The First Trimester
The first prenatal visit
The first prenatal visit is the most thorough. A complete medical history
is taken, a physical exam is done, and 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:
Personal medical history. This may include taking record of any of the
Previous and current medical conditions, such as diabetes, high blood pressure
(hypertension), anemia, and/or allergies
Current medications (prescription and over-the-counter)
Maternal and paternal family medical history, including illnesses such
as diabetes or intellectual or developmental disabilities, and genetic
disorders, such as sickle cell disease or Tay-Sachs disease.
Personal gynecological and obstetrical history, including past pregnancies
(stillbirths, miscarriage, deliveries, terminations), and menstrual history
(length and duration of menstrual periods).
Education, including a discussion regarding the importance of proper nutrition,
regular exercise, the avoidance of alcohol, drugs, and tobacco during
pregnancy, and a discussion of any concerns about domestic violence.
Pelvic exam. This exam may be done for one or all of the following reasons:
To note the size and position of the uterus
To determine the age of the fetus
To check the pelvic bone size and structure
To perform a Pap test (also called Pap smear) to detect the presence of
Laboratory tests, including the following:
Urine tests, to screen for bacteria, sugar, and protein
Blood tests, to determine blood type
All pregnant women are tested for the Rh factor during the early weeks
of pregnancy. A mother and fetus may have incompatible blood types. The
most common is Rh incompatibility, which occurs when the mother's
blood is Rh-negative, the father's blood is Rh-positive and the fetus'
blood is Rh-positive. The mother may produce antibodies against the Rh-positive
fetus which may lead to anemia in the fetus. Incompatibility problems
are monitored and appropriate medical treatment is available to prevent
the formation of Rh antibodies during pregnancy.
Blood screening tests to detect diseases, such as rubella, an infectious
disease that is also called German measles.
Genetic tests to detect inherited diseases, such as sickle-cell anemia
and Tay-Sachs disease.
Screening tests to detect infectious diseases, such as sexually transmitted diseases.
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:
A sac filled with amniotic fluid, called the amniotic sac, surrounds the
fetus throughout the pregnancy. The amniotic fluid is liquid made by the
fetus and the amnion (the membrane that covers the fetal side of the placenta)
that protects the fetus from injury and helps regulate the temperature
of the fetus.
The placenta is an organ shaped like a flat cake that only grows during
pregnancy. It attaches to the uterine wall with tiny projections called
villi. Fetal blood vessels grow from the umbilical cord into these villi,
exchanging nourishment and waste products with the mother's blood.
The fetal blood vessels are separated from the mother's blood supply
by a thin membrane.
The umbilical cord is a rope-like cord connecting the fetus to the placenta.
The umbilical cord contains two arteries and a vein, which carry oxygen
and nutrients to the fetus and waste products away from the fetus.
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
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 four 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 eight 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 eight weeks, the embryo is now referred to as a fetus (which means
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 nine-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:
The mammary glands enlarge causing the breasts to swell and become tender
in preparation for breastfeeding. This is due to an increased amount of
the hormones estrogen and progesterone. A supportive bra should be worn.
A woman's areolas (the pigmented areas around each breast's nipple)
will enlarge, darken, and may become covered with small, white bumps called
Montgomery's tubercles (enlarged sweat glands).
Veins become more prominent on the surface of the breasts.
The uterus is growing and begins to press on the woman's bladder, causing
the need for her to urinate more frequently.
Partly due to surges in hormones, a pregnant woman may experience mood
swings similar to premenstrual syndrome (a condition experienced by some
women that is characterized by mood swings, irritability, and other physical
symptoms that occur shortly before each menstrual period).
Increased levels of hormones to sustain the pregnancy may cause "morning
sickness," which is feelings of nausea and sometimes vomiting. However,
morning sickness does not necessarily occur just in the morning and rarely
interferes with proper maternal and fetal nutrition.
Constipation may occur as the growing uterus presses on the rectum and
The muscular contractions in the intestines, which help to move food through
the digestive tract, are slowed due to high levels of progesterone. This
may, in turn, cause heartburn, indigestion, constipation, and gas.
Clothes may feel tighter around the breasts and waist, as the size of the
abdomen begins to increase to accommodate the growing fetus.
A woman may experience fatigue due to the physical and emotional demands
Cardiac volume increases by about 40 to 50 percent from the beginning to
the end of the pregnancy, causing an increased cardiac output. This, in
turn, may cause an increased pulse rate during pregnancy. The increase
in blood volume is needed for extra blood flow to the uterus.