Gestational Diabetes

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Gestational diabetes mellitus (GDM)\: glucose intolerance with onset during pregnancy, a
Aetiology\: involves placental hormones increasing insulin resistance; pancreatic beta cells fail to compensate, causing
maternal hyperglycaemia.
Risk factors\: BMI >30, previous macrosomic baby, previous GDM, family history of diabetes, certain ethnicities (South Asian,
Black, Middle Eastern).
Symptoms\: usually asymptomatic, but may include polyuria, polydipsia, lethargy, dry mouth, visual disturbances.
Diagnosis\: oral glucose tolerance test (OGTT); GDM diagnosed if fasting plasma glucose ≥5.6 mmol/L or 2-hour glucose
≥7.8 mmol/L.
Management\: includes lifestyle changes (diet, exercise), metformin if glucose targets unmet, and insulin if severe
hyperglycaemia persists.
Complications (maternal)\: increased risk of hypertension, caesarean section, future type 2 diabetes, GDM in future
pregnancies.
Complications (neonatal)\: macrosomia, neonatal hypoglycaemia, obesity, type 2 diabetes, stillbirth.
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A comprehensive topic overview

Introduction

Gestational diabetes mellitus (GDM) is a metabolic condition that occurs during pregnancy and can signi
future health of both the mother and the newborn. It is de
pregnancy and occurs in 2-5% of pregnancies.
1-2
It is important to note that gestational diabetes is a separate condition from diabetes in pregnancy, which also needs
careful management to avoid complications for the mother and newborn. Diabetes in pregnancy includes pre-existing
diabetes (type 1 or type 2), diagnosed before pregnancy.
3

Aetiology

The pathophysiology of GDM begins with the hormonal and metabolic changes that occur during pregnancy. During
normal pregnancy, hormones such as human placental lactogen and oestrogen physiologically increase insulin
resistance. This adaptation ensures that glucose is available for the growing fetus. In GDM, this process becomes
dysregulated.
1, 3
The placenta releases several substances, such as adipokines (including leptin and adiponectin), tumour necrosis factor-
alpha, and other cytokines. These substances impair insulin signalling pathways in maternal tissues, such as muscle and
adipose tissue. Maternal cells become less responsive to insulin, increasing blood glucose levels.
2-3
The pancreas attempts to compensate for elevated glucose levels by increasing insulin production. However, in GDM, this
compensatory mechanism is insu
blood glucose levels rise, leading to hyperglycaemia.
3The fetus then produces more insulin to manage the fetal hyperglycaemia, which can cause its own set of complications,
including macrosomia and neonatal hypoglycaemia.
2
Although GDM typically resolves after delivery, individuals with a history of GDM are at increased risk of developing type 2
diabetes later in life due to persistent insulin resistance.
1-3

Risk factors

Risk factors for developing GDM include\:
4-5
BMI >30 kg/m
2
Previous macrosomic baby (weighing ≥4.5 kg)
Previous GDM
Family history of diabetes (‑degree relative with diabetes)
Ethnicity with a high prevalence of diabetes, e.g. South Asian, Black, African-Caribbean, or Middle Eastern

Clinical features

History
GDM is often asymptomatic and is typically diagnosed during routine screening. Some women may experience
symptoms similar to those of hyperglycaemia, though these symptoms can overlap with normal pregnancy changes.
3-5
These include\:
Polyuria\: increased urination due to hyperglycaemia causing osmotic diuresis
Polydipsia\: excessive thirst resulting from dehydration caused by polyuria
Lethargy
Dry mouth
Visual disturbances\: temporary vision changes due to high blood glucose a
Clinical examination
Speci
Genital candidiasis\: vulvovaginal erythema, swelling, itching and discharge
Hypertension or oedema\: preeclampsia may be associated with GDM

Di

Di
Type 1 diabetes mellitus (T1DM)\: may present with similar symptoms, though unlikely to be diagnosed during
pregnancy
Type 2 diabetes mellitus (T2DM)\: may present with similar symptoms and
postpartum, the diagnosis may be T2DM
Polycystic ovary syndrome (PCOS)\: can present with insulin resistance
Stress-induced hyperglycaemia\: short periods of elevated blood glucose levels which usually resolve within hours or
days

Investigations

Bedside investigations
Routine urinalysis during antenatal care can help detect glycosuria.
1, 4-5
Further testing for GDM should be considered if testing shows\:
Glycosuria of 2+ or above on one occasion, orGlycosuria of 1+ or above on two or more occasions
Laboratory investigations
The oral glucose tolerance test (OGTT) should be used to test for GDM in women with risk factors or the presence of
signi
should be o
The oral glucose tolerance test
The OGTT involves an initial overnight fast and morning blood glucose measurement. The patient is then given a 75 g
glucose solution to drink, followed by a 2-hour period of rest and fasting, avoiding other food, drink or smoking.
4
A repeat blood glucose measurement is taken 2 hours after ingestion.

