Gestation refers to the period of development of an embryo to a fetus which occurs from the time of conception until birth. Gestational diabetes mellitus (GDM) also called pregnancy-induced diabetes, is glucose intolerance disorder of any kind and any level of severity which occurs or is diagnosed only during pregnancy. In order words, women with gestational diabetes have never had any form of glucose intolerance disorder before pregnancy. Because of this, GDM is a medical complication of pregnancy and affects between 7 to 10% of pregnant women worldwide.

For most women, gestational diabetes will go away immediately after delivery. But for some, it doesn’t and in this case, it is called type 2 diabetes. However, about half of the women whose gestational diabetes go away after delivery eventually develop type 2 diabetes about 5 to 10 years later. So, frequent checkups, exercise, and a healthy diet are necessary after delivery.

Causes of gestational diabetes mellitus

Insulin resistance refers to the inability of your body cells to respond well to the hormone insulin. Consequently, these cells cannot use glucose (or sugar) efficiently for energy. This causes glucose to accumulate in the blood. All pregnant women experience insulin resistance or desensitization during pregnancy. This is because, during pregnancy, several hormonal changes take place to facility the growth of the fetus. Some of these hormones affect the insulin receptors causing them to become insensitive or resistant to insulin. Hormones which cause insulin resistance during pregnancy include human placental lactogen (HPL) hormone secreted from the placenta and the growth hormones cortisol, estrogen, and progesterone. Gestational diabetes mellitus develops when insulin synthesis and secretion are insufficient to overcome the insulin resistance that naturally increases during all pregnancies.

Risk factors for gestational diabetes mellitus

Risk factors contributing to the development of gestational diabetes mellitus (GDM) include:

  • Overweight and obesity: At least 15% of cases of GDM are associated with overweight and obesity (BMI of 25 kg/m2 or above). Therefore, women of reproductive age need to keep their BMI below 25 kg/m2 through physical exercise and healthy eating.
  • Physical inactivity: Prolong sedentary behavior and decrease physical activity before and during pregnancy is a potential risk factor for developing GDM.
  • Advanced maternal age:  Women aged 35 years and above have a higher risk developing GDM and subsequent complications during pregnancy. This increases with increase in the age of the pregnant woman. Study shows that women with advanced maternal age (≥ 35 years) have a 2-3 fold risk of developing gestational diabetes and related complications when compared with those aged 20-30 years.
  • Race and ethnicity: Race, ethnicity, and country of birth influences the risk of developing GDM. Risk is lowest among non-Hispanic white women (4.2%), Blacks (4.4%), other Hispanics (5.4%) and Japanese (5.5%). But is intermediate among Koreans (6.7%), Mexicans (7.1%), Pacific Islanders (7.2%), and Chinese (7.9%). Highest risk is found among Southeast Asians (8.8%), Filipinas (9.6%) and Asian Indians (11.1%).
  • Family history of diabetes increases the chances of getting GDM by 1.5-fold.
  • Depression: Antepartum depressed also increases your chances of developing gestational diabetes by 1.54-fold.
  • Hypertension (high blood pressure): Hypertension before and during early pregnancy is associated with a 2-fold risk of developing gestational diabetes during pregnancy. The correlation between hypertension and GDM is stronger for women who are overweight.
  • Hypercholesterolaemia
  • Previously given birth to a baby weighing 4.5 kg or above
  • Previous history of GDM
  • Diseases associated with increased insulin resistance such as polycystic ovarian disease (PCOD), polycystic ovarian syndrome (PCOS), and acanthosis nigricans also increase the risk of GDM.

    Complications of gestational diabetes mellitus

    Gestational diabetes mellitus (GDM) causes both short-term and long-term complications for the mother and her baby. Complications occur if gestational diabetes is not well controlled and monitored during pregnancy.  Complications due to GDM can occur during pregnancy, a few hours to days after delivery, or several years later. The impact or level of severity will depend on how well the mother’s diabetes was controlled and monitored during pregnancy. Most women with gestational diabetes may need high-risk pregnancy care due to complications that can arise during pregnancy and childbirth.

    Short-term complications of gestational diabetes for the baby include macrosomia (baby larger than normal), shoulder dystocia, birth trauma (or injury), hypoglycemia in the immediate postpartum period, premature delivery, or stillbirth. Long-term complications for babies born to mothers with gestational diabetes include increased risk of childhood and adulthood obesity, diabetes, and cardiometabolic diseases.

    Short-term complications for a mother with gestational diabetes include hypertension, pre-eclampsia, eclampsia, cesarean delivery, stroke, kidney failure, liver problem, or birth trauma. Long-term complications include increased risk of recurrence of gestational diabetes in subsequent pregnancy and increased risk of developing type 2 diabetes.

