Fetal Macrosomia – Causes, Complications and Treatment

Definition

Fetal macrosomia is medical condition where a baby is born with more weight and size than usual. In case of this disease, a child might have a birth weight of more than 8 pounds or 4000 grams. About 9 percent of children, worldwide, are born with this syndrome.

The risk factors associated with this disease increases as the weight of the child increases to around 4500 grams. Fetal macrosomia can tend to complicate the chances of vaginal delivery. It can also put the baby in the risk of fatal injury during the birth process. The baby is exposed to increased problems related to health after the birth.

Epidemiology

The prevalence of macrosomia depends on the definition used and the population studied. In the United States in 2014, 6.9% of neonates weighed more than 4000 g, 1% weighed more than 4500 g, and about 0.1% of neonates weighed more than 5000 g.

Risk factors of Fetal Macrosomia

Many factors might increase the risk of fetal macrosomia some you can control, but others you can’t.

For example:

Maternal diabetes: Fetal macrosomia is more likely if you had diabetes before pregnancy (pre-gestational diabetes) or if you develop diabetes during pregnancy (gestational diabetes).

If your diabetes isn’t well controlled, your baby is likely to have larger shoulders and greater amounts of body fat than would a baby whose mother doesn’t have diabetes.

A history of fetal macrosomia: If you’ve previously given birth to a large baby, you’re at increased risk of having another large baby. Also, if you weighed more than 8 pounds, 13 ounces at birth, you’re more likely to have a large baby.

Maternal obesity: Fetal macrosomia is more likely if you’re obese.

Excessive weight gain during pregnancy: Gaining too much weight during pregnancy increases the risk of fetal macrosomia.

Previous pregnancies: The risk of fetal macrosomia increases with each pregnancy. Up to the fifth pregnancy, the average birth weight for each successive pregnancy typically increases by up to about 4 ounces (113 grams).

Having a boy: Male infants typically weigh slightly more than female infants. Most babies who weigh more than 9 pounds, 15 ounces (4,500 grams) are male.

Overdue pregnancy: If your pregnancy continues by more than two weeks past your due date, your baby is at increased risk of fetal macrosomia.

Maternal age: Women older than 35 are more likely to have a baby diagnosed with fetal macrosomia.

Fetal macrosomia is more likely to be a result of maternal diabetes, obesity or weight gain during pregnancy than other causes. If these risk factors aren’t present and fetal macrosomia is suspected, it’s possible that your baby might have a rare medical condition that affects fetal growth.

If a rare medical condition is suspected, your health care provider might recommend prenatal diagnostic tests and perhaps a visit with a genetic counselor, depending on the test results.

Causes of Fetal Macrosomia

Causes for fetal macrosomia include:

  • Pre-existing diabetes
  • History of macrosomia
  • Mother’s pre-pregnancy weight
  • A large increase in maternal weight gain during pregnancy
  • Multiparity
  • A male fetus
  • Gestational period longer than 40 weeks
  • The mother’s weight and height at birth
  • A mother younger than 17 years old

The most serious of these causes is pregestational diabetes and gestational diabetes, which have a high association with fetal macrosomia.

Studies show that women with untreated diabetes have an increased risk of delivering a baby that weighs more than 9 pounds 14 ounces. If gestational diabetes is ignored, the baby’s risk of fetal macrosomia could be as high as 20%.

Causes of Fetal Macrosomia

Symptoms

While there are no specific symptoms of macrosomia, the following are the signs of a big baby during pregnancy:

Excessive Fundal Height: Foetal macrosomia is usually suspected when your routine antenatal (pre-delivery) visits to a doctor are suggestive of excessive fundal height (maximum distance from the pubic bone to the top of the uterus in the abdomen). It is generally termed as being large for gestational age in the medical language.

High Weight Gain: Excessive body weight during later pregnancy might be an indirect symptom of having a macrosomia baby.

Polyhydramnios: Excessive amniotic fluid, which surrounds the uterus and acts as a shock absorber may be associated with this condition. This can be detected by ultrasonography. According to some investigators, polyhydramnios is said to be a result of excessive urine output by a large baby.

Complications of Fetal Macrosomia

Macrosomia can cause complications to both the mother and baby.

Problems with the mother include:

Injury to the vagina: As the baby is delivered, he or she can tear the mother’s vagina or the muscles between the vagina and anus, the perineal muscles.

Bleeding after delivery: A large baby can prevent the muscles of the uterus from contracting like they should after delivery. This can lead to excess bleeding.

Uterine rupture: If you’ve had a past cesarean delivery or uterine surgery, the uterus can tear during delivery. This complication could be life-threatening.

Problems with the baby that may arise include:

Obesity: Babies born at a heavier weight are more likely to be obese in childhood.

