 SYMPTONS OF PREGNANCY
Pregnancy is the carrying
of one or more embryos or fetuses by female mammals, including humans,
inside their bodies.
In a pregnancy, there can
be multiple gestations (for example, in the case of twins, or
triplets). Human pregnancy is the most studied of all mammalian
pregnancies.
Human pregnancy lasts approximately 9 months between the time
of the last menstrual cycle and childbirth (38 weeks from
fertilisation). The medical term for a pregnant woman is genetalian,
just as the medical term for the baby is embryo (early weeks) and then
fetus (until birth).
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. |
Pregnancy Symptoms
The beginning of pregnancy may
be detected in a number of ways, including various pregnancy tests
which detect hormones generated by the newly-formed placenta. Clinical
blood and urine tests can detect pregnancy soon after implantation,
which is as early as 6-8 days after fertilization.
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. Pregnancy tests
detect the presence of human chorionic gonadotropin.
An early ultrasound 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, the exact date of fertilization is unknown.
Absent 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
margin of error is 0 to 30 days after last menstruation, hence a 14
day average.) 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.
An ultrasound of a developing fetus. There are likewise finer
distinctions between the concepts of fertilization and the actual
state of pregnancy, which starts with implantation. In a normal
pregnancy, the fertilization of the egg usually will have occurred in
the Fallopian tubes or in the uterus. (Often, an egg may become
fertilized yet fail to become implanted in the uterus.) If the
pregnancy is the result of in-vitro fertilization, the fertilization
will have occurred in a Petri dish, after which pregnancy begins when
one or more zygotes implant after being transferred by a physician
into the woman's uterus. |