    Short term complications

    Hypertension (high blood pressure)

    GDM increases the occurrence of hypertensive disorders during pregnancy, including chronic hypertension, gestational hypertension, pre-eclampsia, and eclampsia. Hypertensive disorders usually begin after 20 weeks of pregnancy but can start earlier. If left untreated or unmanaged, hypertension can lead to low birth weight, premature birth, stillbirth, or early labor induction for the baby. For the mother, it can lead to seizure, stroke, temporal kidney failures, liver problems, blood clotting problems, or caesarian delivery.

    Urinary tract infection

    Pregnant women with GDM have a higher risk of developing urinary tract infection. This is due to the anatomical and physiological changes which occur in the urinary tract. Also, there is suppression of the immune system caused by high blood sugar.


    Hydramnios, also called polyhydramnios or amniotic fluid disorder, is a medical condition in which excess amniotic fluid builds up during pregnancy. It may be caused by fetal anomalies, fetal infection, digestive problems that block fluid, disturbed fetal swallowing of amniotic fluid and gestational diabetes in addition to other unknown causes. At least 8% of women with GDM have mild hydramnios and as such hydramnios has been considered as an indicator to test for GDM.

    Fetal macrosomia (fetus larger than normal)

    Fetal macrosomia is a term used to describe newborn babies who are larger than normal (more than 4 kg). If maternal diabetes is not well controlled, then the baby might develop fetal macrosomia. This is because the baby is exposed to high levels of blood sugar (or glucose) from the mother. Consequently, the extra glucose is stored as body fat and results in macrosomia.

    Fetal macrosomia may complicate vaginal delivery. This includes putting the baby at risk of injury during birth or causing shoulder dystocia. It may also force the mother to give birth through cesarean delivery. There is also an increased risk of health problems after birth. This includes lower insulin sensitivity and an increased risk of obesity and diabetes in later life.

    According to the HAPO study, maternal hyperglycemia even below the diagnostic threshold of diabetes mellitus is associated with increased birth weight and macrosomia.

    Neonatal hypoglycemia

    Hypoglycemia is when blood glucose (or sugar) level is lower than normal. This may occur immediately after birth or during the first few days. Hypoglycemia in neonate is generally considered a serum glucose concentration < 40 mg/dL (2.2 mmol/L) in symptomatic term neonates, < 45 mg/dL (2.5 mmol/L) in asymptomatic term neonates between 24 hours and 48 hours of life, or < 30 mg/dL (1.7 mmol/L) in preterm neonates in the first 48 hours of life.

    Neonatal hyperglycemia occurs because, when a mother has diabetes, she exposes the fetus to high levels of glucose. The fetus responds by producing increased levels of insulin. Once the umbilical cord is cut during birth, the infusion of glucose to the neonate ceases. But there is now elevated levels of insulin produced by the baby. This high level of insulin can cause the baby sugar levels to drop drastically. It may take hours or even days for the baby to adjust its insulin levels after birth.  In most cases the baby does not show any symptom after birth but prolong or severe hypoglycemia may cause:

    • Shakiness
    • Seizures
    • Coma
    • Low body temperature (hypothermia)
    • Low heartbeat or respiratory distress
    • stop breathing (Apnea)
    • Lack of movement, energy, or weakness (lethargy)
    • Excessive sweating
    • Increase breathing (tachycardia)
    • cyanotic episodes. Causes blue tint to skin and lips
    • Not interested in feeding
    • Floppy muscles (poor muscle tone)

    Long term complications

    Mother developing type 2 diabetes

    Once you’ve had gestational diabetes, there is a 50 % chance that you will develop type 2 diabetes in the next 5 to 10 years and this may last for a lifetime. However, it can be prevented through regular exercise, maintaining a healthy body weight (≤ 25 kg/m2), eating healthy, and going for frequent checkups.

    Children developing disorder of glucose metabolism and adiposity (becoming obese)

    There are very limited long-term effects on babies whose mothers had gestational diabetes. However, there is a great risk of becoming obese or developing diabetes at a later stage in life. To minimize long-term complications for your baby, breast feed them for at least 3 months. Also, do not give them any cow milk or cereal-based product within this time. Again, encourage them to eat healthy, exercise regularly, and maintain a healthy body wight.

    Cardiometabolic diseases

    Studies have shown that children born to mothers with GDM had an increased risk of disease of the circulatory system. This includes rheumatic fever, hypertensive disease, ischaemic heart disease, disease of pulmonary circulation, other forms of heart disease, cerebrovascular disease and diseases of arteries, veins etc.

