Pregestational Diabetes and Fetal Risk
A 28-year-old woman with type 1 diabetes for 12 years, on insulin, has an HbA1c of 7.2% and no family history of inherited disease. She and her husband are unrelated. She asks how her diabetes will affect the pregnancy she is planning. Which of the following risks is the same for her as for the general population?
- A.Fetal macrosomia
- B.Polyhydramnios
- C.Fetal cystic fibrosisCorrect
- D.Preeclampsia
Explanation
Cystic fibrosis is an autosomal recessive disorder determined entirely by parental CFTR carrier status, so maternal diabetes does not alter its risk; with no family history and unrelated parents her risk equals the population background. Every other listed complication is genuinely increased by pregestational diabetes. Maternal hyperglycaemia crosses the placenta and drives fetal hyperinsulinaemia, which acts as a growth factor and causes macrosomia with the attendant risks of shoulder dystocia, birth injury and caesarean delivery. Fetal hyperglycaemia also produces an osmotic diuresis with increased fetal urine output, giving polyhydramnios. Diabetes causes endothelial and microvascular dysfunction and is a major independent risk factor for preeclampsia, which is why these women start low-dose aspirin from 12 weeks. Additional diabetes-related risks include congenital malformations proportional to periconceptional HbA1c, particularly cardiac defects, neural tube defects and caudal regression, plus stillbirth, neonatal hypoglycaemia, hypocalcaemia, polycythaemia and respiratory distress syndrome. Preconception care with tight glycaemic control (target HbA1c under 6.5%), high-dose folic acid, and review of retinopathy and nephropathy substantially reduces these risks. The teaching point is to separate metabolically mediated complications from purely genetic conditions.
Why each option
- A.
- Fetal macrosomia is markedly increased because maternal hyperglycaemia drives fetal hyperinsulinaemia and excess growth.
- B.
- Polyhydramnios is more common because fetal hyperglycaemia causes an osmotic diuresis and increased urine output.
- C.
- Correct. Cystic fibrosis risk depends only on parental CFTR carrier status and is unaffected by maternal diabetes.
- D.
- Preeclampsia is substantially more frequent in pregestational diabetes because of underlying endothelial and microvascular disease.
Reference: ACOG Practice Bulletin 201, Pregestational Diabetes Mellitus (reaffirmed 2023); Williams Obstetrics, 26th ed., 2022
This is one of 3,306 questions in the MedBoardSA SMLE bank, with timed test mode, tutor mode, and progress tracking by topic.
Practise the full bank