Diagnosis

GDM is diagnosed if the woman has either\:
Fasting plasma glucose ≥5.6 mmol/L or
2-hour plasma glucose level ≥7.8 mmol/L
Within 1 week of being diagnosed with GDM, women should be o
antenatal clinic.
4

Management

If GDM is diagnosed, a multidisciplinary team, including an obstetrician, dietitian, and diabetic nurse, will manage the
woman's care.
Antenatal care
Monitoring
Regular blood glucose monitoring (4-6 times daily), including fasting and postprandial levels
Frequent follow-up appointments to adjust treatment and manage complications
Patient education
potential treatments
perinatal death
Explain the short- and long-term implications of GDM for both mother and baby, including the impact on driving and
Emphasise that good blood glucose control reduces complications such as fetal macrosomia, birth trauma, and
Educate on self-monitoring of blood glucose and adherence to treatment
Lifestyle measures
Lifestyle advice should be o
diagnosis, a trial of diet and exercise should be o
4-5
Diet\: all women should be referred to a dietician to discuss a healthy, low glycaemic index diet
Exercise\: encourage regular physical activity tailored to the patient
Weight loss (if applicable)\: discuss safe weight management strategies
Medical management

Metformin

If blood glucose targets are not met within 2 weeks of lifestyle modi
Metformin is safe in pregnancy to manage GDM.Insulin
For women with a fasting blood glucose ≥7 mmol/L at diagnosis, or where blood glucose targets are not met with
metformin, insulin should be started. This is typically a basal-bolus regime with long- and short-acting insulin.
4
Metformin can be used alongside insulin to support glycaemic control.
Intrapartum care
Continuous fetal monitoring during labour is recommended, especially if the baby is large for gestational age
Plan for potential complications, such as shoulder dystocia or the need for a caesarean section
Postpartum care
E
ensuring proper follow-up. For neonates, it includes appropriate monitoring and care based on their risk factors.
Maternal care
1, 4
After delivery, it’s essential to adjust diabetes management. Insulin and metformin should be stopped, and monitoring for
persistent hyperglycaemia should be performed before discharge.
A repeat fasting plasma glucose is recommended between 6 - 13 weeks postpartum. Further testing or referral to the NHS
Diabetes Prevention Programme may be necessary based on results. Even if initial postnatal tests are normal, an annual
HbA1c is advised to monitor long-term blood glucose.
Women with a history of GDM should consider early self-monitoring or an OGTT in future pregnancies.
Neonatal care
4
Newborns from mothers with GDM should be delivered in hospitals with 24-hour advanced neonatal resuscitation
services. Their blood glucose levels should be monitored closely within the
discharged to community care until they are at least 24 hours old, have stable blood glucose levels, and are feeding
adequately.
An echocardiogram may be needed if there are signs of congenital heart disease or cardiomyopathy. Newborns showing
signi
may need admission to the neonatal intensive care unit (NICU).
Preventing and managing hypoglycaemia4
Newborns should start feeding within 30 minutes of birth and continue every 2-3 hours to maintain glucose levels
above 2.0 mmol/L. If blood glucose remains low despite feeding or abnormal signs are present, nasogastric feeding
or intravenous glucose may be needed.
Clinical signs of hypoglycaemia, such as sweating, feeding di
hypothermia, requires immediate blood glucose measurement and intravenous glucose if hypoglycaemic.

Complications

Maternal risks
Complications experienced by the mother may include\:
1, 4-5
Hypertension\: increased risk of developing pregnancy-induced hypertension or preeclampsia
Caesarean delivery\: higher likelihood of requiring a caesarean section due to complications such as macrosomia
Type 2 diabetes\: increased risk of developing type 2 diabetes after delivery. Postnatal follow-up with monitoring of
HbA1c levels is essential, and lifestyle interventions should be o
Future pregnancies\: higher risk of GDM in subsequent pregnancies. Regular postnatal follow-up with a GP is crucial for
managing future pregnancy risks and monitoring glucose levelsNeonatal risks
Complications experienced by the neonate may include\:
1, 4-5
Macrosomia\: increased risk of a baby being large for gestational age (>4.5 kg), which can lead to shoulder dystocia and
other delivery complications
Neonatal hypoglycaemia\: risk of low blood sugar in the
treatment
Metabolic syndrome\: higher likelihood of obesity and type 2 diabetes later in life
Stillbirth\: elevated risk, particularly if the mother’s blood glucose is poorly controlled

References

Collins S, Arulkumaran S, Hayes K, Jackson S, Impey L. Oxford Handbook of Obstetrics and Gynaecology. United Kingdom.\:
Oxford University Press.; 2013.
Xu P, Dong S, Wu L, et al. Maternal and Placental DNA Methylation Changes Associated with the Pathogenesis of
Gestational Diabetes Mellitus. Nutrients. Dec 23 2022;15(1)
NHS.UK. Gestational diabetes. 2022. Available from\: [LINK].
NICE Guidelines [NG3]. Diabetes in pregnancy\: management from preconception to the postnatal period. 2015. Available
from\: [LINK].
Royal College of Obstetricians and Gynaecologists. Gestational diabetes. 2021. Available from\: [LINK].

Reviewer

Professor Michael Geary
Consultant in Obstetrics & Gynaecology

Related notes

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Antenatal Screening for Down’s Syndrome
Antepartum Haemorrhage (APH)
Breech Presentation
Caesarean Section

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Contents

Introduction
Aetiology
Risk factors
Clinical features
DiSource\: geekymedics.com