Macrosomia

What is Macrosomia?

Macrosomia is a term, originating from the Greek words “macro” (big) and “somia” (body), used in pregnancy care to describe a baby who is significantly larger than average. The term itself was first used by an English doctor, Robley Dunglison, in the late 18th and early 19th centuries. However, its use in today’s medical field, according to the American College of Obstetrics and Gynecology (ACOG), is slightly different.

Nowadays, medical professionals use two main terms to describe excessive growth of a baby before it’s born: “large for gestational age” (LGA) and “macrosomia”. When a baby is described as LGA, it means the baby’s weight is equal to or exceeds the highest 10% of babies for the same stage of pregnancy. On the other hand, “macrosomia” refers to any baby that reaches a certain weight, typically either 4,000 g or 4,500 g, no matter how long they’ve been in the womb. However, it’s worth noting that medical experts still debate the exact definition of macrosomia.

It’s important to understand that having a significantly larger-than-average baby can pose serious risks to both the mother and baby, so careful monitoring and appropriate care are essential.

What Causes Macrosomia?

Fetal macrosomia, or having a baby that’s larger than usual, can be triggered by two main categories of causes: conditions related to the mother and conditions related to the baby.

Mother-related Causes

1. Diabetes during pregnancy: This could either be a type of diabetes that only affects pregnant women (gestational diabetes), a type of diabetes where insulin use is required, or diabetes caused by medications or chemicals. It is believed that if the mother has high blood sugar levels, this could lead to the baby also having high blood sugar levels and producing a lot of insulin, a hormone that controls blood sugar levels. This could then cause the baby to use too much glucose (a type of sugar), leading to abnormal growth.

2. Obesity: Obesity has become a global problem and it’s a significant risk factor for developing diabetes. Specifically, if the mother is obese, this could increase the chances of having an unusually large baby four to twelve-fold.

3. Having several children: While this doesn’t pose as high a risk as other factors, having more children than average (multiparity) could contribute to obesity and diabetes in women. It has been observed that women who have had more than three children are more likely to have unusually large babies. Each pregnancy could also lead to a weight gain of 100 to 150 grams, which may increase the risk of having a big baby in the long run.

4. Previous unusually large babies: Women who have previously given birth to big babies are five to ten times more likely to have another big baby.

5. Extended pregnancy: Pregnancy lasting more than 42 weeks could increase the chances of having a large baby due to continuous nutrient supply and oxygen-rich blood to the growing baby.

Baby-related Causes

1. Gender of the baby: Unusually large babies are more commonly found among male babies. This might be partly because male babies tend to be about 150 grams heavier than female babies.

2. Genetic and congenital disorders: Certain inherited and birth disorders have been linked with unusually large babies. These include:

* Beckwith-Weiderman syndrome
* Sotos syndrome
* Fragile X syndrome
* Weaver syndrome

Risk Factors and Frequency for Macrosomia

According to a report on vital statistics from the U.S. in 2015, seven percent of infants weighed more than 4000 grams at birth, and one percent weighed over 4500 grams. Various factors can influence a baby’s size at birth. These include the age and race of the parent, their genetic makeup, and their ethnic background. Among these groups, Hispanic women have been seen to have a higher risk of giving birth to a larger than average baby.

Signs and Symptoms of Macrosomia

Pregnancy is a natural condition that requires careful monitoring from the beginning to the end. It’s especially important for women with high-risk pregnancies to have regular check-ups.

During the first visit and the following ones, the doctor will take a detailed history. This includes the following information:

• The first day of your last menstrual period
• Your pregnancy’s current stage
• How many pregnancies you’ve had before
• Your weight before the pregnancy
• Your immunization history
• Any existing or previous medical conditions, such as diabetes, obesity, or RH incompatibility
• Details about your past pregnancies, including any complications, the baby’s gender, and how the baby was delivered

Along with a detailed history, your physician will perform a thorough physical examination. It involves monitoring your weight at each visit and comparing it with standard guidelines. For example:

• If your body mass index (BMI) is less than 18 kg/m^2, a weight gain of 28-40 lbs (12-18 kg) is suggested.
• If your BMI is between 18.5 to 24.9 kg/m^2, you should gain 25-35 lbs (11.5-16 kg).
• If your BMI is between 25.0 to 29.9 kg/m^2, a weight gain of 15-25 lbs (7-11.5 kg) is recommended.
• If your BMI is more than 30 kg/m^2, you should gain 11-20 lbs (5-9 kg).

