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, cravings for certain foods that are not normally
sought out, 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).
Breast tenderness is common during the first trimester, and is more
common in women who are pregnant at a young age.
Pregnancy detection can be accomplished using one or more various
pregnancy tests, which detect hormones generated by the newly formed
placenta. Clinical blood and urine tests can detect pregnancy 12 days
after implantation. Blood pregnancy tests are more accurate than urine
tests. Home pregnancy tests are urine tests, and normally cannot detect
a pregnancy until at least 12 to 15 days after fertilization. A
quantitative blood test can determine approximately the date the embryo
was conceived.
In the post-implantation phase, the blastocyst secretes a hormone named
human chorionic gonadotropin, which in turn stimulates the corpus luteum
in the woman's ovary 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.
Despite all the signs, some women may not realize they are pregnant
until they are quite far along in their pregnancy. In some cases, a few
women have not been aware of their pregnancy 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 obstetric ultrasonography 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. Without symptoms such as morning
sickness, 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. 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. The due date can be calculated by using Naegele's
rule. The expected date of delivery may also be calculated from sonogram
measurement of the fetus. This method is slightly more accurate than
methods based on LMP. Additional obstetric diagnostic techniques can
estimate the health and presence or absence of congenital diseases at an
early stage.
Pregnancy test
A pregnancy test attempts to determine whether or not a woman is
pregnant. Modern pregnancy tests look for chemical markers associated
with pregnancy. These markers are found in urine and blood, and
pregnancy tests require sampling one of these substances. The first of
these markers to be discovered, human chorionic gonadotropin (hCG), was
discovered in 1930 to be produced by the trophoblast cells of the
fertilised ovum (blastocyst). While hCG is a reliable marker of
pregnancy, it cannot be detected until after implantation: this results
in false negatives if the test is performed during the very early stages
of pregnancy. Obstetric ultrasonography may also be used to detect
pregnancy. Obstetric ultrasonography was first practiced in the 1960s;
the first home test kit for hCG was released in the mid-1970s.
The test for pregnancy which can give the quickest result after
fertilisation is a rosette inhibition assay for early pregnancy factor (EPF).
EPF can be detected in blood within 48 hours of fertilization. However,
testing for EPF is expensive and time-consuming.
Most chemical tests for pregnancy look for the presence of the beta
subunit of hCG or human chorionic gonadotropin in the blood or urine.
hCG can be detected in urine or blood after implantation, which occurs
six to twelve days after fertilization. Quantitative blood (serum beta)
tests can detect hCG levels as low as 1 mIU/mL, while urine tests have
published detection thresholds of 20 mIU/mL to 100 mIU/mL, depending on
the brand. Qualitative blood tests generally have a threshold of 25 mIU/mL,
and so are less sensitive than some available home pregnancy tests. Most
home pregnancy tests are based on lateral-flow technology.
With obstetric ultrasonography the gestational sac sometimes can be
visualized as early as four and a half weeks of gestation (approximately
two and a half weeks after ovulation) and the yolk sac at about five
weeks' gestation. The embryo can be observed and measured by about five
and a half weeks. The heartbeat may be seen as early as six weeks, and
is usually visible by seven weeks' gestation.
Pregnancy tests may be used to determine the viability of a pregnancy.
Serial quantitative blood tests may be done, usually 2–3 days apart.
Below an hCG level of 1,200 mIU/ml the hCG usually doubles every 48–72
hours, though a rise of 50–60% is still considered normal. Between 1,200
and 6,000 mIU/ml serum the hCG usually takes 72–96 hours to double, and
above 6,000 mIU/ml, the hCG often takes more than four days to double.
Failure to increase normally may indicate an increased risk of
miscarriage or a possible ectopic pregnancy.
Ultrasound is also a common tool for determining viability. A lower than
expected heart rate or missed development milestones may indicate a
problem with the pregnancy.[9] Diagnosis should not be made from a
single ultrasound, however. Inaccurate estimations of fetal age and
inaccuracies inherent in ultrasonic examination may cause a scan to be
interpreted negatively. If results from the first ultrasound scan
indicate a problem, repeating the scan 7–10 days later is reasonable
practice.
