A large for gestational age (LGA) infant refers to a fetus whose birth weight is at or above the 90th percentile for gestational age. Macrosomia refers specifically to a neonate with a birth weight of 4,000 g or more.
Risk Factors
Key risk factors for macrosomia include the following:
- Maternal obesity
- Hyperglycemia during pregnancy, particularly type 2 diabetes
- Post-term pregnancy
- Multiparity
- Tall stature of both parents
- Advanced maternal age
- A history of delivering a macrosomic baby
- Ethnic or racial factors
Maternal and Fetal Impacts
Maternal Impact
Macrosomia increases the risk of cephalopelvic disproportion and thus raises rates of cesarean delivery. The primary risk during vaginal delivery is shoulder dystocia, which occurs at rates proportional to fetal weight. Improper management of shoulder dystocia may lead to severe vaginal trauma, perineal tears, or even uterine rupture. Overdistension of the uterus can cause uterine atony, prolonged labor, and postpartum hemorrhage. Prolonged compression of the birth canal by the presenting part may also result in urinary or fecal fistulas.
Fetal Impact
The increased fetal weight often necessitates operative delivery, creating risks of birth trauma such as intracranial hemorrhage, clavicle fractures, or brachial plexus injuries. In severe cases, neonatal mortality may occur.
Long-Term Impact
Macrosomic infants face an elevated risk of developing obesity, impaired glucose tolerance, and metabolic syndrome during childhood and adulthood.
Diagnosis
Currently, no definitive method exists to accurately predict fetal size before birth. Fetal weight is estimated through maternal history, clinical findings, and auxiliary examinations, but macrosomia is confirmed only upon delivery.
History and Clinical Manifestations
Pregnant individuals with macrosomic fetuses often present with one or more of the above-listed risk factors. Excessive gestational weight gain, breathing difficulties, a sensation of abdominal heaviness, and bilateral flank pain commonly emerge in late pregnancy.
Abdominal Examination
A markedly distended abdomen, fundal height exceeding 35 cm, and palpation of a large fetus are common findings. The presenting part may be high and mobile. With a cephalic presentation, the fetal head typically engages poorly, frequently showing a positive "crossed pelvimetry sign." On auscultation, fetal heart tones are audible but tend to be located higher than usual.
Ultrasound Examination
Using parameters such as biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL), ultrasound estimates of fetal weight can be used to monitor intrauterine growth. However, predicting macrosomia through ultrasound remains challenging. An abdominal circumference exceeding the 90th percentile for gestational age indicates an increased risk of macrosomia.
Management
During Pregnancy
Pregnant individuals with risk factors for macrosomia benefit from enhanced antenatal management, including nutritional and exercise guidance, blood glucose monitoring, and screening for gestational diabetes. For those diagnosed with diabetes, blood sugar levels should be tightly controlled. For LGA fetuses with suspected genetic anomalies, invasive prenatal diagnostic methods may be considered when necessary. After reaching full-term gestation, factors such as fetal maturity, placental function, gestational age, and glycemic control are considered collectively to determine the appropriate timing of delivery.
During Labor and Delivery
Time to Delivery
Macrosomia is not an absolute indication for cesarean delivery. Suspected cases may warrant delivery at 39–40 weeks of gestation. If contraindications to vaginal delivery are absent, labor induction may be pursued.
Mode of Delivery
For fetuses with an estimated weight ≥4,000 g and concomitant diabetes, cesarean delivery is advisable.
For fetuses with an estimated weight ≥4,000 g without diabetes, a trial of vaginal delivery is an option, with relaxed thresholds for converting to cesarean delivery if complications arise. During labor, assessments should include thorough evaluations of fetal status; operative delivery methods, such as forceps or vacuum, may be utilized if necessary. Preparations to manage potential shoulder dystocia should be in place. Postpartum examinations of the cervix and vaginal canal are required to identify any soft tissue injuries, with measures taken to prevent postpartum hemorrhage.
Neonatal Care
Newborns should be monitored for hypoglycemia, with glucose checks performed 30 minutes after delivery. Glucose water feedings should begin 1–2 hours after birth to mitigate hypoglycemia, and breastfeeding should be initiated early. Mild cases of neonatal hypoglycemia can be managed with oral glucose, whereas severe cases may require intravenous glucose administration. Neonates are at an increased risk for hypocalcemia and may require calcium supplementation; this is typically delivered via intravenous administration of 1 ml/kg of 10% calcium gluconate mixed with glucose solution.