First Trimester – Fetal Development




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The first two weeks of a pregnancy encompass the gestational period after conception occurs, which creates a two-week variance between what is referred to as the gestational age and the fetal age. The weekly tracking of the fetal age begins at week 3 of the gestational age. During the gestational period of the pregnancy, the menstrual cycle for the woman has ended, and her body is preparing for ovulation. Typically, ovulation will begin approximately 11-21 days after the first day of the last menstrual cycle. 

During intercourse, several hundred million sperm are released into the vagina, which travel through the woman’s cervix and into her fallopian tube.  If conception occurs, a sperm will penetrate the egg that is in the fallopian tube, creating a single set of 46 chromosomes that are referred to as a zygote.  The zygote represents the basis for a new human being!  The fertilized egg then begins traveling toward the uterus through the fallopian tube, which takes a couple of days.  The fertilized egg, which is dividing into cells and is now referred to as a morula, will eventually end up in the uterus, at which point it is referred to as a blastocyst.  Approximately 6-12 days after conception, the blastocyst will imbed itself into the lining of the uterus, where it will begin the embryonic stage of the pregnancy.

Week 3:  During this week of your pregnancy, which is approximately 1 week after conception, the embryo is experiencing extensive phases of basic development.  The four major systems being impacted at this point are the initial development of the heart, the brain, the spinal cord, and the gastrointestinal tract.

Weeks 4 & 5:  During this stage of your pregnancy, which is approximately 2-3 weeks after conception, the heart is now beating with a steady rhythm.  Leg buds and arm buds are visible, but they are not clearly distinguishable at this stage.  The formation of the placenta is occurring, and important hormones, such as hCG, are being produced.  The main vessels of the embryo are receiving a rudimentary supply of blood, and the early structures that will eventually develop into the ears and eyes are beginning to form.  The embryo is approximately ¼ of an inch in length by the end of this stage of the pregnancy.

Week 6:  During this stage of your pregnancy, which is approximately 4 weeks after conception, webbed structures are present on the hand and feet buds that will eventually develop into the fingers and toes.  Other structures that are beginning to develop are the jaw, the nose, the palate, and the lungs.  At this stage, the brain is continuing its development, and the formation of the complex components of the brain has started.  It is possible that an audible heartbeat could be detected through the use of a vaginal ultrasound.  The embryo is approximately ½ of an inch in length by the end of this stage of the pregnancy.

Week 7:  During this stage of your pregnancy, which is approximately 5 weeks after conception, the formation of all of the essential organs of the body has begun, even though the overall embryonic weight is quite small.  This stage is marked by the development of hair and nipple follicles, and the formation of the tongue and eyelids has started.  As the trunk begins to straighten, the toes and elbows become more visible.

Week 8:  During this stage of your pregnancy, which is approximately 6 weeks after conception, the external and internal development of the ears is progressing.  All of the structures of the body of an adult human are now present in the small embryo.  The formation of some of the skeletal structure has begun, and the accompanying muscles can contract.  The various facial features are continuing their maturation, and the eyelids are further developed.  This stage of the pregnancy marks the end of the embryonic period and the beginning of the fetal period.  The embryo is approximately one inch in length by this stage of the pregnancy, and is roughly the size of a bean.

 Weeks 9 - 13:  During this stage of your pregnancy, which is approximately 7-11 weeks after conception, the fetus has grown to approximately 3 inches in length and weighs about one ounce.  Even though the genitalia have clearly formed into female or male, it would not be possible to clearly distinguish them on an ultrasound.  At this stage of the pregnancy, the eyelids have closed, and they will remain closed until approximately Week 28.  The head represents nearly half of the overall size of the fetus, the buds for the development of baby teeth are present, and the fetus can make a fist.

 

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By Jack Rambadt of Expecting Parents Alliance of America




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  • Pregnancy



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