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The size and position of the growing fetus can make it impossible for some women to feel comfortable. At this point, a woman is entering the final stretch of pregnancy and may be tired and ready to have it all end.

The last phase of pregnancy is called the “third trimester,” which can be very emotionally and physically challenging for an expectant mother.

For many first-time pregnancies, it is common for a woman to deliver earlier or later than an estimated due date.  It is not uncommon at all for a due date to come and go in an uneventful way, this can be both frustrating and disappointing for women who are marking down the time and waiting excitedly for delivery day.

What Does the Third Trimester Mean for an Expectant Mother?

The third trimester marks the ending of the long and arduous journey of pregnancy, as the expectant mother is busy preparing for the impending birth. As the fetus continues to grow, gaining weight and length, the body systems finish developing and maturing. If not experienced before, by now most women report feeling very uncomfortable as a result of weight gain and the pressure of an enlarged uterus.

During the third trimester, many women develop a birthing plan and begin taking childbirth education classes.  If a woman plans on breastfeeding after birth (which we recommend!), now is an ideal time to take breastfeeding classes as well. In the third trimester, both the mother and developing fetus continue growing and changing.

The following list identifies the most common changes and symptoms woman experiences during the third trimester [1]:

  • An increase in skin temperature because the fetus radiates body heat which can cause the mother to feel warm and flushed.
  • An increase in urinary urgency due to increased pressure placed on the bladder as the fetus drops into the lower pelvic region.
  • Maternal blood pressure may decrease because the developing fetus presses on the main vein that returns blood to the heart.
  • Edema in the face, feet, hands, ankles because of maternal fluid retention.
  • Maternal hair growth on arms, legs, and face due to an increase of hormone stimulation of hair follicles.  Hair texture may also be courser.
  • Frequent leg cramping is common.
  • Braxton-Hicks contractions (false labor) may start at irregular intervals as the uterus prepares for childbirth.
  • Stretch marks may occur on the abdomen, breasts, thighs, and buttocks.
  • Persistent dry, itchy skin may occur, particularly in the abdomial area because the skin is growing and stretching.
  • Colostrum (nutrient-rich fluid which will provide nourishment to the baby until breast milk arrives) may start to leak from the breasts.
  • Maternal sex drive may decrease.
  • Maternal skin pigmentation may become more obvious, particularly darkened patches appearing on the face.
  • Heartburn, constipation, and indigestion might continue.
  • An increase in leukorrhea (white vaginal discharge) which might contain more mucus.
  • Hemorrhoids may develop and become more sensitive.
  • Persistent backaches which may increase in intensity.
  • Varicose veins in the legs may develop and become more severe.

Fetal Development: Weeks 29-40

During the third trimester, the fetus continues growing and developing in both weight and size. The end of the pregnancy is now only a matter of weeks away and the uterus is still a very busy place as the fetus continues developing. The following information outlines fetal development in the last trimester of pregnancy [2]:

Week 29: Fetal movement is forceful, bones are entirely developed, however still soft and pliable. The fetus starts storing iron, calcium, and phosphorus. Eye color has been established, but may change up to six months after birth, particularly if the eyes are blue or blue-gray at birth. The fetus weighs around 2 ½ pounds, and has a length of approximately 15 inches from head to heel.

Week 30: The fetus weighs around 3 pounds, and will gain approximately ½ pound per week until week 37. The fetus practices breathing by moving the diaphragm rhythmically. The lungs and digestive tract are near maturity, almost all major organs are functioning, and weight gain will exceed length growth from now on. 

Week 31: If the fetus is male, the testicles begin to move from the kidneys into the groin on the way to the scrotum. If the fetus is female, the clitoris is now prominent. The lungs are more developed, yet not still fully matured. If born during this week, the fetus may need a ventilator for breathing assistance. Its weight is around 3 ½ pounds and the fetus measures about 16 ½ inches from head to heel.

Week 32: Toenails and fingernails are wholly formed, the fat layer under the skin is thicker, and during this phase, the fetus spends most of the time sleeping. The fetus is running out of room in the cramped uterus, so its movements may seem less forceful. Its weight is approximately 4 pounds and the length is about 17 inches.

Week 33: The fetus is using lungs to practice breathing by inhaling amniotic fluid. The lanugo is now disappearing and being replaced with real body hair. Fingernails now reach the fingertips, the fetus is now drinking and urinating about 1 pint of amniotic fluid per day.  Weight is around 4.4 pounds and length has reached approximately 17 ½ inches.

Week 34: Survival rates for fetuses born at this stage increase, and fat accumulation occurs around the arms and legs. The eyes are opening and closing at regular sleep and awake intervals, and the fingernails have completely formed. The fetus may have turned vertex into the birth canal and the skull bones are formed but still soft to allow for safe passage during delivery. The fetus weighs approximately 5 ¼ pounds and the length is around 18 inches.

