From the moment of conception, the baby's entire genetic makeup is determined. The
fertilized egg burrows itself into the side of mom's uterus, preparing for the lengthy
journey ahead. After just six days, one cell develops into nearly 200 and by the
end of the third week the brain begins to form. From Discovery Health.
Covers DNA combination, cell division, embryo implantation, and morning sickness.
Running time 04:58. From Nova Online.
What is happening in my body? It has been 2 weeks since conception, and you are considered
4 weeks LMP by your obstetrician. Last week, we learned that after the egg is expelled
from a follicle on the surface of an ovary, a corpus luteal cyst forms where the
follicle used to be. This corpus luteum secretes progesterone, and this secretion
will continue throughout your entire pregnancy. Progesterone is very important to
the development of your baby, and without it a pregnancy cannot be sustained within
the womb. Progesterone allows the lining of your uterus to get plush and thick.
When the developing blastocyst enters the womb it will now find a soft pillowy lining
to settle down on. Progesterone also tells your brain not to shed the uterine lining,
which would ultimately flush away the developing embryo before it could begin to
secrete its own protective hormone.
Breast tenderness Progesterone can make your breasts tender and sore. You might
also get sore nipples at this time. Many often think that breast changes are a sign
of pregnancy, but they are normal during any cycle. However, an increase in tenderness
can indicate pregnancy, as can tenderness when you normally don't have any.
Cervical fluid Your cervical fluid may alternate between dry and creamy. Some
women experience almost no cervical fluid, while other women have an abundance of
a white-to-yellow creamy cervical fluid. Any amount or type is normal at this time.
MoodinessYou may notice that you are more emotional during this time and these emotions
may change at the drop of a hat. Progesterone is the main culprit behind PMS, and
pregnancy is described by some as never-ending PMS. Not to worry though, you'll
look back fondly at the time you started crying during the cheesiest of commercials.
Menstrual crampsYou may experience some menstrual cramping as your progesterone
level stabilizes and your uterus adjusts to the new guest. This is perfectly normal,
however, anything that causes you severe pain should be reported to your doctor.
Implantation spotting We'll read about how the blastocyst will implant within the
uterine lining in a moment, but if you experience brown or pink spotting this week,
it could be due to the blastocyst implanting in your uterine lining. This does not
always occur with implantation, however, and most of the time you will not experience
any implantation spotting.
When will I get a positive pregnancy test? With a very sensitive pregnancy test,
the earliest possible time you can get a positive test is 7 days after ovulation.
The blastocyst implants in the uterine lining on average between 7 and 10 days after
ovulation occurs. As soon as the blastocyst implants, it begins to produce HCG (see
below). However, you're better off waiting until at least 10 days after ovulation
just to give it enough time. If your baby is a late-implanter, you may not show
a positive pregnancy test until after your period is due. Confused? The easiest
plan of action is to buy 2 tests. Take one 10 days after ovulation. If it is negative,
wait to see if your period comes. If it does not, wait until 16 days after ovulation
and take the second test. By then, it should be positive if you are pregnant.
What is happening with my baby?
Hatching The zona pellucida that protected the egg before it was fertilized still
surrounds the developing blastocyst, but during the beginning of this week, major
changes start to take place. The blastocyst secretes a chemical that dissolves some
of the zona pellucida. This allows for the blastocyst to "hatch" from the zona,
much like a chick hatches from an egg. The blastocyst leaves behind the protective
shell of the zona pellucida and is now floating freely within the uterus.
In this way, the embryo begins to nourish itself so that it can continue to grow.
Once the initial connection is made, the placenta begins to form between the chorion
and uterine lining. The placenta is a meeting place for the blood vessels from the
mother and the baby. The two systems are completely separate - the baby's blood
never mixes with the mothers, but they are deeply interconnected, meaning that the
baby cannot yet survive without the help of its mother. In the placenta, waste products
from the baby are discarded and fresh nutrients are picked up. Once the placenta
has begun to develop, the amnion forms around the embryo. Looking much like a bubble,
the amnion surrounds the embryo and collects fluid from surrounding maternal tissues.
The developing baby must be constantly bathed in fluids so that it will not get dried
out or become crushed within the uterus. The "bubble" becomes the amniotic sac that
will protect the baby until it is born, and its formation will be complete by the
end of this week.
Human Chorionic Gonadotropin (HCG) Once the embryo is connected to the mother, the
placenta secretes a hormone that is picked up by the maternal blood vessels. This
hormone is called human chorionic gonadotropin (HCG). HCG signals the corpus luteal
cyst on your ovary to stay put and continue to secrete more and more progesterone.
It is HCG that is credited to causing morning sickness, since it is the only hormone
secreted from outside of the maternal system.
Yolk Sac Shortly after the placenta and chorion have developed, a new formation
fully develops next to the embryo, called the yolk sac. The yolk sac contains no
yolk and no nutrients, but it produces blood cells for the embryo until the liver,
spleen, and bone marrow within the fetus have developed sufficiently enough for it
to produce its own blood cells. The yolk sac will also produce sex cells in the
future. Isn't it amazing that although your embryo is only a couple of weeks old
it is already preparing to reproduce?
Umbilical Cord Now that the embryo is connected to the maternal blood system, it
has a feast! For the next few days, the embryo will double in size - meaning that
if the baby continued to grow at this rate, it would be larger than the sun at birth!
(Thank goodness the rate of growth will slow in a few weeks!) Because of the rate
of growth and the constantly increasing need for food, an umbilical cord forms that
connects the embryo directly to the placenta. Blood is carried from the embryo along
the umbilical cord and into the placenta where it is brought close to the mother's
blood. Oxygen, nutrients, and antibodies from the mother make their way into the
embryo through a vein in the umbilical cord, and waste materials from the embryo
pass into the mother's blood through two arteries in the umbilical cord. This old
blood becomes enriched with more nutrients and oxygen, is cleaned of wastes, and
is then carried back to the embryo through the vein in the umbilical cord. At the
end of your pregnancy, the umbilical cord will move up to 300 quarts of blood each
day between you and your baby!
Implantation The blastocyst, now containing several hundred cells, soon lands on
the plush, pillowy lining of the womb. Commonly this occurs on the back wall of
the uterus. Cells on the outside of the blastocyst, known as the trophoblast, latch
onto the uterine lining and begin to secrete chemicals that are designed to erode
some of the lining away. As the chemicals go to work, the blastocyst tucks itself
away deep inside the lining of the uterus.
Some women experience spotting at this time, since some of the eroded lining may
make its way down through the cervix and into the vagina. When the blastocyst has
completely buried itself into the uterine lining, it is called an embryo.
Connection Once the cells of the trophoblast have dug deep enough into the lining,
the chemicals begin to rupture blood vessels within the uterus. When this happens,
the trophoblast develops into a tough membrane called the chorion. The chorion will
provide support and nourishment to your baby throughout the remainder of the pregnancy,
and it is the inner layer of the placenta. The chorion grows small fingerlike extensions
that branch out and tap into the ruptured blood vessels within the uterus.
Primitive Streak As this week draws to a close, a band of cells called the primitive
streak appears on the surface of the embryo. This streak forms a blueprint for the
embryo, giving it a front, a back, a top, bottom, and sides. The primitive streak
will guide the organization of all tissues, organs, and body systems for your baby!