Gestational diabetes mellitus

Last updated: January 13, 2022

Summary

Gestational diabetes mellitus is a condition of impaired glucose tolerance during pregnancy that mostly occurs in the second and third trimesters. Patients are usually asymptomatic but may present with polyhydramnios. The fetus is often large for gestational age. All pregnant women should be screened for gestational diabetes with an oral glucose challenge test. Diagnosis is confirmed with an oral glucose tolerance test (OGTT). Treatment includes glycemic control, e.g., dietary modifications and regular exercise. If glycemic control is insufficient, insulin therapy is initiated. In most cases, gestational diabetes resolves after pregnancy. However, complications may occur, including gestational hypertension, (pre)eclampsia, and development of type 2 diabetes mellitus in the mother and diabetic fetopathy and shoulder dystocia in the fetus.

Pregestational diabetes is type 1 or type 2 diabetes mellitus that is already present prior to pregnancy, and it is associated with a significantly increased risk for maternal and fetal complications during pregnancy and delivery. Management includes stringent glycemic control and close monitoring of fetal development (e.g., regular ultrasounds to screen for congenital abnormalities).

Gestational and pregestational diabetes mellitus

Features	Gestational diabetes mellitus ^[1]	Pregestational diabetes mellitus ^[2]
Definition	Impaired glucose tolerance diagnosed during pregnancy Associated with an increased risk of maternal and fetal morbidity	T1DM or T2DM that is present prior to pregnancy Associated with a significantly increased risk for maternal complications during pregnancy and delivery, and congenital malformations
Epidemiology	Occurs in 5-7% of all pregnancies Usually in the second and third trimesters (less common in the first trimester)	Observed in 1% of all pregnancies
Pathophysiology	The insulin requirement varies during pregnancy. In the first trimester, insulin sensitivity increases and there is a tendency towards hypoglycemia. In the second and third trimesters, hormonal changes trigger progressive insulin resistance that results in hyperglycemia, particularly after mealtimes.	As for T1DM and T2DM
Risk factors	Major risk factors for T2DM (see “Etiology” in “Diabetes mellitus”) Obstetric Gestational diabetes prior to pregnancy Recurrent pregnancy loss At least one birth of a child diagnosed with fetal macrosomia
Clinical features	Mothers are usually asymptomatic May present with edema; warning signs include polyhydramnios or large-for-gestational age infants (> 90^th percentile)
Screening and diagnostics	Second trimester (at 24–28 weeks) Recommended in all pregnancies Early screening (prior to 24 weeks) is recommended in women with risk factors for gestational diabetes see above). Initial screening: 50-g, one-hour oral glucose challenge test Blood glucose level should be < 135 mg/dl If positive, patients are given the 100-g oral glucose challenge test as confirmation Confirmation test: 100-g, three-hour oral glucose tolerance test (oGTT) ≥ 140 mg/dl	Maternal Baseline HbA1c Renal function (creatinine clearance, proteinuria, glucosuria) Cardiac evaluation Ophthalmic testing Monitoring fetal development Weeks 18–24: ultrasound to determine fetal age, evaluate fetal growth, screen for congenital anomalies Weeks 32–36: close surveillance with ultrasound and nonstress test Week > 36: at least once weekly ultrasound; consider amniocentesis if delivery is to be induced prior to 39 weeks of gestation
Treatment	Glycemic control Dietary modifications and regular exercise (walking) Strict blood glucose monitoring (4x daily) Insulin therapy if glycemic control is insufficient with dietary modifications Metformin and glyburide in patients who are unwilling or unable to use insulin Regular ultrasound to evaluate fetal development Consider inducing delivery at week 39–40, if glycemic control is poor or if complications occur	Stringent glycemic control (exercise, diet, insulin therapy) Delivery and postpartum Consider early delivery if the patient has poor glycemic control or preeclampsia Consider C-section if estimated fetus weight > 4500 g Intrapartum IV insulin and dextrose to avoid blood glucose fluctuations (maintain blood glucose level between 80–100 mg/dL; hourly blood glucose measurements
Complications	Maternal Gestational hypertension Preeclampsia, eclampsia, and HELLP syndrome Urinary tract infection Fetal Diabetic fetopathy Shoulder dystocia	Maternal Diabetic ketoacidosis (in T1DM), hyperosmolar hyperglycemic nonketotic coma (in T2DM) Gestational hypertension Preeclampsia, eclampsia, and HELLP syndrome Urinary tract infection Increased risk of premature birth Spontaneous abortions Postpartum hemorrhage Polyhydramnios Fetal Diabetic embryopathy (first trimester) Diabetic fetopathy (second and third trimester)
Prognosis	In most cases, gestational diabetes resolves after pregnancy. Increased risk of gestational diabetes recurring in subsequent pregnancies (∼ 50%) Increased risk of developing T2DM (up to 50% over 10 years) → screen for DM 6–12 weeks postpartum (75 g 2-hour GTT); repeat every 3 years	As for T1DM and T2DM

References

Chiefari E, Arcidiacono B, Foti D, Brunetti A. Gestational diabetes mellitus: an updated overview. J Endocrinol Invest. 2017; 40 (9): p.899-909. doi: 10.1007/s40618-016-0607-5 . | Open in Read by QxMD
ACOG Practice Bulletin No. 201. ACOG Practice Bulletin No. 201. Obstetrics & Gynecology. 2018; 132 (6): p.e228-e248. doi: 10.1097/aog.0000000000002960 . | Open in Read by QxMD

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