    Screening and diagnosis for gestational diabetes mellitus

    When to screen for gestational diabetes

    Gestational diabetes is screened or tested between 24 and 28 weeks of pregnancy. This is because insulin resistance increases during this period due to high levels of growth hormones such cortisol, estrogen, and progesterone. An increase in insulin resistance will cause increase glucose levels for women whose body cannot produce enough insulin to adapt to the increase in resistance.

    However, gestational diabetes can still be tested during the first prenatal visit if the mother is at high risk of developing diabetes. High risk factors will include mother being overweight or obese before pregnancy, older than 35 years, has high blood pressure, has sugar in pee during prenatal visit, has had gestational diabetes during previous pregnancy, or has a family history of gestational diabetes. Additionally, gestational diabetes can still be tested even after 28 weeks of pregnancy. Women who previously tested negative for glucose tolerance test are retested between 32 and 36 weeks. This is because insulin resistance can worsen during this period.

    GDM is diagnosed at 16.3% within 16 weeks of gestation, 22.4% between 17 and 23 weeks of gestation and 61.3% after 23 weeks of gestation.  Therefore, testing too early may not be helpful for all patients. But testing too late might also limit the time for medical interventions aimed at preventing complications associated with GDM. It is therefore recommended that all pregnant women should be screened for diabetes on their first prenatal visit using fasting plasma glucose, HbA1C, or random plasma glucose.

    Screening and diagnosis of gestational diabetes

    Because of complications or adverse effects of GDM for both mother and child, early and accurate diagnosis is of uttermost importance. Unfortunately, there is no universally agreed method for screening and diagnosing gestational diabetes. Therefore, different criteria are being used as proposed by the world health organization (WHO), American diabetes association (ADA), international association of diabetes and pregnancy study groups (IADPSG), diabetes in pregnancy study group India (DIPSI), and American college of obstetricians and gynecologists (ACOG).

    World Health Organization (WHO) 1999 Criteria

    In 1999 the WHO put forth the following criteria for screening and diagnosing gestational diabetes:

    • During the first trimester (weeks 1 to 13) and early second trimester (week 14 to 27) fasting blood glucose and postprandial glucose concentrations are normally lower for pregnant women than in normal non-pregnant women. Therefore, elevated levels of blood glucose at this time may indicate diabetes mellitus which antedated the pregnancy.
    • GDM should be tested between week 24 and 28 of pregnancy using a standard oral glucose tolerance test (OGTT) in a one-step procedure.
    • OGTT should be carried out with 75 g anhydrous glucose in 250-300ml of water after an overnight fasting of 8 to 14 hours. Fasting plasm glucose (FPG) and glucose levels at 2 hours are measured. FPG equal to or greater than 126 mg/dL (7.0 mmol/L) and 2-hour Blood glucose equal to or greater than 140 mg/dL (7.8 mmol/L) is diagnostic of GDM. The test should then be repeated after 6 weeks or more postdelivery.
    • This test is mostly used in developing countries since it involves a one-step procedure.

    The WHO 1999 criteria used a single glucose value to diagnose GDM.  But FPG level ≥ 7.0 mmol/L is too high and has led some groups to use only 2 hours plasma glucose measurement without FPG while others used both measurements. In 2013, the WHO then recommended new diagnostic criteria. The criteria states that GDM should be diagnosed at any time in pregnancy if one or more of the following abnormalities are met, fasting plasma glucose 92 – 125 mg/dl (5.1 – 6.9 mmol/L), one hour plasma glucose ≥ 180mg/dl (10.0mmol/L), 2-hour glucose 153-199 mg/dl (8.5 -11 mmol/L) after overnight fasting with 75 g glucose.

     Diabetes in pregnancy study group India (DIPSI) Criteria

    Asian women particularly Indians have a genetic predisposition to metabolic syndrome which disposes them to higher risk of developing GDM.  Due to the higher prevalence and diversity of India population, DIPSI recommends a universal screening and a single step diagnosis of GDM. DIPSI recommends non-fasting OGTT with 75 g of anhydrous glucose in 250-300 mL of water with a cut-off of ≥ 140 mg/dl after 2-hours. Although it is easier and more economical, it has a low sensitivity. This leaves a lot of pregnant women undiagnosed or gives false positive results. It is therefore better as a screening test rather than a diagnostic test.

    International Association of Diabetes and Pregnancy Study Group (IADPSG) Criteria

    For IADPSG criteria an OGTT is done in the fasting state using 75 g of anhydrous glucose at 24-28 weeks Fasting blood glucose and blood glucose at 1-hour and 2-hour postprandial are measured.  GDM is diagnosed if any one of the following cut-offs is met i.e. fasting plasma glucose ≥ 92 mg/dl (≥ 5.2 mmol/l) or 1-hour ≥ 180 mg/dl (≥ 10 mmol/l) or 2-hour ≥ 153mg/dl (≥ 8.5 mmol/l). The WHO and ADA have endorsed this criteria or approach. But it has 2 main disadvantages. Firstly, it uses only a single glucose value to confirm diagnosis, and this usually leads to false positive. Secondly, it uses a low fasting plasma glucose cut-off which may also result to false positive.

