The First Trimester

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The first 12 weeks after the first day of the last menstrual cycle is commonly referred to as the First Trimester of a pregnancy.  This stage of the pregnancy tends to be one of the most consuming timeframes for most women because it can be simultaneously exciting. new, and sometimes overwhelming!  The first trimester also marks an amazing developmental period for the baby!  The following is a listing of some of the basic information that you should keep in mind regarding the first trimester of your pregnancy: 

Fetal Development: 

•    Fertilization:  Approximately 2 weeks after the beginning of the last menstrual period, an egg will be released by the mother’s body, which will be subsequently fertilized by a sperm.  At this point, the fertilized egg will contain the necessary forty-six chromosomes that are required to determine the hair color, the height, and the sex of the baby.  The fertilized egg will start to divide, and to start its progression to the uterus through the fallopian tubes of the mother.

•    Implantation:  Approximately 5-7 days after fertilization occurs, the egg will attach itself to the lining of the uterus.  At this stage of the pregnancy, the fertilized egg will begin to grow at a rapid pace, effectively doubling in size every day.  This stage of the pregnancy also entails the development of the placenta and the umbilical cord.  The umbilical cord will provide oxygen and nourishment to the baby, while at the same time removing waste products.

•    Week 4 (two weeks after conception):  At this stage of the pregnancy, the mother will most likely miss her expected period.  The size of the embryo is approximately 1/100 of an inch, however, the spinal cord is present and tissues are dividing into three distinct layers that will eventually help to form the different systems and organs in the baby’s body.

•    Week 6 (four weeks after conception):  At this stage of the pregnancy, the embryo is now approximately 1/6 of an inch in length, and the limb buds, which will ultimately develop into the arms and legs, have become apparent.  A heartbeat can now be detected on an ultrasound, as blood is actively being pumped through the fetal circulatory system.

•    Month 2:  At this stage of the pregnancy, the baby is now approximately 1/2 of an inch in length, and weighs a mere fraction of an ounce.  The second month of the pregnancy is highlighted by rapid fetal development.  All of the major systems and organs of the baby will have started to develop by the end of the second month.  By the end of this month of the pregnancy, the baby will start to look like a very tiny human infant.  It will be a little over one inch in length, but still weighs less than one ounce.

•    Month 3:  At this stage of the pregnancy, the baby is now officially referred to as a fetus, as it will be fully formed by the end of the month.  Movement of the baby’s hands and legs is occurring, and the mouth is opening and closing, however, these movements tend to be slight, and the baby is too small for the movements to be felt by the mother.  Hair is beginning to form on top of the baby’s head, and the fingers and toes have started to develop.  By the end of this month of the pregnancy the baby will be approximately four inches in length, and will weigh a little over one ounce.

The Mother’s Body: 

•    Pregnancy Symptoms:  A woman starts to experience the first common symptoms of pregnancy at approximately the same time that she misses her expected period.  These symptoms typically include the following:  vomiting and nausea, bouts of dizziness, headaches, enlargement and increased sensitivity in the breasts, frequent urination, heartburn, and both cravings and aversions to particular food items.  These symptoms are often more severe during the first trimester of the pregnancy, and result from hormonal changes that occur in the woman’s body during pregnancy. The most common symptom of the first trimester is nausea and vomiting, which is referred to as “morning sickness.”  The degree of severity of the nausea can range from mild to severe, however, it typically decreases by the end of the first trimester.

•    Emotional Changes:  As noted previously, during the first trimester, the woman is experiencing significant hormonal changes, which can simultaneously impact her emotional state.  These emotional changes can result in irritability, mood swings, and being quick to cry.  The entire concept of pregnancy, whether unplanned or planned, can give rise to various emotions, such as joy and fear, or apprehension and excitement.

•    Physical Changes: During the first trimester, the primary physical changes tend to be most notable in the breasts, as opposed to the belly.  From very early on in the pregnancy, changes are occurring in the breasts as they are developing the capability of producing milk.  A tightening of the bra is one of the first things that a woman tends to notice, whereas most women do not start markedly showing in the belly until the second trimester, typically around Month 4.

