What Are The Early Signs Of Pregnancy?
Lisa Scott
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
fertilization). The medical term for a pregnant woman is
genetalian, just as the medical term for the potential baby is
embryo (early weeks) and then fetus (until birth).
A woman who is pregnant for the first time is known as a
primigravida or gravida 1: a woman who has never been pregnant
is known as a gravida 0; similarly, the terms para 0, para 1
and so on are used for the number of times a woman has given
birth.
In many societies medical and legal definitions, human
pregnancy is somewhat arbitrarily divided into three trimester
periods, as a means to simplify reference to the different
stages of fetal development.
The first trimester period carries the highest risk of
miscarriage (natural death of embryo or fetus). During the
second trimester the development of the fetus can start to be
monitored and diagnosed. The third trimester marks the
beginning of viability, which means the fetus might survive if
an early birth occurs.
Before pregnancy begins, a female oocyte (egg) must join, by
male spermatozoon in a process referred to in medicine as
"fertilization", or commonly (though perhaps inaccurately) as
"conception."
In most cases, this occurs through the act of sexual
intercourse, in which a man ejaculates inside a woman, thus
releasing his sperm. Though pregnancy begins at implantation,
it is often convenient to date from the first day of a woman's
last menstrual period. This is used to calculate the Estimated
Date of Delivery (EDD).
Traditionally (according to Naegele's rule, which is used to
calculate the estimated date of delivery, or EDD), a human
pregnancy is considered to last approximately 40 weeks (280
days) from the last menstrual period (LMP), or 37 weeks (259
days) from the date of fertilization. However, a pregnancy is
considered to have reached term between 37 and 43 weeks from
the beginning of the last menstruation. Babies born before the
37 week mark are considered premature, while babies born after
the 43 week mark are considered postmature.
According to Merck, the norm for human pregnancy is that it
lasts 266 days from the date of fertilization. This is 38
weeks, or approximately 8 Gregorian months and 22.5 days, or
9.0 lunar months). Counting from the beginning of the woman's
last menstrual cycle, the norm is 40 weeks (the basis for
Naegele's rule).
According to the same reference, less than 10% of births occur
on the due date, 50% of births are within a week of the due
date, and almost 90% within two weeks. But it is not clear
whether this refers to the due date calculated from an early
sonograph or from the last menstruation (see further down).
Though these are the averages, the actual length pregnancy
depends on various factors. For example, the first pregnancy
tends to last longer than subsequent pregnancies.
An accurate date of fertilization is important, because it is
used in calculating the results of various prenatal tests (for
example, in the triple test). A decision may be made to induce
labour if a baby is perceived to be overdue. Due dates are only
a rough estimate, and the process of accurately dating a
pregnancy is complicated by the fact that not all women have 28
day menstrual cycles, or ovulate on the 14th day following their
last menstrual period. Approximately 3.6% of all women deliver
on the due date predicted by LMP, and 4.7% give birth on the
day predicted by ultrasound.
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. 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 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.
About The Author: The early signs of pregnancy vary from woman
to woman; some may have all the signs in the book and others
may have just a few or none.
http://1earlysignsofpregnancy.info
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