Abnormal blood sugar: Some babies are born with lower than normal blood sugar. Less often, blood sugar is high.

Babies born large are at risk for these complications in adulthood:

  • Diabetes
  • High blood pressure
  • Obesity

They’re also at risk of developing metabolic syndrome. This cluster of conditions includes high blood pressure, high blood sugar, excess fat around the waist, and abnormal cholesterol levels. As the child gets older, metabolic syndrome can increase their risk for conditions like diabetes and heart disease.

Diagnosis and test

Macrosomia should be suspected if major risk factors (such as maternal obesity or diabetes) are present. In addition to asking about your medical history, doctors can assess the baby’s size using the following methods:

Ultrasound: Ultrasound technology is the most accurate method used to estimate fetal size. Hadlock’s formula (which takes into account head circumference, abdominal circumference, and femur length) is thought to be the most accurate sonographic method for estimating fetal weight.

Fundal height measurement: The fundal height refers to the length from a woman’s pubic bone to the top of her uterus. A higher than normal fundal height could indicate macrosomia.

Palpation of the maternal abdomen: Physicians can estimate fetal weight by palpating the mother’s abdomen (a common method is called the “Leopold maneuver”).

Checking amniotic fluid level: An excess of amniotic fluid (polyhydramnios) can be indicative of macrosomia because larger babies produce more urine (late in pregnancy, the amniotic fluid is made up primarily of fetal urine).

Nonstress test: This records the baby’s heart rate when they move. Abnormal results of a nonstress test should be taken as a warning sign that something may be wrong with the pregnancy or the baby.

A biophysical profile (BPP): This uses the nonstress test in conjunction with ultrasound to check the baby’s movements, heart rate, and level of amniotic fluid.

If macrosomia is suspected, physicians should recommend frequent prenatal testing in order to assess fetal well being and determine whether medical intervention is necessary.

Treatment and medications

When it’s time for your baby to be born, a vaginal delivery won’t necessarily be out of the question. Your health care provider will discuss options as well as risks and benefits. He or she will monitor your labor closely for possible signs of a complicated vaginal delivery.

Inducing labor stimulating uterine contractions before labor begins on its own isn’t generally recommended. Research suggests that labor induction doesn’t reduce the risk of complications related to fetal macrosomia and might increase the need for a C-section.

Your health care provider might recommend a C-section if:

  • You have diabetes If you had diabetes before pregnancy or you develop gestational diabetes and your health care provider estimates that your baby weighs 9 pounds, 15 ounces (4,500 grams) or more, a C-section might be the safest way to deliver your baby.
  • Your baby weighs 11 pounds or more and you don’t have a history of maternal diabetes. If you don’t have pre-gestational or gestational diabetes and your health care provider estimates that your baby weighs 11 pounds (5,000 grams) or more, a C-section might be recommended.
  • You delivered a baby whose shoulder got stuck behind your pelvic bone (shoulder dystocia). If you’ve delivered one baby with shoulder dystocia, you’re at increased risk of the problem occurring again. A C-section might be recommended to avoid the risks associated with shoulder dystocia, such as a fractured collarbone.

If your health care provider recommends an elective C-section, be sure to discuss the risks and benefits.

After your baby is born, he or she will likely be examined for signs of birth injuries, abnormally low blood sugar (hypoglycemia) and a blood disorder that affects the red blood cell count (polycythemia). He or she might need special care in the hospital’s neonatal intensive care unit.

Keep in mind that your baby might be at risk of childhood obesity and insulin resistance and should be monitored for these conditions during future checkups.

Also, if you haven’t previously been diagnosed with diabetes and your health care provider is concerned about the possibility of diabetes, you may be tested for the condition. During future pregnancies, you’ll be closely monitored for signs and symptoms of gestational diabetes – a type of diabetes that develops during pregnancy.

Prevention of Fetal Macrosomia

Fetal macrosomia is unpredictable. The diagnosis is made only after the baby has been weighed after delivery. Babies can be born larger than average with or without any of the known risk factors.

Promoting good health and a healthy pregnancy can improve the odds:

  • See a doctor for regular prenatal care. Frequent visits allow you and your doctor to closely follow your baby’s progress, and also give you a chance to ask questions. Your doctor will make up a schedule for you.
  • Watch your weight. Your weight before pregnancy matters, as does how much weight you put on while you are pregnant.
  • If you have diabetes, take appropriate steps to manage it. Diabetes before the pregnancy and diabetes that occurs during the pregnancy (gestational diabetes) are risk factors for fetal macrosomia. Gestational diabetes usually goes away after the baby is born, but women who have had it have a greater risk for diabetes later in life.

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