Gestational Diabetes Mellitus

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Gestational diabetes mellitus

A state of carbohydrate intolerance, first identified during pregnancy, usually the latter half (hence no effect over organogenesis), and resolves after delivery.

Pre-gestational diabetes mellitus

Pregnancy in an overt diabetic, can be either type I or II.

Changes in carbohydrate metabolism

The carbohydrate metabolism is altered in such a way that more glucose is made available to the fetus.

Increased levels of placental hormones and cortisol increases the FFA mobilisation, causing maternal hyperglycemia. These hormones have counter-regulatory effects over the action of insulin.

Hence, GDM occurs when despite insulin secretion from pancreas is increased, but was unable to overcome the counter regulatory effects of these hormones.

Screening test

Two screening test is used worldwide.

1) Universal screening

Screening test is offered to all pregnant women.
At 24-28 weeks of gestation, glucose challenge test is done, where 50gm of glucose in solution is taken.
Blood is then taken 1 hour later to determine the glucose level and if it's 7.8 mmol/L or more, diagnostic test (OGTT) is done.

2) Selective screening

Screening test is only offered to mothers with risk factors of developing GDM.

Age > 30 years
Previous h/o of GDM
Family h/o of Diabetes mellitus
BMI > 30 (Obesity)
Previous big baby >4.5 kg
Previous fetal anomalies
Bad obstetric history

Once these risk factors are identified, a modified glucose tolerance test (MGTT) is done. Instructions given :

3 days of unrestricted diet
Fast for at least 8 hours (overnight) before the test (Best 10-12 hours)

Blood is withdrawn first -> fasting sample
Given 75gm of glucose in solution, and blood is again taken 2 hours later

If the fasting sample is 5.6 mmol/L or more and/or 2-hours post-prandial is 7.8 mmol/L or more -> GDM is confirmed

Complications of GDM and Pre-gestational diabetes

1) GDM


Pre-term labour
Operative delivery
Monilial vaginitis


Shoulder dystocia
Intrauterine death (IUD)

2) Pregestational diabetes


Hypoglycemic attacks
Diabetic vasculopathy
Difficult sugar control


Congenital anomalies

Antenatal management

Aims in antenatal management :

Good glycemic control
Antepartum surveillance
Appropriate time of delivery
Optimal neonatal support

Frequency of antenatal visits need to be increased, that is :

Every 2 weeks until 32-34 weeks of gestation
Beyond 34 weeks, weekly antenatal visits

For those with pre-gestational diabetes, during 34 weeks or more should be hospitalised for better management

Overall period of gestation shouldn't be > than 38 weeks

Blood sugar profile

If MGTT has confirmed a mother to have GDM, the first thing to do is to admit the mother to the hospital for blood sugar profile.

This is done to determine, whether dietary therapy alone or with addition of subcutaneous insulin is required.

If BSP values are normal -> only dietary therapy
If BSP values are abnormal -> Dietary therapy + SC insulin

For mothers under dietary therapy, BSP should be done every 4 weeks.
For mothers under dietary and SC insulin therapy, BSP should be done every 2 weeks.

In Muar Hospital, BSP is done following the pre-meal protocol :

Pre-breakfast, pre-lunch, pre-dinner and before sleep -> blood glucose level is assessed by glucometer.

And glucose level need to be maintained within 4-6 mmol/L

In Melaka GH, they have start using the post-meal protocol :

Post-breakfast, post-lunch, post-dinner and before sleep

Glucose level to be maintain < 7mmol/L

Dietary therapy

For those with lean body mass, intake of 30 kcal/day of calories is permitted
For those mothers who are obese, intake of only 24 kcal/day is allowed.

These calories are equally distributed in 3 meals and 3 snacks
Diet to be planned by a dietitian.

Insulin therapy

No oral hypoglycemic agents should be used during pregnancy, reasons :

a) ORH crosses the placental barrier, causing fetal hypoglycemia
b) Difficult to monitor it's level

SC insulin is usually given 20-30 min before breakfast and dinner, 2 doses.
2/3 of total dose can be given before breakfast, 1/3 of it given before dinner.

Antenatal investigations

1) Urine microscopy and culture at 28, 32 and 36 weeks of gestation
2) Urine dipstick at each visit
3) For those with pre-gestational diabetes :

Ketonuria and proteinuria -> each visit
BUSE, Creatinine, fundoscopy and HbA1c in every trimester

4) Starting from 16-20 week -> maternal alpha-fetoprotein
5) Ultrasound at 18-22 weeks of gestation -> fetal anomalies scan
6) Fetal echocardiography at 22-24 weeks of gestation -> Cardiac defects
7) Ultrasound at 3rd trimester

Amniotic fluid assessment (polyhydramnios), fetal biometry (macrosommia)

8) For those with bad obstetric history/poor glycemic control -> twice weekly NST and Biophysical profile

9) Especially for mothers with pre-gestational diabetes -> Umbilical artery doppler

Intrapartum management

MO/Specialist to decide the mode of delivery, and :

Entire labour process should not exceed 12 hours
Glucose level during labour should be maintained within 4-6 mmol/L

During active phase of labour :

Start one IV drip
2 hourly glucometer
CTG monitoring
Maintain blood glucose at 4-6 mmol/L
If it goes up to 6-8 mmol/L -> 2 IU SC insulin
If it goes up to 8-12 mmol/L -> 4 IU SC insulin
If the mother is hypoglycemic -> 5% dextrose IV infusion


All babies born from GDM mother should be referred to a Paediatrician for further observation to be done.

For LSCS :

Skip the morning dose of insulin
Infuse 5% dextrose and 5 IU insulin in 500ml of normal saline
Infusion rate for insulin -> 1.0 IU/hr
To maintain blood glucose level within 4-6 mmol/L

Category: Obstetrics Notes



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