IVF), the exact date of fertilization is unknown.
Often the only visible sign of a pregnancy is an interruption of the woman's 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 2 weeks later than the first day of the woman's last menstrual period.
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