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Preexisting diabetes mellitus in pregnancy
Other Resources UpToDate PubMed

Preexisting diabetes mellitus in pregnancy

Contributors: Ericka Scott, Jordana Gilman MD, Mitchell Linder MD
Other Resources UpToDate PubMed


An estimated 34 million adults are living with diabetes in the United States, and of those, 14.9 million are women. The prevalence of diabetes mellitus in women of reproductive age is estimated at 3.1%-6.8%.

Type 1 diabetes is caused by insulin deficiency following autoimmune T-cell mediated destruction of pancreatic beta cells. It is typically diagnosed in childhood, but it accounts for a quarter of new diabetes cases in adults. These patients become insulin dependent. Risk factors include having a close relative with type 1 diabetes and non-Hispanic White or Black race / ethnicity.

Type 2 diabetes is typically diagnosed in adults and is related to obesity and peripheral insulin resistance. While obesity is the biggest risk factor for type 2 diabetes, genetics also plays a strong role. Type 2 diabetes is the most common form of pregestational diabetes.

Type 1 and type 2 diabetes incidence has increased in recent years, in part due to increasing obesity in the United States. Incidence varies by race and ethnicity. Some studies suggest that non-Hispanic White and Asian individuals have lower rates of diabetes. Native American individuals have a higher rate of type 2 diabetes.

Certain exposures may increase the risk of type 2 diabetes. These include:
  • Chronic exposure to arsenic in drinking water.
  • Exposure to bisphenol A, which is found in hard plastics.
  • Chronic exposure to pesticides.
Pregestational diabetes is observed in 1%-2% of pregnancies. Not all women with preexisting diabetes mellitus will show classic symptoms, making preventative care an important component of diagnosis when associated with pregnancy.

The diagnosis of pregestational diabetes is easily made preconception, in the first trimester, or in the early second trimester. There is no consensus on diagnosis in the late second trimester or third trimester, due to inability to distinguish from gestational diabetes at that time.


O24.319 – Unspecified pre-existing diabetes mellitus in pregnancy, unspecified trimester

609563008 – Pre-existing diabetes mellitus in pregnancy

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Differential Diagnosis & Pitfalls

  • Endocrinopathies occur due to abnormal hormone levels, such as epinephrine, cortisol, and growth hormone. Primary oversecretion of these hormones can result in secondary diabetes mellitus.
    • Cushing disease is caused by too much cortisol in the body leading to increased blood pressure and blood glucose. Diabetes secondary to Cushing disease is common and should be distinguished from primary diabetes mellitus by laboratory tests that test cortisol levels. Symptoms most associated with Cushing disease include hirsutism, round facies, virilization, progressive obesity, and striae.
    • Acromegaly tends to present initially with headache, vision loss, galactorrhea, and tissue overgrowth due to the excess of growth hormone. Acromegaly can cause secondary diabetes mellitus later in the disease but rarely without initial signs / symptoms of the disease.
    • Hypothyroidism affects many systems leading to cardiovascular, hematologic, neurologic, and metabolic dysfunction. Hypothyroidism can lead to hyperlipidemia, which is associated with type 2 diabetes. Thyroid dysfunction is important to consider when evaluating a patient with metabolic derangements, and thyroid studies should be obtained.
  • Drug-induced symptoms due to corticosteroids – Corticosteroids can induce hyperglycemia, cause the patient to gain weight, and exhibit moon facies.
  • Gestational diabetes if identified in the late second trimester or third trimester. It is difficult to distinguish, but hyperglycemia is treated the same way in both conditions – with insulin. Repeat a 2-hour glucose tolerance test in the postpartum period to clarify the diagnosis.
  • Infection (particularly when patient is presenting with DKA) – Infection can also be an inciting event for type 1 diabetes and for DKA. If a patient is febrile or has other systemic signs of infection, an infectious workup should be performed and a search for a source should be undertaken.
  • Severe illness can induce transient hyperglycemia known as "stress hyperglycemia." In most of these patients, diabetes will later be diagnosed. They should receive a follow-up after recovering from their acute illness to evaluate for persistence of hyperglycemia.

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Last Reviewed:02/14/2022
Last Updated:02/15/2022
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Preexisting diabetes mellitus in pregnancy
A medical illustration showing key findings of Preexisting diabetes mellitus in pregnancy (Type 1 Diabetes Mellitus) : Hyperglycemia, Polyuria, Polydipsia, Lethargy, Blurry vision
Copyright © 2023 VisualDx®. All rights reserved.