What is the normal size of the gestational sac at six weeks?
Gestation
refers to the period when the fetus grows and develops in the uterus. It is the
time between the conception and birth of the embryo.
Beginning with
fertilization, it ends with the birth of the baby. A gestational period
describes the length of the pregnancy period and can range between 38 to 42
weeks.
What is a gestational sac?
A gestational sac is a spherical shaped fluid-filled cavity that is present
around the embryo. It is situated in the upper part of the uterus’s fundus.
Appearing as an echogenic ring, it surrounds a sonolucent center.
The
availability of this structure within the womb is the only indication of
pregnancy, before the identification of the embryo. The gestational sac
encloses the baby that is developing. It contains extraembryonic coelom or the
chorionic cavity in the early stages of embryogenesis.
The amniotic fluid is
also found in it. It is located around a white rim and is a dark space itself.
Structure and Development
The gestational sac is the earliest finding in sonography during pregnancy.
Generally located within the uterus, the gestational sac is spherical. It takes
around four weeks for the gestational sac to appear.
It then follows a growth
rate of about 1 mm per day for about nine weeks. The size of a gestational sac
is determined by the measurement of the largest diameter or by calculating a
mean of the diameters.
In the embryogenesis stage, the gestational sac is a part of the extraembryonic
coelom. Being a portion of the conceptus, it consists of a cavity between the
Trophoblast and Heuser’s membrane. The amniotic sac occupies most of the
gestational sac by nine weeks of gestational age.
The gestational sac can be recognized within four weeks of the last menstrual
period. With a size of about 2 mm at first, it gradually increases to 5-6 mm by
five weeks. Thereby, the average increasing speed becomes one millimeter per
day.
While the yolk sac becomes visible by around the 5th week of the gestation
period and attains the size of 6 mm by ten weeks. These yolk sacs disappear by
the 12th week on an average.
By
the time the fifth week-ends, the fetal pole becomes visible. This is the time
when the embryo is first seen. It looks like a tissue nubbin, adjacent as well
as distinct from the yolk sac.
At this time, the length of the embryo is about
2 mm, and it develops along the yolk sac’s chorionic margin. By the sixth week,
it looks like a 5 mm echogenic disk which is attached to the yolk sac and is
touching and closing tangentially.
In
case there is no gestational sac seen in the ultrasound, it can either mean an
ectopic pregnancy or a miscarriage. In case the gestational sac is found empty,
it can be an anembryonic pregnancy and suggests that the embryo has failed to
develop.
With
the presence of innovative medical technologies in India, there are some best gynecologist in Chennai, Mumbai,
Kolkata and other Indian states. This has made the entire pregnancy process
smoother.
This article gives the reader a brief idea of what a gestational sac
and about its structure. It helps in understanding how an embryo develops
during the gestational period.
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