If your weight gain deviates from these recommendations, your obstetric provider will conduct additional checks, like measuring your belly size and performing the Leopold’s maneuver. Diagnosis of a larger than normal baby, known as macrosomia, isn’t accurately done by any single technique. The best method is to weigh the newborn after birth. However, if there are multiple indicators of a large baby, your doctor might suspect macrosomia.

Testing for Macrosomia

If there’s a concern that a pregnant woman has high blood sugar (hyperglycemia), which can result in a larger than normal baby (fetal macrosomia), certain screening tests will be performed.

Between 24 to 28 weeks of pregnancy, a glucose challenge test might be given. This involves consuming a sugary drink and then having blood drawn an hour later. If the blood sugar level is over 140 mg/dL, that’s considered abnormal.

If the first test’s results are abnormal, a more detailed glucose test is needed. Gestational diabetes, a condition where a woman develops diabetes during her pregnancy, is confirmed when at least two of the following readings are abnormal:

• Fasting glucose over 95 mg/dL
• Glucose over 180 mg/dL one hour after eating
• Glucose over 155 mg/dL two hours after eating
• Glucose over 140 mg/dL three hours after eating

Additional tests during pregnancy may include monitoring blood pressure to check for a condition called pre-eclampsia, a full blood count, urine tests, monitoring kidney function, checking cholesterol levels and liver function tests. Regular ultrasound scans of the baby may also be performed.

As for the baby, if macrosomia (meaning the baby is larger than usual) is a concern, the baby will need to be closely monitored. Once the baby is born, blood levels for various elements are checked immediately. These include:

• Glucose levels: after separating from the glucose-rich environment inside the mother’s body, babies born to diabetic mothers can have low glucose levels (hypoglycemia).
• Calcium levels: low levels of calcium (hypocalcemia) and spasms (tetany) can occur.
• Magnesium levels: low levels of magnesium (hypomagnesemia) can also occur.
• Bilirubin levels: high levels of bilirubin may occur due to an inefficient process of breaking down and removing bilirubin from the body, as well as increased red blood cell breakup (hemolysis) if there are too many red blood cells (polycythemia).
• Complete blood count: this confirms if there are too many red blood cells, a condition known as polycythemia.

The doctors will also watch the baby’s breathing right after birth. This is because larger babies, especially if caused by pregnancy-induced diabetes, are more likely to have breathing problems, such as inhaling meconium (a baby’s first stool) due to stress during birth, or having fast breathing (transient tachypnea).

Treatment Options for Macrosomia

Managing a condition known as macrosomia, which is when a baby is significantly larger than average for its gestational age, can be complex and requires a multifaceted approach. There’s no clear-cut way to handle this condition, but there are a few things doctors usually consider.

Until recently, doctors often used a method called Induction of Labor (IOL) to manage macrosomia. IOL is a process where labor is triggered artificially. However, this practice is now discouraged due to a lack of strong evidence of its effectiveness for macrosomia.

If the mother has diabetes (either pre-existing or gestational diabetes, which develops during pregnancy), the risk of macrosomia can be reduced by managing the diabetes more effectively using specific medications and other interventions. This is because macrosomia often happens when diabetes is not well-controlled.

But the situation is a bit different if the baby is macrosomic and the mother doesn’t have diabetes. In these cases, the American College of Obstetrics and Gynecology (ACOG) advises considering an elective caesarian delivery if the estimated fetal weight is above 5000 g (which is about 11 pounds) and if there’s no underlying diabetes. If the mother has diabetes, the ACOG advises considering a caesarian delivery if the estimated fetal weight is above 4500 g (about 10 pounds).