    American Congress of Obstetricians and Gynecologists (ACOG) Criteria

    The ACOG criteria is a two step-procedure and diagnosis is confirmed using two abnormal glucose values. Firstly, GDM is screened using a non-fasting glucose challenge test with 50 g of anhydrous glucose and measured at 1-hour postprandial. Blood glucose values ≥ 140 mg/dl (7.8 mmol/L) is said to be abnormal. This is then followed by a 3-hour OGTT to confirm diagnosis carried out after an overnight fast with 100 g of glucose load. GDM is diagnosed if two or more of the following values are correct:

    • Fasting serum glucose ≥ 95 mg/dl (5.5 mmol/l)
    • 1-hour serum glucose ≥ 180 mg/dl (10.0 mmol/l)
    • 2-hour serum glucose ≥ 155 mg/dl (8.6 mmol/l)
    • 3-hour serum glucose ≥ 140 mg/dl (7.8 mmol/l)

    American Diabetes Association (ADA) 2015 Criteria

    ADA recommends both the IADPSG and ACOG criteria for diagnosis of GDM.  But it supports early screening for women with high risk of developing GDM rather than universal screening for all women. The IADPSG criteria is the only outcome-based criteria. IADPSG can diagnose and treat GDM earlier, thereby reducing the fetal and maternal complications associated with GDM. The ACOG criteria is preferred by most healthcare providers.

    If you are diagnosed with gestational diabetes, then you will be tested for diabetes 4 to 12 weeks after delivery. Thereafter, you will be screened after every 3 years for the rest of your life.

    How to treat and manage gestational diabetes mellitus

    Treatment of gestation diabetes aims at keeping blood sugar levels within normal range.  It involves three main interventions including lifestyle changes, medications, and blood sugar monitoring. Women whose diabetes are well managed and controlled during pregnancy, deliver safely and give birth to healthy babies.

    Lifestyle changes

    Lifestyle changes involve having a healthy diet and staying physically active.  Your diet should focus more on fruits, vegetables, whole grain, lean protein, foods high in fiber and nutrition and low in calories. Avoid refined carbohydrates, sweets and processed foods or meat.  Stay physically active through housework, gardening, walking, cycling or swimming. Also perform some minor exercises for at least 30 minutes every day. Check with your healthcare provider before starting any form of exercise regime.

    Blood sugar monitoring

    Proper control of blood sugar levels is very crucial in avoiding short-term and long-term complications. It is therefore important to maintain your blood sugar levels within targets. This is best achieved by understanding how your blood sugar levels change after a meal, an activity or after taking a medication. Blood sugar should be measured before a meal, after a meal, a medication, or an exercise until you fully understand how your body works if possible.

    The following blood sugar target values are recommended:

    • Before a meal (preprandial): 95 mg/dl (5.3 mmol/L) or less
    • One hour after a meal (postprandial): 140 mg/dl (7.8 mmol/L) or less
    • Two hours after a meal (postprandial): 120 mg/dl (6.7 mmol/L) or less

    The HA1C test is also used to monitor blood sugar levels and will give average levels of blood glucose over the past three months. Pregnant women need to target an A1C value of 6% or less.


    Most women are not able to meet their blood sugar target through diet and exercise. They require pharmacological intervention which includes insulin injections and oral glucose-lowering drugs such as metformin and glibenclamide. Although insulin injection is effective, there seems to be increasing evidence that glucose lowering drugs may have adverse long-term outcomes on children and adults exposed to the drugs in utero. Therefore, most healthcare providers prefer injectable insulin.

    GDM normally goes away after delivery. But in some few cases, the women had type 1 or type 2 diabetes which was uncovered only during pregnancy. Such women will need to proceed with treatment even after delivery.

    Does eating too much sugar cause gestational diabetes?

    It is not recommended to eat too much sugar during pregnancy. Too much sugar during pregnancy contributes to an excessive gestational weight gain which increases your risk of developing complications such as gestational diabetes, pre-eclampsia, preterm birth, and delivery complications. Too much sugar can also cause your unborn baby to get too big or your baby can suffer long-term complications such as overweight or obesity. In addition, too much sugar raises your blood sugar level which contributes to unpleasant symptoms such as tiredness, increase thirst, frequent urination, dry mouth, and genital itching.