What Might Go Wrong in the Third Trimester?


Weeks 28 through 40 bring the arrival of the third trimester. This exciting time is definitely the home stretch for expectant mothers, but it also presents a time where complications can occur. Just as each trimester can bring its own challenges, so can the third trimester.

Prenatal care is especially important in the third trimester because the types of complications that can arise at this time are more easily managed if detected early. You’ll likely start visiting your obstetrician every other week from 28 to 36 weeks, then once per week until your little one arrives.

Gestational Diabetes

According to the American Diabetes Association, as many as 9.2 percent of pregnant women have gestational diabetes. Gestational diabetes occurs because the hormonal changes of pregnancy make it more difficult for your body to effectively use insulin. When insulin cannot do its job of lowering blood sugar to normal levels, the result is abnormally high glucose (blood sugar) levels. Most women have no symptoms. While this condition is usually not dangerous for the mother, it poses several problems for the fetus. Specifically, macrosomia (excessive growth) of the fetus can increase the likelihood of cesarean delivery and the risk of birth injuries. When glucose levels are well-controlled, macrosomia is less likely.

At the beginning of the third trimester (between weeks 24 and 28), all women should get tested for gestational diabetes. During the glucose tolerance test (also known as the screening glucose challenge test), you will consume a drink that contains a certain amount of glucose (sugar) and at a specified time later your doctor will test your blood sugar levels.

For the oral glucose tolerance test, your blood sugar levels are checked after you have fasted for at least eight hours and you’ve drank 100 mg of glucose. Your blood sugar levels will be measured at one, two, and three hours after drinking the glucose.

The typical expected values are:

  • after fasting: 95 to 105 mg/dL
  • after one hour: 180 to 190 mg/dL
  • after two hours: 155 to 165 mg/dL
  • after three hours: 140 to 145 mg/dL

If two of the three results are too high after drinking the glucose, a woman likely has gestational diabetes.

Gestational diabetes can be treated with lifestyle changes and medicines, in some instances. Your doctor will recommend dietary changes, such as decreasing your carbohydrate intake and increasing fruits and veggies. Adding low-impact exercise can also help. In some instances, your doctor may prescribe insulin.

The good news is that gestational diabetes usually goes away during the postpartum period. However, a woman who has had gestational diabetes has a higher risk of having diabetes later in life compared to a woman who didn’t have gestational diabetes. The condition could also impact a woman’s chances of becoming pregnant again. A doctor will likely recommend checking a woman’s blood sugar levels to make sure they’re under control before she tries to have another baby.


Preeclampsia is a serious condition that makes regular prenatal visits even more important. The condition typically occurs after 20 weeks of pregnancy and can cause serious complications for mom and baby.

According to the Preeclampsia Foundation, between 5 and 8 percent of women experience the condition. Teenagers, women 35 and older, and women pregnant with their first baby are at a higher risk.

Symptoms of the condition include high blood pressure, protein in the urine, and swelling of the hands and feet. Prenatal visits are essential because tests done during these visits can detect symptoms like high blood pressure and increased protein in the urine. If left untreated, preeclampsia can lead to eclampsia (seizures), kidney failure, and, rarely, death in the mother and fetus.

Signs and Symptoms
The first sign that your doctor usually sees is high blood pressure during a routine prenatal visit. Also, protein may be detected in your urine during a urinalysis. Some women may gain more weight than expected. Others experience headaches, vision changes, and upper abdominal pain.

Women should never ignore symptoms of preeclampsia. You should seek emergency medical treatment if you have rapid swelling in the feet and legs, hands, or face. Other emergency symptoms include:

  • headache that does not go away with medication
  • loss of vision
  • “floaters” in your vision
  • severe pain on your right side or in your stomach area
  • easy bruising

These signs may suggest severe preeclampsia. Blood tests, such as liver and kidney function tests and blood clotting tests, may confirm the diagnosis and can detect severe disease.


How your doctor treats preeclampsia depends on its severity and how far along in the pregnancy you are. Delivering your baby may be necessary to protect you and your little one. Your doctor will discuss several considerations with you.

  • If your baby is at term (39 weeks or greater) or preterm (37 to 39 weeks), your doctor may likely recommend inducing labor. At this stage, the risks to you and your baby often outweigh the benefits of continuing the pregnancy.
  • If your baby is 34 to 37 weeks, your doctor will consider how severe your condition is. Your doctor will monitor you closely and test your blood and urine to make sure your condition isn’t getting worse. If it is, your doctor may deliver your baby.
  • If your baby is younger than 34 weeks, you will probably take medication to speed up the baby’s lung development. You may have to stay at the hospital for observation and to manage your blood pressure until the baby is old enough for delivery.

Preeclampsia typically disappears after delivery. However, sometimes blood pressure medication will be prescribed for a short time after delivery. Diuretics may be prescribed to treat pulmonary edema (fluid in the lungs). Magnesium sulfate given before, during, and after the delivery can help to reduce seizure risks.

According to the Mayo Clinic, if you’ve had preeclampsia, you’re at greater risk for having the condition with future pregnancies. Always talk with your doctor about how you can lower your risk.

