Robert Wood Johnson University Hospital

First Trimester

Pregnancy - The First Trimester

The first prenatal visit:

The first prenatal visit is the most thorough. A complete medical history is taken, a physical examination is conducted, as well as certain tests and procedures are performed to assess the initial health of the mother and her unborn baby. The first prenatal visit may include the following:

The first prenatal visit is also an opportunity to ask any questions or discuss any concerns that you may have about your pregnancy.

What to expect during the first trimester:

A healthy first trimester is crucial to the normal development of the fetus. The mother-to-be may not be showing much on the outside, but inside her body all the major body organs and systems of the fetus are forming.

As the embryo implants itself into the uterine wall, several developments take place, including:

It is during this first trimester that the fetus is most susceptible to damage from substances such as alcohol, drugs, certain medications, and illnesses such as rubella (German measles).

During the first trimester, both the mother's body and the fetus are changing rapidly.

Illustration demonstrating fetal growth from 8 to 40 weeks
Click Image to Enlarge

Fetal development during the first trimester:

The most dramatic changes and development occur during the first trimester. During the first eight weeks, a fetus is called an embryo. The embryo develops rapidly and by the end of the first trimester it becomes a fetus that is fully formed, weighing approximately 1/2 to one ounce and measuring, on average, three to four inches in length.

First trimester growth and development benchmarks:

Just as each child grows and matures at different rates and at different times, so does that same child as it begins its life in the womb. The chart provided below provides benchmarks for most normal pregnancies. However, each fetus develops differently.

by the end of 4 weeks
  • all major systems and organs begin to form
  • the embryo looks like a tadpole
  • the neural tube (which becomes the brain and spinal cord), the digestive system, and the heart and circulatory system begin to form
  • the beginnings of the eyes and ears are developing
  • tiny limb buds appear (which will develop into arms and legs)
  • the heart is beating
by the end of 8 weeks
  • all major body systems continue to develop and function, including the circulatory, nervous, digestive, and urinary systems
  • the embryo is taking on a human shape, although the head is larger in proportion to the rest of the body
  • the mouth is developing tooth buds (which will become baby teeth)
  • the eyes, nose, mouth, and ears are becoming more distinct
  • the arms and legs are clearly visible
  • the fingers and toes are still webbed but can be clearly distinguished
  • the main organs continue to develop and you can hear the baby's heartbeat using an instrument called a Doppler
  • the bones begin to develop and the nose and jaws are rapidly developing
  • the embryo is in constant motion but cannot be felt by the mother
from embryo to fetus After 8 weeks, the embryo is now referred to as a fetus (which means offspring).

Although the fetus is only 1 to 1 1/2 inches long at this point, all major organs and systems have been formed.

during weeks 9-12
  • the external genital organs are developed
  • fingernails and toenails appear
  • eyelids are formed
  • fetal movement increases
  • the arms and legs are fully formed
  • the voice box (larynx) begins to form in the trachea

The fetus is most vulnerable during the first 12 weeks. During this period of time, all of the major organs and body systems are forming and can be damaged if the fetus is exposed to drugs, German measles, radiation, tobacco, and chemical and toxic substances.

Even though the organs and body systems are fully formed by the end of 12 weeks, the fetus cannot survive independently.

Changes in the mother's body:

During pregnancy, many changes are also occurring in the mother-to-be's body. Women experience these changes differently. Some symptoms of pregnancy continue for several weeks or months, while others are only experienced for a short period of time. Some women experience many symptoms, while other women experience only a few or none at all. The following is a list of changes and symptoms that may occur during the first trimester:

What are Kegel exercises?

Kegel exercises are pelvic floor exercises that help tone the muscles in the vagina and perineum, which is important for delivery. Conditioned muscles will make the birthing process easier. In addition, these exercises, when done after delivery, can help to speed up the recovery process. Doing a Kegel exercise is simple.

Tighten the muscles around your vagina and anus. (The exercise is similar to stopping urination midstream.)

Hold the muscles tightened as long as you can, working up to 8 to 10 seconds each time.

Relax the muscles.

Tighten and relax the muscles several times a day.

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Online Resources of Pregnancy, Birth, and Baby Center


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