First Trimester

The First Trimester

The first prenatal visit

The first prenatal visit is the
most thorough. A healthcare provider asks the mother-to-be about her health history
and
does a physical exam. Certain tests and procedures are also done to check the initial
health of the mother and her unborn baby. The first prenatal visit may include:

  • Personal health history. This may cover:

    • Past and current health
      conditions, like diabetes, high blood pressure (hypertension), anemia, and
      allergies

    • Current medicines
      (prescription and over-the-counter)

    • Past surgeries

  • Maternal and paternal family health history. The
    healthcare provider will ask about illnesses such as diabetes or intellectual or
    developmental disabilities. He or she will also ask about genetic disorders, like
    sickle-cell disease or Tay-Sachs disease.

  • Personal gynecological and obstetrical history. The
    healthcare provider will want to know about past pregnancies (stillbirths,
    miscarriage, deliveries, terminations) and menstrual history (length and duration
    of menstrual periods).

  • Education. The healthcare provider will talk with the
    pregnant woman about the importance of eating a healthy diet, exercising
    regularly, and not using alcohol, illegal drugs, and tobacco. He or she will also
    cover any concerns about domestic violence.

  • Pelvic exam. This exam may be done for 1 or all these
    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 find the presence of abnormal cells

  • Lab tests. These may include:

    • Urine tests. These are done to screen for
      bacteria, sugar, and protein.

    • Blood tests. These are done 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. Rh incompatibility happens when the mother’s
      blood is Rh-negative and the father’s blood is Rh-positive and the fetus’
      blood is Rh-positive. The mother may make antibodies against the Rh-positive
      fetus, which may lead to anemia in the fetus. Incompatibility problems are
      closely watched. Treatment is available to prevent the formation of Rh
      antibodies during pregnancy.

  • Blood screening tests. These are done to find
    diseases, like rubella. This infectious disease is also called German measles.

  • Genetic tests. These are done to find inherited
    diseases, like sickle-cell anemia and Tay-Sachs disease.

  • Screening tests. These are done to find infectious
    diseases, like sexually transmitted infections (STIs).

The first prenatal visit is also a
good time for the mother-to-be to ask any questions or talk about any pregnancy
concerns.

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:

  • Amniotic sac. A sac filled with amniotic fluid
    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. It also helps to regulate the temperature of
    the fetus.

  • Placenta. 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.

  • Umbilical cord. The umbilical cord is a rope-like cord
    connecting the fetus to the placenta. The umbilical cord contains 2 arteries and a
    vein. These 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 prone to damage from substances like alcohol, illegal drugs,
certain medicines, and illnesses, such as rubella.

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


Illustration demonstrating fetal growth from 8 to 40 weeks

Fetal development during the first
trimester

The most dramatic changes and
development happen during the first trimester. During the first 8 weeks, a fetus is
called an embryo. The embryo develops rapidly. By the end of the first trimester,
it
becomes a fetus that is fully formed. The fetus weighs about 1/2 to 1 ounce and
measures, on average, 3 to 4 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 below provides benchmarks for most normal pregnancies.
But 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. But 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 can be easily seen.

  • The fingers
    and toes are still webbed but can be clearly distinguished.

  • The main
    organs continue to develop. 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 to 12
  • The external
    genital organs are developed.

  • Fingernails
    and toenails appear.

  • Eyelids are
    formed.

  • The fetus
    starts to move more.

  • 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 time, all the major
organs and body systems are forming. They can be damaged if the fetus is
exposed to drugs, rubella, 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 happening in the body of the mother-to-be. Women experience these changes
differently. Some symptoms of pregnancy continue for several weeks or months. Others
are
only experienced for a short time. Some women have many symptoms. Other women have
only
a few or none at all. Here is a list of changes and symptoms that may happen 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 and darken. They may
    become covered with small, white bumps. These are called Montgomery tubercles
    (enlarged sweat glands).

  • Veins become more noticeable
    on the surface of the breasts.

  • The uterus is growing and
    begins to press on the woman’s bladder. She may need to urinate more often.

  • Partly due to surges in
    hormones, a pregnant woman may have mood swings much like premenstrual syndrome
    (PMS). Women with PMS may have mood swings, irritability, and other physical
    symptoms that happen shortly before each menstrual period.

  • Increased levels of hormones
    to sustain the pregnancy may cause “morning sickness.” This is feelings of nausea
    and sometimes vomiting. Morning sickness does not necessarily happen just in the
    morning. And it rarely interferes with proper nutrition for the mother and her
    fetus.

  • Constipation may happen as
    the growing uterus presses on the rectum and intestines.

  • 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 stomach increases for the growing
    fetus.

  • A woman may be extremely
    tired due to the physical and emotional demands of pregnancy.

  • Cardiac volume increases
    by about 40% to 50% from the start to the end of the pregnancy. It causes an
    increased cardiac output. An increased cardiac output may cause an increased pulse
    rate during pregnancy. The increase in blood volume is needed for extra blood flow
    to the uterus.