Cause and Prevention

Despite years of scientific study, the true cause of preeclampsia is not known, nor is there any effective prevention. The cure, however, has been known for many decades, and that is delivery of the baby. Timely diagnosis and delivery is the best way to avoid serious problems for mother and baby.

Preterm Labor

According to the American College of Obstetricians and Gynecologists, preterm labor occurs when you start having contractions that cause cervical changes before you’re 37 weeks pregnant.

Some women are at greater risk for preterm labor, including those who:

  • are pregnant with multiples (twins or more)
  • have an infection of the amniotic sac (amnionitis)
  • have excess amniotic fluid (polyhydramnios)
  • have had a previous preterm birth


Signs and symptoms of preterm labor can be subtle. An expectant mom may pass them off as part of pregnancy. Symptoms include:

  • diarrhea
  • frequent urination
  • lower back pain
  • tightness in the lower abdomen
  • vaginal discharge
  • vaginal pressure

Of course, some women may experience more severe labor symptoms. These include regular, painful contractions, leaking of fluid from the vagina, or vaginal bleeding.


Infants born prematurely are at risk for health problems because their bodies haven’t had time to fully develop. One of the greatest concerns is lung development because the lungs develop well into the third trimester. The younger a baby is when they are born, the greater the complications.

Doctors don’t know the exact cause of premature labor. However, it’s important for you to receive care as soon as possible. Sometimes medicines like magnesium sulfate can help stop preterm labor and delay delivery. Each day your pregnancy is prolonged increases your chances for a healthy baby.

Doctors often give a steroid medication to moms whose preterm labor starts before 34 weeks. This helps mature your baby’s lungs and reduces the severity of lung disease if your labor cannot be stopped. This medication has its peak effect within two days, so it’s best to prevent delivery for at least two days, if possible.

All women with preterm labor who haven’t been tested for the presence of group B streptococcus should receive antibiotics (penicillin G, ampicillin, or an alternative for those who are allergic to penicillin) until delivery.

If preterm labor begins after 36 weeks, the baby is usually delivered, since the risk of lung disease from prematurity is very low.

Preterm Premature Rupture of Membranes (PPROM)

Rupture of membranes is a normal part of giving birth. It’s the medical term for saying your water broke. This means that the amniotic sac that surrounds your baby has broken, allowing the amniotic fluid to flow out.

While it’s normal for the sac to break during labor, if it happens too early it can cause serious complications. This is called preterm premature rupture of membranes (PPROM). Although the cause of PPROM isn’t always clear, sometimes an infection of the amniotic membranes is the cause.


Treatment for PPROM varies. Women are often hospitalized and given antibiotics, steroids, and drugs to stop labor (tocolytics). When PPROM occurs at 34 weeks or more, some doctors recommend inducing labor. At that time, the risks of prematurity are less than the infection risks. If there are signs of infection, labor must be induced to avoid serious complications.

According to the American Family Physician, women who experience PPROM before 24 weeks’ gestation usually deliver their babies within a week of their membranes rupturing. Occasionally, a woman with PPROM experiences resealing of the membranes. In these rare cases, she may continue her pregnancy to near term. She’ll still need close observation.

Risks of prematurity decrease significantly as the fetus nears term. If PPROM occurs in the 32 to 34 week range and the remaining amniotic fluid shows that the fetus' lungs have matured enough, some physicians induce labor. With improved intensive care nursery services, many preterm infants born in the third trimester (after 28 weeks) do very well.

Problems with the Placenta (Previa and Abruption)

Bleeding in the third trimester may have several causes. The more serious causes are placenta previa and placental abruption.

Placenta Previa

The placenta is the organ that nourishes your baby while you’re pregnant. Usually, the placenta is delivered after your baby. However, women with placenta previa have a placenta that comes first and blocks the opening to the cervix.

Doctors don’t know the exact cause of this condition. Women who’ve had a previous cesarean delivery or uterine surgery are at greater risk. Women who smoke or have a larger-than-normal placenta are also at greater risk. Placenta previa increases risk of bleeding before and during delivery. This can be life-threatening.

A common symptom of placenta previa is bright red, sudden, profuse, and painless vaginal bleeding, which usually occurs after the 28th week of pregnancy. Doctors usually use an ultrasound to identify placenta previa.

Treatment depends on whether the fetus is preterm and the amount of bleeding. If labor is unstoppable, the baby is in distress, or there is life-threatening hemorrhage, immediate cesarean delivery is indicated no matter the fetus’ age.

If the bleeding stops or isn’t too heavy, delivery can often be avoided. This allows more time for the fetus to grow if the fetus is near-term; a doctor usually recommends cesarean delivery. Thanks to modern obstetric care, ultrasound diagnosis, and the availability of blood transfusion, if needed, women with placenta previa and their infants usually do well.

Placental Abruption

Placental abruption is a condition in which the placenta separates from the uterus prior to labor. According to UpToDate, placental abruption occurs in 0.3 to 1 percent of pregnancies. Placental abruption can result in fetal death and can cause serious bleeding and shock in the mother.

