skin, nails, and hair, the lens of the eye, the lining of the internal and external ear, the nose and sinuses, the mouth, the anus, tooth enamel, the pituitary and mammary glands, and all the parts of the nervous system.  This truly is the beginning of a complete human being!

 

Neural Tube  The primitive streak appears as a groove on the surface of the embryo, stretching from the bottom to the middle of the embryo.  Shortly after it appears, another group of cells will gather to form another groove on top of the primitive streak.  The two grooves will join and then stretch to cover the entire length of the embryo.  The groove will then deepen, and the sides of the groove will flatten, curve up, and then join together to form a circular tube, first joining in the center of the embryo, and then in a zipper-like fashion, joining down to the bottom and then up to the top.  This neural tube will house the spine and is the beginning of the central nervous system.  This important development will eventually integrate the actions of all the systems in your baby's body!

 

Somites  With the zipper-like motion of the neural tube closing together, three pairs of small bumps form on either side of the closure.  These are the somites, and they will form the skeleton and the major muscles of the body.  Thirty-eight pairs of somites will line the neural tube within 2 weeks. 

 

Heart  Within the yolk sac, groups of cells clump together to form "blood islands."  These blood islands elongate to form blood vessels, which connect to one another, and blood cells begin to form within these blood vessels.  More blood islands begin to form within the mesoderm of the embryo, and as they develop into blood vessels, some of them join together to form a larger tube directly beneath the spinal cord.

 

Week 3

 

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What is happening in my body?  It has been 3 weeks since conception, and you are considered 5 weeks LMP by your obstetrician. Last week we learned how the embryo buried into the uterine lining and tapped into the maternal blood system through the newly formed umbilical cord.  Even though numerous events have been going on inside of you, you probably don't know that you're pregnant yet.  This week, however, that is likely to change.  As the embryo continues to develop, more and more HCG is secreted, and because of this, you will skip a period.  You may also experience some or all of the following symptoms.  These will vary in intensity from woman to woman and even from pregnancy to pregnancy in the same woman.  You may have no symptoms and still have a perfectly healthy pregnancy.

 

Fatigue  It's normal for you to be exhausted as your body begins to make new hormones and assist in the development of your baby.  You'll need time to adjust to the shift in metabolism - the calories you take in are going to be routed to your baby for use, and that can leave you feeling less energetic.  Try to eat healthy foods: lots of fruits and vegetables, whole grains, etc., and try to do a small amount of exercise to help combat this lack of energy.  Just getting outside and breathing some fresh air will do wonders for your energy level. 

 

Breast Changes  Your breasts may feel sore and tender.  This is because blood flow to the breasts is increasing to prepare for the growth and development of the breast glands and ducts in the next few weeks.  Breast cells will start to increase in number as well, and you may notice that your breasts have begun to swell because of this.  A supportive bra will help deal with most of the soreness. 

 

Morning Sickness  Hopefully you'll make it through your pregnancy without a shred of morning sickness, but 70-80% of women do experience some sort of nausea.  No one knows the real cause of morning sickness, but it is commonly thought that the high levels of HCG and/or progesterone could be the culprit.  On the positive side, studies have shown that women with morning sickness have fewer miscarriages. 

 

Frequent Urination  Your growing uterus will start to push on your bladder this week, and you may need to run to the bathroom frequently.  There's not much you can do about this, but cutting down on drinking fluids before bedtime might help to end those middle-of-the-night trips.

 

Hunger  When you're not busy being nauseated, you might find that you are ravenous.  You may also crave particular foods.  This doesn't give you license to eat as much cheesecake as you like, but it's okay to indulge a little now and then.  While you are technically eating for two, your body only needs 300 more calories a day to do it's work, and in reality this means that if you added an extra apple a day, you'd be eating enough.

 

What if I spot or get my period?  It's actually very common for women to spot or have light period-like bleeding when they are newly pregnant.  This is not an actual period, although it can be easily confused with one, especially if you do not know beforehand that you are pregnant.  Bleeding at this time during your pregnancy can be caused by several things.

 

-  Implantation spotting is caused by the embryo burrowing into the lining of the uterus. This action shreds some of the uterine lining, and it gradually descends into the vagina.  Implantation spotting is usually very light pink or brown, and it usually only lasts a day or two. 

 

-  If you became pregnant while taking the birth control pill, chances are you kept taking it and didn't know you were pregnant right away.  Taking the last week of pills, the "placebo" pills, will cause the progesterone in your bloodstream to drop, and this may cause some light spotting.  However, the hormones should not drop low enough for you to have a miscarriage.  Bleeding of this nature would appear as a normal menstrual flow, except it will probably be lighter and may not last as long.

 

-  Early pregnancy bleeding can signal a problem, but more than half of the time, it does not.  This kind of bleeding most commonly results when the hormone levels aren't high enough for all of the lining to remain on the uterus or when there are chromosomal abnormalities in the embryo. If the hormone levels are too low, you may need to be put on a synthetic progesterone so that you will have enough in your bloodstream to keep from miscarrying.  Other times, the body quickly adds more progesterone and things are fine. This bleeding will appear as a normal menstrual period would, except it will probably be lighter and may not last as long.  If there is a chromosomal abnormality in the embryo, early pregnancy bleeding can signal a miscarriage.  This bleeding may appear as a normal/heavy menstrual period and will probably involve cramping.

 

What is happening with my baby?  This week is a busy week for your little one!  By the end of the week, your baby will measure 1/8 inch long and the amniotic sac will be about the size of a grape, making a teeny bump, 1/3 inch long,

 

off the side of the uterus.  By midweek, a fold of tissue that will be the baby's head can be seen, and the rest of the body begins to unfold and lengthen, giving rise to the chest and abdominal cavities.  The thyroid gland also begins to form this week.  Here are the details on the major things that are happening with your baby this week.

 

Gastrulation  Last week we saw how the embryo formed a primitive streak, which gives the embryo direction as it grows.  Once the streak is present, cells begin to move around to form three distinct layers:  the endoderm, mesoderm, and ectoderm.  These layers will give rise to every cell type and organ.  The inner layer of cells, the endoderm, will form your baby's glands, the lining of the lungs, the tongue and tonsils, the urethra and bladder, and the digestive tract. The middle layer of cells, the mesoderm, will form the muscles and bones, the lymphatic tissue, the spleen, the heart and blood cells, the lungs, and the reproductive and excretory systems.  The outer layer of cells, the ectoderm, will form the 

 

Week 3 Belly Shot

 

Embryo Implanted on the Uterine Lining

 

The primitive streak can be seen on the left side of this embryo.

 

The primitive streak can still be seen, and the opposite end of the embryo is starting to fold up.

 

The neural tube is seen along with somites on either side of it. 

 

Videos

 

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 gastrulation, cell migration and differentiation, and genes. Running time 07:47. From Nova Online.

 

Quicktime movie of an embryo developing from 3 to 8 weeks.

 

Neural tube formation from day 15 to day 28. Slow to download but very helpful. 

 

Of Note This Week

 

Check this list to find out which tests are the most sensitive.

 

(5 weeks since your last period)