Week 35: The fetus is growing rounder and developing more fatty layers, its lungs are almost completely developed and a fetus born at this juncture has a 90% survival rate. The fetus is about 18.5 inches long, and its weight is approximately 5 ½ pounds.

Week 36: Between now and delivery, the fetus will gain about an ounce per day, and the body is becoming chubbier. The fetus gains about a ½ pound per week and the folds of the skin around the neck and wrists are filling out. All of the organs have matured except for the lungs. The fetus weighs about 6 pounds and is approximately 19 inches in length.

Week 37: The fetus is considered full term and is now gaining an ounce per day. He will now begin to develop a daily routine of activity cycles. She is typically around 19 inches from head to heel and weighs around 7 pounds. (Babies born between 37-42 weeks are considered to be full-term after the 42nd week is post-term.)

Week 38: Body fat continues to build, and the wrinkled fetal skin is now becoming smooth. Most babies are born head first and approximately 3% come out showing feet first, while one in eight births is a Cesarean section. The fetus continues to gain weight to be able to regulate body temperature after birth. Some babies are born with a full head of hair while others only have a small amount. The fetus swallows the lanugo and exterior coating which is stored in the bowels and becomes the first bowel movement (meconium). The fetus weighs around 7 ½ pounds and is about 20 inches in length.
 
Week 39: The fetus will continue kicking and punching, but now it will be lower in the abdomen.  Most of the downy hair has disappeared.  It is a good idea for an expectant mother to keep track of fetal movements at this time by doing a “kick count,” which means a mother should count the number of kicks or movements within a specific period. The fetus weighs around 7 ½ pounds and is about 20 inches long.  (Some women experience an urge to “nest,” cook, clean, shop and prepare for the new baby.)

Week 40: All of the body and organ systems are ready to go and fully matured. The fetus weighs approximately 7 ½ pounds and is about 20-21 inches in length and is preparing to be born.

What Does an Expectant Mother Experience During the 3rd Trimester?

During pregnancy, the body of an expectant mother must change both physiological and homeostatic mechanisms to ensure the developing fetus is well provided for. The maternal body must increase blood sugar, breathing and cardiac output are all necessary.

The following is a list of changes an expecting mother will experience in the third trimester:

  • Vaginal bleeding: A bloody show is common when the woman loses the mucus plug (mucous plug covering the cervix) a few days before delivery. This is normal anytime after 36 weeks and could also occur after an internal examination. If the blood is bright red or bleeding is like a menstrual cycle, it is not normal and requires swift medical attention. [3]
  • Contractions can feel like menstrual cramping but longer in duration and may or may not have a pattern. A woman will feel tightening and cramps across the abdomen and maybe in the lower back or down in the front. Cramping can occur when having sexual intercourse, if the bladder is full, or possibly during exercising. It is essential to keep in mind that the contractions of pre-term labor may not be painful. [4]
  • Vaginal Pressure: As the fetal head settles into the birth canal, many expectant women report feeling pressure in the vaginal canal, which is normal and nothing to worry about. If fetal descent occurs earlier, it could be an indication of pre-term labor and should be checked out by a physician. [5]
  • Vaginal discharge: The normal vaginal discharge of pregnancy should be thin, odorless and white. Any smelly, itchy or irritating rash could be a sign of infection and should be checked out by a physician. (A vaginal discharge that is watery and copious could be a sign the amniotic sac has broken, and an expectant mother needs to seek medical attention.) [6]
  • Swelling: Edema is one of the most common side effects of pregnancy, and swelling usually takes place on the face, hands, ankles, and feet. Severe edema in the legs or any puffiness of the hands or face could be a sign of pre-eclampsia (high blood pressure in pregnancy) and needs immediate medical attention. [7
  • Shortness of Breath: The feeling of having to work harder to move air is common during pregnancy. Because of the growing uterus, an expectant mother can easily become exhausted during a long walk or exercise period. The most important concern during pregnancy is that maternal blood is very coagulable and blood clots can quickly travel from the legs or pelvis and move into the lungs and cause an embolism. A severe shortness of breath and rapid breathing requires emergency medical attention. [8]

Maternal Check-up During the 3rd Trimester

During the final trimester of pregnancy, it is normal for an expectant mother to have a once weekly physician appointment. As the due date draws near, a woman can expect a mixture of regular physical examinations, late-term pregnancy tests and discussions about the impending birth. The following list contains some of the things a physician will do at appointments in the third trimester:

  • Ask an expectant mother how she is feeling, address any questions or concerns raised during the last meeting and a review of any test results from the previous visit. A physician will ask an expectant mother about any contractions, swelling, headaches or any other type of complaints.
  • Ask questions about fetal movement and remind an expectant mother to contact the office or health care facility if the fetus seems less active than usual. 
  • Physical examination, weight and blood pressure check, a physician will also take a urine sample to check for pre-eclampsia, urinary tract infection or other conditions. 
  • Face, hands, ankles, and feet will be checked for any swelling.
  • A physician will check fetal heartbeat, manipulate the belly and do a fundal measurement to mark gestational development and track normal growth. (If an infant is too small or too big, an ultrasound could be ordered to evaluate growth and check amniotic fluid levels.)
  • Checking fetus for head down position, if a fetus is in a breech position, an ultrasound may be done to confirm position. If a fetus is not in a head down position, a procedure called an external cephalic version may be done to try and turn the fetus into the right position.
  • If a mother is Rh-negative (Rh is a protein that shows up on the surface of red blood cells), she will receive an injection to ensure the fetus will not experience any problems during pregnancy. 
  • A test for group B strep will be done between 35 and 37 weeks; a physician will swab the vagina and rectum to check for a common infection called group B strep. If a woman tests positive, she will need to take a round of antibiotics during labor to protect the fetus from contracting the infection during delivery.
  • If a woman's blood glucose level was elevated when the challenge test was done, or if a test was not done to determine if the woman has gestational diabetes, the test will be done early in the third trimester.
  • A physician may order a blood test to check for anemia again if a woman was anemic earlier in the pregnancy.
  • If a woman is at risk of a sexually transmitted infection, she will again be tested for syphilis, chlamydia, HIV, and gonorrhea.
  • If the pregnancy is high risk, a physician may order tests to make sure the fetus is thriving.
  • If the pregnancy is healthy and a woman goes past the expected due date, a physician may order a biophysical profile or a modified profile, which includes a non-stress test to measure the fetal heart rate and an ultrasound to check amniotic fluid levels. These types of test are done twice weekly to help the physician determine if the conditions are safe for the pregnancy to continue.

Recommended Weight Gain for a Woman During the 3rd Trimester

It is important for an expectant mother to gain an adequate amount of weight during pregnancy to ensure a healthy birth weight for a baby.  Because maternal weight gain directly influences the size of a baby, an expectant mother should not try to lose weight during pregnancy, unless recommended by her physician. [1,2]

By the third trimester of pregnancy, a woman can expect to have gained anywhere from 25-35 pounds. The amount of weight a woman gains during pregnancy will be directly related to how much she weighed before pregnancy. A woman who is underweight should gain between 28-40 pounds, a woman of normal weight should shoot to gain between 25-35 pounds, a woman who is overweight should strive to gain between 15-25 pounds in total.  During the third trimester, the average weight gain for women is usually around 11 pounds, unless otherwise specified by a physician. [1,2]

(Weight gain for a woman pregnant with twins or multiples will be very different from that of a woman with a singleton pregnancy.  For women expecting more than one infant, consulting and following the guidelines and advice of a healthcare practitioner is always recommended.)

General Facts About the 3rd Trimester

There are some general facts about the third trimester that a woman may or may not experience. Rapid changes are still taking place which can cause a woman to experience a wide range of emotions and fears. Throughout the third trimester, most women will experience the following [1,2]:

  • Shortness of breath: (explained above)
  • Heartburn due to abdominal crowding.
  • Swelling of feet, ankles, face, and hands.
  • Hemorrhoids (inflamed veins of the anus and rectum)
  • Breast tenderness, which may include leaking of colostrum (pre-milk).
  • Belly button may “poke” or stick out.
  • Sleep disturbances from being uncomfortable from a fetus and weight gain.
  • Baby “dropping,” or moving into the lower abdomen in preparation for birth.
  • Contractions (Braxton-Hicks contractions or false labor)

End of the 3rd Trimester

Many important things occur for the mother an infant during the final few weeks of pregnancy. The start of labor feels different for every woman and the strongest indicator that labor has begun are steady and regular contractions. The length of labor will vary from woman to woman and for most first-time mothers the average labor is approximately 12-24 hours. If a woman believes she is in labor, she should contact her physician and the hospital, no matter what time of the day or night.

For many mothers-to-be, the last trimester is both a time of excitement and frustration. It is a waiting game that many women cannot wait to end, feelings can range from euphoria to apprehension. As a sense of anticipation grows, for many women so does a sense of fear about the impending birth. The reality of motherhood may leave a woman feeling sadness, anxiety and for some an overwhelming feeling of calmness and resignation. Stay focused, enjoy the final weeks and revel in the marvels and joy of pregnancy because all too soon, it will be over and the new baby will arrive.