Risk factors for placental abruption include:

  • advanced maternal age
  • cocaine use
  • diabetes
  • heavy alcohol use
  • high blood pressure
  • pregnancy with multiples
  • preterm premature rupture of the membranes
  • prior pregnancies
  • short umbilical cord
  • smoking
  • trauma to the stomach
  • uterine distention due to excess amniotic fluid

Placental abruption doesn’t always cause symptoms. But some women experience heavy vaginal bleeding, severe stomach pain, and strong contractions.

A doctor can evaluate a woman’s symptoms and the baby’s heartbeat to identify potential fetal distress. In many instances, rapid cesarean delivery is often necessary. If a woman loses excess blood, she may also need a blood transfusion.

Intrauterine Growth Restriction (IUGR)

Occasionally a baby won’t grow as much as they’re expected to at a certain stage in a woman’s pregnancy. This is known as intrauterine growth restriction (IUGR). Not all small babies have IUGR — sometimes their size can be attributed to the smaller size of their parents.

IUGR can result in symmetrical or asymmetrical growth. Babies with asymmetrical growth often have a normal-sized head with a smaller-sized body.

  • Maternal factors that can lead to IUGR include:
  • anemia
  • chronic renal disease
  • placenta previa
  • placental infarction
  • severe diabetes
  • severe malnutrition

Fetuses with IUGR may be less able to tolerate the stress of labor than infants of normal size. IUGR babies also tend to have less body fat and more trouble maintaining their body temperature and glucose levels (blood sugar) after birth.

If growth problems are suspected, a doctor can use an ultrasound to measure the fetus and calculate an estimated fetal weight. The estimate can be compared with the range of normal weights for fetuses of similar age. In order to determine whether the fetus is small for gestational age or growth restricted, a series of ultrasounds will be done over to time to document weight gain or lack thereof.

A specialized ultrasound monitoring umbilical blood flow can also determine IUGR. Amniocentesis may be used to check for chromosomal problems or infection. Monitoring the fetal heart pattern and measurement of the amniotic fluid are common.

If a baby stops growing in the womb, a doctor may recommend induction or cesarean delivery. Luckily, most growth-restricted babies develop normally after birth. They tend to catch up in growth by 2 years old.

Post-Term Pregnancy

According to UpToDate, about 10 percent of women deliver after 42 weeks. Doctors consider this post-term or post-dates. The cause of post-term pregnancy is unclear, although hormonal and hereditary factors are suspected.

Sometimes, a woman's due date isn’t calculated correctly. Some women have irregular or long menstrual cycles that make ovulation harder to predict. Early in pregnancy, an ultrasound can help to confirm or adjust the due date.

Post-term pregnancy is not generally dangerous to the mother's health. The concern is for the fetus. The placenta is an organ that is designed to work for about 40 weeks. It provides oxygen and nutrition for the growing fetus. After 41 weeks of pregnancy, the placenta is less likely to work well, and this may result in decreased amniotic fluid around the fetus (oligohydramnios). This condition can cause compression of the umbilical cord and decrease oxygen supply to the fetus. This may be reflected on the fetal heart monitor in a pattern called late decelerations. There is a risk of sudden fetal death when the pregnancy is post-term.

Once a woman reaches 41 weeks of pregnancy, she usually has fetal heart rate monitoring and a measurement of the amniotic fluid. If the testing shows low fluid levels or abnormal fetal heart rate patterns, labor is induced. Otherwise, spontaneous labor is awaited until no more than 42 to 43 weeks, after which it’s induced.

The other risk is meconium. Meconium is a fetus' bowel movement. It’s more common when the pregnancy is post-term. Most fetuses that have a bowel movement inside the uterus have no problems. However, a stressed fetus can inhale the meconium, causing a very serious type of pneumonia and rarely, death. For these reasons, doctors will work to clear a baby’s airway as much as possible if a baby’s amniotic fluid is meconium-stained.

Malpresentation (Breech, Transverse Lie)

As a woman approaches her ninth month of pregnancy, the fetus generally settles into a head-down position inside the uterus. This is known as vertex or cephalic presentation. According to the World Health Organization, the fetus will be bottom or feet first, known as breech presentation in about 3 percent of pregnancies. Occasionally, the fetus will be lying sideways (transverse presentation).

The safest way for a baby to be born is head first or in the vertex presentation. If the fetus is breech or transverse, the best way to avoid problems with delivery and prevent cesarean is to try to turn (or vert) the fetus to vertex presentation (head down). This is known as external cephalic version. It’s usually attempted at 37 to 38 weeks if the malpresentation is known.

External cephalic version is somewhat like a firm massage of the abdomen and can be uncomfortable. It’s usually a safe procedure, but some rare complications include placental abruption and fetal distress, necessitating emergency cesarean delivery.

If the fetus is successfully turned, spontaneous labor can be awaited or labor can be induced. If it’s unsuccessful, some doctors wait a week and try again. If unsuccessful after reattempts, you and your doctor will decide the best type of delivery, vaginal or cesarean. Breech fetuses can be delivered vaginally or by cesarean. Measurement of the bones of the mother's birth canal and ultrasound to estimate fetal weight are often obtained in preparation for breech vaginal deliveries. Transverse fetuses are delivered by cesarean.

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