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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.


Moodiness You 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 cramps You 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!

Blastocyst  --------------->




Uterine cavity











Uterine lining



(Week 2)

Of Note This Week

Am I Pregnant?

Take this online pregnancy test to find out the chance that you are pregnant.

Videos of Interest:

Month One:  via Discovery Health

The First Two Weeks:  via Nova Online

Embryo Development & Implantation: via RUDmedical