Fetal macrosomia describes a newborn who is considerably larger than average for their gestational age. This condition, indicating excessive growth in the womb, can present specific considerations for both the birthing parent and the infant around the time of birth.
Understanding Macrosomia
Macrosomia is defined as a birth weight exceeding 8 pounds, 13 ounces (4,000 grams), regardless of the baby’s gestational age. Risks increase when the birth weight surpasses 9 pounds, 15 ounces (4,500 grams). While the exact weight is known only after birth, healthcare providers estimate fetal weight during pregnancy.
Estimates involve measuring fundal height, the distance from the top of the uterus to the pubic bone. A larger than expected fundal height can suggest a larger baby. Ultrasound scans also estimate fetal weight using biometric measurements like head circumference, abdominal circumference, and femur length. These prenatal estimation methods can be inaccurate, and macrosomia is confirmed only after delivery.
Factors Increasing Macrosomia Risk
Several factors increase the likelihood of macrosomia. Maternal diabetes, whether pre-existing or gestational, is a major contributor. If a birthing parent’s diabetes is not well-managed, the baby may gain excess weight, particularly in the shoulders and body fat.
Maternal obesity and substantial weight gain during pregnancy elevate the risk. A higher pre-pregnancy body mass index (BMI) and excessive gestational weight gain are linked to increased fetal growth. Genetic factors play a role, as larger parents are more likely to have larger babies, and male infants typically weigh more than female infants.
Post-term pregnancy, where a pregnancy extends beyond the due date, increases the risk because babies continue to gain weight, approximately 150-200 grams weekly, near term. A history of macrosomia in a previous pregnancy raises the chance of recurrence. Birthing parents older than 35 years are also more likely to have a baby diagnosed with macrosomia.
Potential Complications for Mother and Baby
Macrosomia can lead to challenges for both the birthing parent and the newborn. For the baby, birth injuries are a concern, including shoulder dystocia (where the baby’s shoulder gets stuck during delivery). This can lead to nerve damage, such as brachial plexus injury, or a fractured collarbone.
After birth, macrosomic infants may experience hypoglycemia (low blood sugar), requiring close monitoring and intervention. There is an increased long-term risk for these babies to develop childhood obesity and metabolic syndrome. Breathing problems can also occur shortly after delivery.
For the birthing parent, macrosomia can result in difficult labor and delivery due to the baby’s size. This increases the likelihood of needing a cesarean section. Other potential complications include postpartum hemorrhage (excessive bleeding after birth) and perineal tears or injuries during a vaginal delivery.
Managing and Preventing Macrosomia
Managing macrosomia involves strategies before and during pregnancy to reduce risks. For those with pre-existing diabetes or gestational diabetes, maintaining strict blood sugar control through diet, regular exercise, and medication when necessary is recommended. Achieving and maintaining a healthy weight before and throughout pregnancy can help mitigate the risk of excessive fetal growth. Consistent prenatal care allows healthcare providers to monitor the birthing parent’s health and the baby’s growth.
During pregnancy, if macrosomia is suspected, fetal growth is closely monitored through regular assessments. As labor approaches, healthcare providers discuss delivery options, considering factors such as estimated fetal weight and the birthing parent’s medical history. While a vaginal delivery is often possible, a cesarean section may be recommended for suspected birth weights above 9 pounds, 15 ounces (4,500 grams), especially in birthing parents with diabetes, to reduce the risk of complications.