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Fetal Development in the First Trimester

Seeing a positive pregnancy test can come with a lot of emotions and may sometimes be hard to believe. What exactly is happening inside your body during those early days when you may feel tired and nauseous but don’t yet see a baby bump or feel movement? Learning about some of the strides your body and baby are making in the first trimester can help you gain confidence as you navigate pregnancy and discuss it with your healthcare team.


What defines the first trimester?


The first trimester spans the time between your last menstrual period (LMP) and the end of the 12th week [1]. During the first 2 weeks of pregnancy, conception has not yet happened.


However, this time is still important as your body and hormones are setting the stage for a potential pregnancy. If conception occurs during ovulation (around 2 weeks after your LMP), a fertilized egg then makes its way to your uterus for implantation where it will soon form an embryo and the placenta [2].


From Embryo to Fetus


During weeks 3 to 8, the pregnancy is in its embryonic stage [2]. This is the time when some of the major organs begin to develop. This is also around the time when you may start to feel symptoms of pregnancy as your hormones are working extra hard to support the growing embryo. At week 9, the embryo becomes a fetus and is called this during the rest of the pregnancy. During this time, more specific characteristics like hair and sex are established as the rest of the body grows.


Developments Week by Week


Below is listed some of the most prominent characteristics of the fetus that develop each week after implantation has occurred [1]:

  • Week 5: The embryo is made up of 3 layers called the ectoderm, mesoderm, and endoderm. These layers are the basis for the rest of the organs that will soon take shape.

  • Week 6: The neural tube, the foundation for the brain and spinal cord, closes along the embryo’s back. Buds, which will later become arms, form on the sides of the embryo. By vaginal ultrasound, a pulse from the cells that eventually make up the heart can be found [2].

  • Week 7: The face becomes more pronounced as the early stages of the nose and eyes are forming [1]. The buds for the legs also appear this week.

  • Week 8: Fingers, the upper lip, and parts of the ears are now developing. While still hunched over, some straightening of the embryo’s torso occurs.

  • Week 9: The arms have grown long enough for elbows to form, and toes are now present on the fetus’ feet. A heartbeat may be detected with a Doppler ultrasound during this week [2].

  • Week 10: While it has been present, the umbilical cord can now be clearly seen [1]. The webbing on fingers and toes disappear to allow for some wiggling.

  • Week 11: More of the internal organs develop this week as the liver starts to house red blood cells. The external genitalia starts to form. Buds that will become teeth are now seen. The eyes and ears have more detail now too.

  • Week 12: The fetus’ intestines are now in place and functioning. The fetus’ urinary system is also functioning as it drinks and pees amniotic fluid [2]. Fingernails are starting to develop, and the fetus’ facial profile is more pronounced at this point [1].


What This Means for You


It’s no wonder if you are feeling the effects of all these bodily changes happening simultaneously. It is important to allow yourself the time and space to both physically rest and emotionally process everything you are experiencing. Some of the symptoms you may have during the first trimester include breast tenderness, appetite changes, frequent urination, heartburn, constipation, fatigue, and nausea/vomiting [3]. While these symptoms can be frustrating, there are tools available to help alleviate them. Discuss with your healthcare provider which medications and methods are safe during pregnancy. The stress that your body is under as well as fear concerning pregnancy and the future can all take a big emotional toll. It is normal to feel overwhelmed, anxious, or sad. Your healthcare team can be with you every step of the way to provide a safe place where you can voice your concerns and navigate your feelings.


Free Pregnancy Services in Central Georgia

There is a lot happening inside your body during the first trimester, and we realize that learning any new information can cause you to have questions. At CORE Healthcare for Women of Central Georgia, our staff is equipped with services and resources to help answer your questions and give you quality care.

  • Our services are free and confidential. Explore our website to see more of what we have to offer.

  • You can schedule an appointment online or call us at (478) 333-5000 today.


Sources


  1. Fetal development: The 1st trimester. Mayo Clinic. (2022, June 3). https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/prenatal-care/art- 20045302

  2. Fetal Development: Week-by-Week Stages of Pregnancy. Cleveland Clinic. (2024, March 19). https://my.clevelandclinic.org/health/articles/7247-fetal-development-stages-of-growth

  3. 1st trimester pregnancy: What to expect. Mayo Clinic. (2024, February 27). https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/pregnancy/art-20 047208

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