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Fetal Macrosomia - Causes, Complications, Diagnosis, and Treatment

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Fetal macrosomia is used to describe a newborn whose birth weight is larger than the average.

Medically reviewed by

Dr. Richa Agarwal

Published At August 19, 2022
Reviewed AtDecember 21, 2023

Introduction:

Fetal macrosomia (a Greek word, where ‘macro’ means big and ‘somia’ means body) is an obstetric condition where the newborn’s birth weight is larger than the average. This condition is seen in 3 % to 15 % of all pregnancies. In fetal macrosomia, the baby weighs more than 4000 grams (8 pounds and 13 ounces), irrespective of the gestational age. It is a potentially life-threatening complication to both the mother and the baby during labor. The risk furthermore increases when it is greater than 4500 grams (nine pounds and 15 ounces). Fetal macrosomia complicates vaginal delivery and has a high chance of injury to the baby and the mother during labor. These babies encounter an increased risk of health problems after birth. This article briefly explains fetal macrosomia, its symptoms, causes, and the treatment plan.

What Are the Symptoms of Fetal Macrosomia?

  • Polyhydramnios (Excessive Amniotic Fluid): In this condition, excessive fluid accumulation occurs in the uterus during pregnancy. Excess amniotic fluid (that surrounds and protects the baby) means the baby’s urine output is higher and suggests that a fetus is larger than average.

  • Large Fundal Height: The distance from the pubic bone to the top of the uterus is called fundal height. It usually matches the number of weeks of pregnancy, mainly after 24 weeks of gestation or pregnancy. Fetal macrosomia could exist if the fundal height is more than expected.

What Are the Risk-Factors Associated With Fetal Macrosomia?

Maternal Causes and Risk Factors:

  • Maternal Obesity: Fetal macrosomia is more likely to develop if a person is obese.

  • Maternal Diabetes: Pre or post-gestational diabetes, if not controlled well, can cause fetal macrosomia. The babies born to these mothers have greater amounts of body fat and bigger shoulders than those women who do not have diabetes.

  • Previous Pregnancies: With each pregnancy, the risk of fetal macrosomia increases, and the average birth weight of the fetus increases by four ounces with each successive pregnancy.

  • History of Fetal Macrosomia: If one has already given birth to a larger baby is more at risk of having another larger baby. Also, if a person has gained weight during pregnancy (more than eight pounds and 13 pounds at birth), the risk of fetal macrosomia is higher.

  • Overdue Pregnancy: If the pregnancy is more than two weeks than the expected due date (more than nine months), the chances for the baby to develop fetal macrosomia are higher.

  • Maternal Age: The age of women more than 35 years old are at risk of having a baby with fetal macrosomia.

Fetal Causes and Risk Factors:

  • Generally, male infants weigh heavier than female infants. Most cases of macrosomia are in male infants.

  • Presence of underlying genetic and congenital disorders.

  • Beckwith-Wiedemann syndrome (a genetic disorder characterized by overgrowth).

  • Sotos syndrome (characterized by excessive physical growth).

  • Fragile x syndrome (characterized by developmental and learning disabilities).

How Delivery Gets Affected if the Baby Is Too Large?

Fetal macrosomia poses health risks to the mom and the baby both during and after pregnancy. The maternal risks are,

  • Labor Problems: Macrosomia may cause problems during vaginal labor. The baby gets wedged in the birth canal, leading to a serious complication called “shoulder dystocia.”

Apart from that, they sustain birth injuries and may require the use of forceps or vacuum devices during delivery. In these cases, C-section may be preferred.

  • Genital Tract Lacerations: These babies cause injuries to the birth canal, such as tearing of vaginal tissues and muscles between the vagina and the anus.

  • Postpartum Hemorrhage: Fetal macrosomia increases the risk of uterine atony. It is a condition when the uterus fails to contract, leading to bleeding after delivery.

  • Uterine Rupture: This is a rare but serious condition that occurs when the mother had any prior uterine surgery or cesarean where the uterus opens along the scar line.

Fetal complications are,

  • During delivery, the baby may encounter an injury, fractures, or nerve damage.

  • Lower blood sugar level than the average value.

  • Childhood obesity.

  • Metabolic syndrome.

How Fetal Macrosomia Be Diagnosed?

Fetal macrosomia is often difficult to diagnose during pregnancy. However, regular prenatal visits help the clinician with suspected fetal macrosomia.

  • Large Fundal Height: The fundal height is measured regularly during routine visits, and large values above the average are suggestive of fetal macrosomia.

  • Polyhydramnios: Polyhydramnios is the excess amount of amniotic fluid. This fluid surrounds and protects the baby during pregnancy. The amount of amniotic fluid is indicative of the baby's urine output, and if the baby is large, a large amount of urine is produced, and the fluid level goes up. This may be suggestive of macrosomia in a baby.

What Is the Differential Diagnosis of Fetal Macrosomia?

  • Polyhydramnios.

  • Presence of uterine masses such as uterine myoma and adenomyosis.

  • Multiple gestations.

  • Pelvic masses such as ovarian mass.

