Fetal Macrosomia – Symptoms and Causes
About Large Babies
When a baby weighs more than 8 pounds, 13 ounces at birth, doctors call this “large for gestational age” or “fetal macrosomia.” About 9% of babies worldwide are born this large.
The risks become much higher when babies weigh more than 9 pounds, 15 ounces. These large babies may face delivery complications and health issues after birth.
For mothers carrying large babies, healthcare providers may recommend:
- Extra monitoring during pregnancy
- Special delivery planning to reduce injury risks
- Blood sugar testing if diabetes is suspected
- Nutritional counseling to manage weight gain
Warning Signs
Measuring Uterus Size
The distance from your pubic bone to the top of your uterus is called the fundal height. Healthcare providers measure this in centimeters during prenatal visits.
After 24 weeks of pregnancy, this measurement often matches how many weeks pregnant you are.
A fundal height larger than expected for your stage of pregnancy might suggest your baby is growing bigger than average. This can be one of the first clues that your healthcare provider notices when checking for a larger baby.
Excess Amniotic Fluid
Having too much amniotic fluid around your baby is called polyhydramnios. This condition can be a sign that your baby is larger than normal. The amount of amniotic fluid reflects how much urine your baby produces.
Larger babies typically produce more urine, which increases the fluid volume.
Polyhydramnios can range from mild to severe:
- Mild cases may resolve without treatment
- Severe cases might require medical intervention
Some conditions that cause babies to grow larger may also increase how much they urinate, leading to this excess fluid. Your healthcare provider can detect this during ultrasounds and physical exams.
Causes
Different factors can make a baby grow larger than normal before birth. These include:
- Genetic factors passed down from parents
- Maternal health issues like obesity or diabetes
In some rare cases, a baby may have a medical problem that causes faster growth. Sometimes doctors can’t find a clear reason why a baby is bigger than average.
Risk Factors
Several factors can increase the chance of having a large baby (fetal macrosomia). Some of these factors can be controlled, while others cannot.
Medical Conditions
- Diabetes: Women who had diabetes before pregnancy or develop it during pregnancy (gestational diabetes) are more likely to have larger babies. Poor blood sugar control can lead to babies with larger shoulders and more body fat.
- Obesity: Women who are obese have a higher risk of delivering larger babies.
Pregnancy History
- Previous Large Babies: If you’ve had a large baby before, you’re more likely to have another one.
- Your Own Birth Weight: If you weighed more than 8 pounds, 13 ounces at birth, you have a higher chance of having a large baby.
- Number of Pregnancies: The risk increases with each pregnancy, up to the fifth. Each baby may weigh about 4 ounces more than the previous one.
Other Factors
- Weight Gain: Gaining too much weight during pregnancy raises the risk.
- Baby’s Sex: Boys typically weigh more than girls. Most babies weighing over 9 pounds, 15 ounces, are male.
- Overdue Pregnancy: Babies born more than two weeks past the due date have an increased risk of being larger.
- Mother’s Age: Women over 35 are more likely to have larger babies.
When diabetes, obesity, or excessive weight gain aren’t present but a large baby is suspected, the baby might have a rare medical condition affecting growth.
In these cases, healthcare providers might recommend special tests or a meeting with a genetic counselor.
Risk Factor Summary Table
| Type of Risk Factor | Examples |
|---|---|
| Medical | Diabetes, obesity |
| History | Previous large babies, mother’s birth weight |
| Pregnancy-related | Excessive weight gain, multiple pregnancies |
| Unavoidable | Baby’s sex, mother’s age, overdue pregnancy |
Understanding these risk factors can help healthcare providers monitor pregnancies more closely when needed.
Health Risks
Risks for the Mother
When a baby is unusually large before birth, mothers face several possible complications.
During Labor and Delivery:
- Difficult Delivery: The baby may become stuck in the birth canal (shoulder dystocia).
- Need for Assisted Delivery: Doctors might use forceps or vacuum devices.
- Emergency C-section: Often required when vaginal delivery becomes unsafe.
- Tears and Injuries: The birth canal, vaginal tissues, and perineal muscles can tear.
After Childbirth:
- Excessive Bleeding: The uterus may not contract properly after delivery.
- Uterine Rupture Risk: Especially concerning for women with previous C-sections or uterine surgeries.
Risks for the Baby
Larger-than-normal babies may experience both immediate and long-term health challenges.
Short-Term Concerns:
- Low blood sugar levels immediately after birth
- Higher risk of birth injuries
- Breathing difficulties
Long-Term Health Risks:
- Greater chance of childhood obesity
- Higher risk of developing metabolic syndrome in childhood, which includes:
- High blood pressure
- Abnormal blood sugar levels
- Excess body fat around the waist
- Unhealthy cholesterol levels
These conditions can increase the child’s future risk of serious health problems. Scientists are still studying whether these babies face higher risks of adult diabetes, heart disease, and obesity.
Prevention
Preventing a larger-than-average baby starts before pregnancy. Taking certain steps can help reduce risks.
Before Pregnancy
- Schedule a pre-pregnancy appointment with your doctor.
- If you have obesity, consider meeting with a nutrition specialist to reach a healthier weight.
During Pregnancy
- Track your weight gain carefully.
- For those with normal pre-pregnancy weight, aim for 25-35 pounds (11-16 kg).
- Women with higher starting weights typically need less pregnancy weight gain.
Managing Medical Conditions
- Control diabetes if you have it before pregnancy.
- Monitor and manage gestational diabetes closely.
- You should do regular blood sugar testing.
- Follow your healthcare provider’s treatment plan.
Physical Activity
- Exercise regularly as recommended by your doctor.
- Research shows regular physical activity helps prevent excessive birth weight.
- You should also follow a low-glycemic diet to help maintain healthy blood sugar levels.
Work with Your Healthcare Team
- Attend all prenatal appointments.
- Discuss any concerns about baby’s growth.
- Follow nutrition recommendations from your healthcare provider.
