The First Trimester of Pregnancy

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:

  • personal medical history - this may include previous and current medical conditions, such as diabetes, high blood pressure (hypertension), anemia, and/or allergies; current medications, such as prescription and over-the-counter; or previous surgeries

  • maternal and paternal family medical history - including illnesses such as diabetes or mental retardation, 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 (i.e., 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 examination - this type of examination may be performed to note the size and position of the uterus; to determine the age of the fetus; to check the pelvic bone size and structure; or to perform a Pap test (also called Pap smear) to detect the presence of abnormal cells.

  • laboratory tests - this includes urine tests (to screen for bacteria, sugar, and protein) and 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. Rh incompatibility occurs 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 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 (i.e., rubella, also called German measles)

  • genetic tests - to detect inherited diseases (i.e., sickle-cell anemia, Tay-Sachs disease)

  • screening tests - to detect infectious diseases (i.e., 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:

  • amniotic sac

    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.

  • 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 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).

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