How Fetal Macrosomia Be Prevented?

Fetal macrosomia may not be prevented, but early detection may promote a healthy pregnancy. Regular exercising and eating a low glycemic diet reduce macrosomia. Some measures for a healthier pregnancy journey include;

  • Have a preconception appointment with the doctor.

  • Managing the weight.

  • Managing diabetes.

  • Staying physically active.

What Is the Treatment of Fetal Macrosomia?

Fetal macrosomia can be managed by medical management and following proper diet and exercise.

  1. Medical Management:

  • Early Induction of Labor: The fetus continues to gain about 0.6 pounds per week after the 37th week. So, stimulating the uterine contractions before the labor begins on its own (naturally) is early labor induction. However, this is generally not recommended and may lead to a cesarean.

  • Elective Cesarean Surgery: To avoid any birth complications for the mother and the baby, a vaginal delivery is not frequently recommended. In such a case, an elective cesarean in a suspected case of macrosomia is advised to prevent birth trauma, which can prevent shoulder dystocia, brachial plexus injury, etc., in the baby.

2. Diet And Exercise:

The most important factor for macrosomia is uncontrolled maternal diabetes and excessive weight gain. So dietary control and insulin therapy reduce the chances of macrosomia in the baby, along with tolerable exercise programs for preventing weight gain.

Conclusion

Though macrosomia remains a challenging obstetric condition, healthy lifestyle management can be helpful throughout the pregnancy. The effective management and coordination of the interprofessional persons along with the obstetricians is the key to success in the case of pregnant mothers with macrosomic babies.

Frequently Asked Questions

1.

Is Macrosomia a Congenital Disorder?

Certain genetic factors cause macrosomia if the mother is diabetic or obese during pregnancy. In diabetic mothers, the sugar passes through the placenta and gets deposited as fat, leading to a large baby. Sometimes the reason for the baby being larger than normal is unknown.

2.

Are Pregnancies With Macrosomia Regarded as High-Risk?

The risks associated with macrosomia pregnancies are considered high-risk if the birth weight is more than nine pounds. This is because it makes vaginal delivery complicated and can lead to injuries during birth. In addition, it can also cause health issues in the baby after birth.

3.

What Factors Contribute to the Risk of Macrosomia?

Maternal obesity, diabetes, excessive weight gain during pregnancy, male sex, and post-term pregnancy contribute to the risk of macrosomia. These factors pose more significant risks to the mother and the fetus during delivery.

4.

Is Macrosomia a Fatal Condition?

Several studies suggest macrosomia as a fatal condition. But the infant’s death is determined by birth weight and is most commonly encountered in neonates weighing more than 4500 grams. Studies suggest the end of a fetus also depends on the diabetic and obese status of the mother.

5.

Can Macrosomia Be Identified With Ultrasound?

Fetal macrosomia can be diagnosed only after birth. However, if the mother has the risk factors, the baby’s health and development can be monitored using ultrasound. Furthermore, there is a possibility of identifying a macrosomic baby by measuring the fundal height, which involves assessing the distance from the uppermost point of the uterus to the pubic bone.

6.

Is Macrosomia a Common Condition?

Fetal macrosomia is not a very common condition. However, about 9 % of babies are born worldwide with fetal macrosomia. It also increases the risk of cesarean delivery and causes traumatic injury to the birth canal and the fetus.

7.

Does Macrosomia Indicate a C-Section?

A C-section can be performed if the weight of the fetus is more than ten pounds in a diabetic woman or eleven pounds or more in other women. It can also be considered a prerequisite if the mother is obese and diabetic. Initially, labor induction is considered. Then, if it fails, a cesarean is considered.

8.

How Much Weight Is Considered Fetal Macrosomia?

A weight of 4000 to 5000 grams or nine to ten pounds is considered fetal macrosomia, which is much larger than average. The severity of complications during labor depends upon the weight of the infants. And so, induction or elective cesarean is considered.

9.

How Much Weight May a Baby Have in a Regular Delivery?

A baby born in a regular delivery weighs about 2.5 to 4.5 kilograms. If they exceed 4.5 kilograms, then the condition is called fetal macrosomia. If the baby weighs less than 2.5 kilograms, it is considered a low birth weight commonly noticed in premature babies.

10.

Do Big Newborns Continue to Be Big?

No one can predict how big an infant with macrosomia will grow. However, studies have estimated a correlation between birth weight and adult size. The length of the baby is also associated with its height and weight.

11.

Do I Need to Be Induced for a Large Baby?

A healthy woman with a large baby is recommended to be induced into labor at 41 or 42 weeks. However, studies also suggest that earlier labor induction is a safe option. If induction is not found to be successful, an elective cesarean is performed.

12.

Does a Large Pregnancy Bump Indicate a Large Baby?

The large baby bump need not always indicate a large and healthy baby. It can also be due to excessive amniotic fluid that cushions the growing fetus. And this can lead to severe complications during birth if the mother is obese or short.
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Dr. Richa Agarwal
Dr. Richa Agarwal

Obstetrics and Gynecology

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