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Macrosomia and Large for Gestational Age Babies

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You are asked to come to the labour ward and examine a baby girl, Mantre, born at 41 weeks and two days.

Her mom has poorly controlled gestational diabetes.

Mantre weighs 4280 grams.

You wonder: is this weight too much for the gestational age? Is this because of maternal diabetes? And what should I do next?

What is large for gestational age?

It is impossible to practice neonatology without coming across babies that are large for gestational age (LGA). Being LGA and/or having, macrosomia is associated with adverse health outcomes and is a reason for a closer look.

There is some confusion about the different definitions, as macrosomia and being large for gestational age are often, erroneously, mixed up.

Large for gestational age refers to a group of neonates who weigh more than a certain percentile of the normal weight distribution in a population for a specific gestational age. This percentile may differ in scientific studies and by hospital. It could be above the 90th percentile, the 95th, or the 97.7th.

Generally, a distinction is made based on sex, yielding different curves for boys and girls. Still, more distinctions can be made (e.g. the first-born child versus multiparity and by ethnicity). There are two main types of curves:

There is some evidence that prescriptive weight curves, by omitting greater groups of women, are better at predicting future morbidity than descriptive curves, but the jury is still out. However, classifying babies as LGA that may not have a higher underlying risk of morbidity may result in overtreatment. Using the correct curve avoids unjustly classifying LGA babies as having appropriate weight and vice-versa (the same goes for babies that are small for gestational age).

What is macrosomia?

Macrosomia is an absolute number – typically, a baby weighing more than 4000 grams at birth is considered macrosomic. Macrosomia is independent of gestational age. Babies can be LGA without having macrosomia, e.g. weighing 3800 grams at 36 weeks gestation.

Macrosomia is sometimes divided into grades:

  • Grade 1 (weight between 4-4.5 kg),
  • Grade 2 (4.5-5.0 kg), and
  • Grade 3 (>5 kg).

This may help the obstetricians make management decisions, but rarely the paediatricians.

Why are some babies bigger than others?

LGA babies are large because of high maternal glucose levels in utero. These high glucose levels induce high insulin levels in the fetus, leading to increased glucose metabolism in tissues and fat deposition. Being LGA or having macrosomia can be caused by the following:

What are the risks of a larger baby?

Risks to the mother include obstructed labour, caesarean section, postpartum haemorrhage, and peripartum injury (e.g. anal sphincter injury).

The consequences for the baby are:

In utero

  • A higher risk of foetal bradycardia/hypoxia and intra-uterine death

Around delivery

  • Lower Apgar scores, meconium aspiration, and respiratory distress.
  • Problems due to obstructed delivery include shoulder dystocia, associated fractures of the collar bone and femur, and brachial plexus injury.

After delivery

  • Hypoglycaemia, and if not treated properly, its long-term neurological consequences.
  • Polycythaemia.
  • Term LGA newborns are at a higher risk of mortality than children with the appropriate weight, but this is only the case in grade II-III macrosomia or above.
  • There are some indications that pre-term babies that are LGA are better off than pre-term babies with appropriate weight.

In the long term, LGA babies are at higher risk of metabolic syndrome and obesity.

What next for a large for gestational age baby?

Adequate diabetes and weight control during pregnancy are important but hard to achieve.

After delivery, babies with LGA should be examined to see if there are any dysmorphic features.

Glucose levels should be monitored, and if hypoglycaemia arises, treated by increasing oral feeds, giving oral dextrose gel, or intravenous glucose, depending on the circumstances. If there are signs of polycythaemia, check a haematocrit.

References

Beta J et al. Maternal and neonatal complications of fetal macrosomia: systematic review and meta-analysis. Ultrasound Obstet Gynecol 2019;54:308-18.

Choi SKY et al. Performance of six birth-weight and estimated-fetal-weight standards for predicting adverse perinatal outcome: a 10-year nationwide population-based study. Ultrasound Obstet Gynecol 2021;58:264-77.

Cochrane Neonatal Group. Oral dextrose gel to prevent hypoglycaemia in at‐risk neonates. Cochrane Database Syst Rev 2021;5:CD012152

Francis J et al. Perinatal mortality by birthweight centile. ANZJOG 2014;54:354-9.

Hoftiezer L et al. Defining small-for-gestational-age: prescriptive versus descriptive birthweight standards. Eur J Pediatr 2016;175:1047-57.

Hoftiezer L et al. Prescriptive birthweight charts can improve the prediction of adverse outcomes in very preterm infants who are small for gestational age. Acta Pediatrica 2018;107:981-9.

Homko CJ et al. The interrelationship between ethnicity and gestational diabetes in fetal macrosomia. Diabetes Care 1995;18:1442-5.

Nahavandi S et al. Exploration of the shared pathophysiological mechanisms of gestational diabetes and large for gestational age offspring. World J Diabetes 2019;10:333-40.

Vora N & Bianchi DW. Genetic considerations in the prenatal diagnosis of overgrowth syndromes. Prenat Diagn 2009;29:923-29.

Xu H et al. Optimal birth weight percentile cut-offs in defining small- or large-for-gestational-age. Acta Paediatr 2010;99:550-5.

Author

  • Marijn is a resident in paediatrics at the Sophia Children's Hospital in Rotterdam, the Netherlands. He is interested in infectious diseases, neonatology, and acute medicine. In his free time he likes to play tennis, read books, and worship his two cats.

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