To
help you follow some of the changes
you may encounter during your pregnancy
this section is divided into "month
by month" segments. Each month
tells what you can expect as your pregnancy
progresses. It focuses on:
Also,
you can find links back to information
and tests that might take place during
a particular month. Just click on the
months to the left to go to the pages
that contain more information on that
particular month.
Estimating
Gestational Age
What
is gestational age?
Why is it important
to know the gestational age?
How is gestational
age calculated?
One
of the most frequent questions you
will probably hear from friends and
acquaintances when you tell them you
are pregnant is "How far along are
you?" or "When you are due?" Your
health care provider will estimate
the gestational age of your baby at
one of your first prenatal appointments.
While this is just an estimate (only
about 5% of babies are born on their
estimated due date), it is important
to know the approximate gestational
age when monitoring your pregnancy.
What
is gestational age?
Gestational
age is the age of an unborn baby. It
is measured in weeks and days, not
in months. Since the precise
date of conception is seldom known,
the age is based on the date of the
mother's last menstrual period. Forty
weeks after the first day of the
last menstrual period is the estimated
end of a normal term pregnancy, or
due date.
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Why
is it important to know the gestational
age?
The
progress of a pregnancy can be judged
as normal or abnormal only when the
gestational age is accurately known. Gestational
age is very important when complications
occur in the pregnancy and early
delivery may be necessary. It
is also important to know gestational
age so that an overdue baby can be
carefully monitored.
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How
is gestational age calculated?
The
gestational age of a baby may be
calculated from the date of your
last period. If you are sure
of this date and have regular periods,
your due date is estimated to be
40 weeks from the first day of your
last period. An early exam
of the uterus and
an early positive pregnancy test
also help determine gestational age.
The
most accurate way to determine gestational
age is a reliable date for the last
menstrual period confirmed by an
ultrasound exam. The baby can
be measured with ultrasound as
early as 5 or 6 weeks after the mother's
last menstrual period. This
method is most accurate in early
pregnancy. It becomes less
accurate late in pregnancy. The
best time to date a pregnancy with
ultrasound is between the 8th and
18th weeks of pregnancy.
Women
who have undergone special procedures
to become pregnant, such as artificial
insemination or in vitro fertilization,
usually know exactly when conception
occurred. In these cases there
is no doubt about the baby's gestational
age.
It can be difficult to determine accurately a baby's
gestational age and your due date if:
- You
have irregular periods.
- You
cannot remember the date of your
last period.
- The
baby is unusually large or small.
- The
due date based on the last menstrual
period does not correspond with
the size of the uterus early in
pregnancy or with the height of
the fundus (top
of your uterus) as pregnancy progresses.
Some
health care providers use early ultrasound
to estimate gestational age and due
dates for all pregnant women. Your
provider may not feel that early
ultrasound is necessary in your case.
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