•    Weight Gain:  Weight gain during the first trimester of a pregnancy can vary markedly from one woman to another.  On average, a woman gains approximately five pounds during the first trimester, however, some women actually lose weight from the nausea and vomiting that they experience (morning sickness).

Doctor Visits: 

•    When to See the Doctor:  It is highly recommended that women notify their physician as soon as they suspect that they may be pregnant.  Typically, it is expected that the first appointment with the doctor should occur within a timeframe of twelve weeks after the end of the last menstrual cycle.  The aforementioned timeframe can change, however, under certain circumstances:  women over the age of 35, women with pregnancies that are considered high-risk, or teenage women.  Under these circumstances, it is highly recommended that the first appointment with the physician occur earlier, as the women may require more intensive support.  Typically, doctor visits should occur every four to six weeks during the first trimester of a pregnancy

•    The First Prenatal Appointment:  The first prenatal visit typically occurs between 8 and 12 weeks, and it is often the longest.  During this visit, the doctor will inquire about your medical history, with a particular focus on previous obstetrical visits and whether or not there is any history of prenatal problems in the family.  Typically, the doctor will attempt to determine the due date.  This is done by either conducting an ultrasound examination or by making a calculation based on the first day of the woman’s last menstrual cycle. 
The woman should expect a relatively thorough physical during this appointment, which will include a urine test, blood pressure reading, pelvic exam, and pap smear.  The doctor will also conduct some routine blood tests, which will be used to determine Rh factor and blood type, as well as to look for the presence of sexually transmitted diseases.  During the first prenatal appointment, the doctor will prescribe a prenatal vitamin, as it is important that the mother and baby receive adequate amounts of the critical vitamins and minerals that contribute to healthy growth and development.  These include folic acid, calcium, and iron.

•    Prenatal Appointment Week 9-12:  Several things are typically measured and recorded during the prenatal appointments, such as blood pressure, the size of the uterus, a test for the presence of either protein or glucose in the urine, the weight of the patient, and the fetal heart rate.  These appointments represent the perfect opportunity for the woman to ask the doctor questions regarding expected symptoms, a proper diet, appropriate exercise, and what should be expected to happen next.  Should it be necessary to take a sampling of chorionic villi, this will often occur during week 8 and week 12 of the pregnancy.

Problems to Watch Out For: 

•    Bleeding:  There may be several reasons why a woman would experience bleeding during the first trimester of a pregnancy.  Please bear in mind that bleeding does not necessarily mean that a miscarriage will occur.  In truth, approximately half of the women who experience bleeding during the first trimester do not have miscarriages.  Bleeding during pregnancy, however, should never be considered normal, and your health care provider should be contacted.  Typically, slight bleeding will stop without medical intervention, however, a doctor will often want to run various tests to try to determine the specific cause of the bleeding.  Should the bleeding be heavy, and be accompanied by either fever, cramping, pain, or weakness, medical attention should be immediately sought.

•    Miscarriage:  Approximately one out of six pregnancies will end in miscarriage, which will often occur during the first 12 weeks.  There are many times when the woman will feel responsible for the miscarriage, but no evidence exists to support that physical activity, sexual activity, or emotional stress can cause a miscarriage.   Typically, there is nothing that can be done to prevent a miscarriage from occurring once the process has started.  Common indicators of miscarriage can be vaginal bleeding, cramping pain in the lower abdomen that tends to be more severe than menstrual cramps, or the passage of tissue through the vagina.  It is highly recommended that a woman be examined by a physician should any of the aforementioned occur, so that a miscarriage can be confirmed and the doctor can assure that it is complete.

•    Ectopic Pregnancy:  If the fetus fails to properly implant itself in the uterus, and instead begins to develop within the fallopian tube, it is referred to as an ectopic pregnancy.  This is a very dangerous circumstance, and can even be life-threatening should the fallopian tube rupture.  The common symptoms of an ectopic pregnancy are sharp abdominal cramping or localized cramping on one side of the abdomen.  Ectopic pregnancies are not as common as miscarriages, and occur in approximately one out of sixty pregnancies.  The risk of ectopic pregnancy increases in women who have either experienced one previously, or who have sustained an infection in the fallopian tubes, such as pelvic inflammatory disease.


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By Jack Rambadt of Expecting Parents Alliance of America

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