Another option is assisted vaginal delivery. This procedure could involve using instruments such as forceps or a vacuum to help deliver the baby. But it’s important to proceed with caution with this option if the baby is macrosomic.

What about preventing macrosomia in the first place? Two key factors are maternal diabetes and excessive weight gain during pregnancy. Keeping diabetes under control, with a tailored diet plan and appropriate insulin therapy, could substantially lower the chance of having a macrosomic baby. On top of that, a well-planned, gradual exercise program can help prevent excessive weight gain during pregnancy. And if the mother has no other risk factors, these measures could significantly reduce the long-term risk of macrosomia.

What else can Macrosomia be?

The following conditions can make it difficult to accurately assess a pregnancy:

• Polyhydramnios (excess amniotic fluid)
• Inaccurate estimation of gestational age (how far along the pregnancy is)
• Multiple pregnancies (twins, triplets, etc.)
• Uterine anatomic lesions such as fibroids or adenomyosis
• Pelvic masses such as ovarian masses
• Morbid obesity
• Post-date pregnancies (going beyond the due date)

What to expect with Macrosomia

If a mother gives birth to a very large baby, which we call ‘macrosomic’, it’s important that she is thoroughly checked for diabetes that she may not know she has. If those tests show she does not have diabetes, it’s important that her health is closely watched in any future pregnancies.

The aim of planning a cesarean section birth for a suspected larger than normal baby is to lessen the chances of health problems for both mother and baby. Even though health problems for mother and baby increase with birth weights over 8.8 lbs (4000 g), most births of larger than normal babies happen without complications.

Possible Complications When Diagnosed with Macrosomia

When a baby is significantly larger than average, or “macrosomic,” it can cause complications for both the mother and the baby. These complications, along with their causes, can be broken down into two main categories:

Mother Related Complications:

• Postpartum hemorrhage: This refers to excessive blood loss (more than 500 mL) after a vaginal delivery, or a loss of 1000 mL or more with a cesarean section. This can happen if the uterus doesn’t contract properly after birth, a condition known as uterine atony. This can be worsened by having a very large baby.
• Perineal trauma: Trauma to the area between the vagina and anus can happen because of longer labor or interventions needed to deliver a larger baby.
• Extended second phase of labor: Labor can last longer with a macrosomic baby.

Baby Related Complications:

• Shoulder dystocia: This is when the baby’s shoulder gets stuck during vaginal delivery. It can also cause injury to the baby’s collar bone or nerves in the upper arm. The risk of this happening increases with the baby’s weight.
• Fetal distress: Large babies are at a greater risk of fetal distress, or indications of trouble during labor.
• Congenital anomalies: Various birth defects can occur, particularly in babies born to diabetic mothers. These can involve the heart, spine, and other parts of the body.
• Metabolic and electrolyte imbalance: Big babies may face issues like low blood calcium or magnesium, high insulin levels, low glucose levels.
• Polycythemia: This is a condition characterized by an unusually high level of red blood cells, which could occur in large babies.
• Hyperbilirubinemia: This refers to higher levels of a substance called bilirubin in the baby’s blood. This might lead to jaundice in newborns.

Preventing Macrosomia

If a woman gives birth to a very large baby (a condition known as macrosomia), she should be aware that her chances of experiencing it again in a future pregnancy are two to four times higher. During pregnancy classes, it’s very important that all expectant mothers are educated about the risks of gaining too much weight during their pregnancy.

After giving birth, women who experienced gestational diabetes, a form of high blood sugar that affects pregnant women, should be checked for developing prediabetes or type 2 diabetes. Prediabetes is a condition where blood sugar levels are high, but not high enough yet to be classified as type 2 diabetes. It’s also important to note that women who develop gestational diabetes are three to seven times more likely to develop type 2 diabetes within… five to ten years after childbirth.