Foetal macrosomia is a condition in which the body weight of the neonate is between 4000g to 4500g, irrespective of the gestational age. This is very commonly related to the development diabetes in pregnancy. Hence, early screening for diabetes during pregnancy and preventing it can help to deal with macrosomia related complications in both the mother and the infant. Foetal macrosomia is difficult to accurately diagnose and this can only be done retrospectively after delivery of the neonate. Nevertheless, some predictors are still used to detect the presence of the same.
Relationship between Diabetes and Foetal Macrosomia
The foetus is entirely dependent on the mother for its glucose requirements. With transporters like GLUT1 and GLUT3, there is facilitated diffusion of glucose molecules from the maternal bloodstream to the foetus. Therefore, it is fair to say that maternal hyperglycemia ultimately leads to foetal hyperglycemia. As a result of this, the pancreatic beta cells of the foetus undergo hypertrophy. Hypertrophied beta cells, in turn secrete more insulin and insulin like growth factors (IGF), the principal hormones for foetal growth leading to foetal macrosomia.
Diabetes Mellitus in pregnant women can be classified into two categories.
- Overt diabetes mellitus: where a female previously diagnosed with diabtetes, conceives. The chances of the foetus developing cardiovascular and CNS malformations apart from macrosomia are higher in this case due to the production of free radical from the very first day of conception.
- The other case is where a female who previously did not have diabetes, develops the condition after conceiving, somewhere between 24-28 weeks of gestation causing gestational diabetes. Congenital malformations are do not occur this situation as by 24-28 weeks, foetal organogenesis is complete.
Screening for diabetes mellitus in the pregnant people is done by conducting a Glucose Challenge test at 24-28 weeks, where 50g glucose is administered to the woman orally and blood sugar levels are checked after an interval of 1hour. A blood glucose level of ≥180mg/dL confirms gestational diabetes. The advantage of this Glucose Challenge test is that overnight fasting is not required unlike the other blood glucose tests. However, for overt diabetes mellitus, it is vital to measure the glycosylated haemoglobin (HbA1c) which predicts the degree of foetal anomalies. If it is between 6.5-9.5%, there is a 5% chance of developing foetal malformations. The woman is placed on strict glycaemic control and advised to maintain HbA1c below 6.5 along with folic acid supplementation to prevent congenital malformations.
Managing maternal diabetes mellitus becomes is vital to prevent morbidity in the mother and foetus. Oral hypoglycemic drugs are contraindicated during pregnancy as they cross the placental barrier and cause hypoglycemia in the foetus. However, Oral Metformin and Glyburide have been prescribed to women with gestational diabetes but not with overt diabetes. Studies have found Metformin to be non-teratogenic and the most common side effect it causes is gastric disturbance. Intravenous Insulin remains the main stay for treatment of maternal hyperglycemia. However it is necessary to reduce IV insulin dosage during delivery to prevent neonatal hypoglycemia.
Other risk factors that predisposes foetal macrosomia are:
- Excess weight gain or BMI ≥ 25
- Previous history of delivering macrosomic foetus
- Maternal age≥ 35
- Post dated pregnancy
- Abdominal circumference ≥ 35cm on Ultrasonography predicts macrosomia in foetus
Complications of Foetal Macrosomia
- Shoulder dystocia (aka Turtle Sign) is defined as the delay in the delivery of the shoulders by ≥1 minute after delivery of the head in a vaginal delivery. This complication occurs due to excess fat deposition around the shoulders and they are unable to pass through the relatively narrow birth canal. Complications of shoulder dystocia include injury to brachial plexus and fracture of clavicle in order to deliver the shoulder.
- Post Partum Haemorrhage in the mother due to prolonged labour and other invasive procedures conducted to help deliver the foetus. An episiotomy is always required in shoulder dystocia which causes considerable blood loss.
- Lateral femoral cutaneous nerve injury while performing McRoberts manoeuvre which includes flexing the legs against the abdomen.
- Neonatal hypoglycemia is seen soon after delivery in case of diabetes mellitus because the high circulating insulin from the foetal pancreas is still present, but the maternal glucose is no longer present. Therefore, blood sugar level of the neonate falls rapidly and it can be fatal.
Management of foetus with macrosomia
Foetal surveillance is recommended to begin at 32-34 weeks of gestation. Method of surveillance includes daily foetal kick counts and weekly biophysical score. Admission is suggested in case of overt diabetes at 34 weeks. Vaginal deliver is not recommended if weight of the foetus is ≥ 4.5kg. Perform caesarean section at ≥ 39weeks ± 6 days.