Gestational diabetes and diabetes in pregnancy: screening and care
In brief
Gestational diabetes is a rise in blood sugar that appears or is first detected during pregnancy. In France, it is screened for in women with risk factors, according to the 2010 CNGOF–SFD consensus, with a fasting blood sugar test in the first trimester and then an oral glucose tolerance test (OGTT) between 24 and 28 weeks of pregnancy; the diagnosis is made from a fasting level of 0.92 g/L (5.1 mmol/L). It is treated first with diet and physical activity, then with insulin if needed. Diabetes known before pregnancy requires preparation before conception.
What is the difference between gestational diabetes and pre-existing diabetes?
During pregnancy, hormones from the placenta make the body less sensitive to insulin, especially from the second trimester. The pancreas compensates by producing more insulin. When it cannot keep up, blood sugar rises: this is gestational diabetes.
| Situation | When is it found? | Main concern |
|---|---|---|
| Gestational diabetes | During pregnancy, usually in the second or third trimester | Excessive growth of the baby, pre-eclampsia, low blood sugar in the newborn; risk of type 2 diabetes later in life |
| Undiagnosed type 2 diabetes | Very high blood sugar from early pregnancy | It was present before pregnancy; it continues afterwards and is managed as type 2 diabetes |
| Known type 1 or type 2 diabetes | Before pregnancy | Risk of miscarriage and birth defects if blood sugar is poorly controlled at conception |
The distinction matters: gestational diabetes on its own does not increase the risk of birth defects, unlike pre-existing diabetes that is poorly controlled in early pregnancy.
Who should be tested for gestational diabetes and how?
In France, the 2010 guidelines from the French College of Gynaecologists and Obstetricians (CNGOF) and the French-speaking Diabetes Society (SFD) recommend targeted screening for women with at least one risk factor:
- age 35 or over;
- body mass index (BMI) of 25 kg/m² or more before pregnancy;
- diabetes in a first-degree relative (father, mother, brother, sister);
- gestational diabetes in a previous pregnancy;
- a previous baby with a high birth weight (macrosomia).
The tests
- In the first trimester: a fasting blood sugar test. A value of 0.92 g/L (5.1 mmol/L) or more is enough to diagnose gestational diabetes; a value of 1.26 g/L (7.0 mmol/L) or more suggests pre-existing type 2 diabetes.
- Between 24 and 28 weeks of pregnancy (weeks of amenorrhoea), if the early fasting test was normal: an oral glucose tolerance test (OGTT) with 75 g of glucose and three blood samples. The diagnosis is made if at least one value reaches the threshold: 0.92 g/L (5.1 mmol/L) fasting, 1.80 g/L (10.0 mmol/L) at 1 hour or 1.53 g/L (8.5 mmol/L) at 2 hours.
The O'Sullivan test (50 g of glucose) is no longer recommended in France. During pregnancy, excess amniotic fluid or a large baby on ultrasound may also lead to an OGTT, even in the third trimester.
These thresholds come from the international HAPO study. It showed that complications increase steadily with the mother's blood sugar, with no clear cut-off.
What are the risks of gestational diabetes for mother and baby?
For the baby
- Macrosomia: excess sugar crosses the placenta and makes the baby grow larger. The main risk is shoulder dystocia (shoulders getting stuck during birth).
- Low blood sugar in the newborn in the hours after birth, which is why the baby's blood sugar is checked.
- Jaundice and breathing difficulties, more common when diabetes is poorly controlled.
- With pre-existing diabetes poorly controlled in early pregnancy: miscarriage and birth defects, particularly heart defects.
For the mother
- High blood pressure and pre-eclampsia.
- A higher chance of caesarean section.
- Infections, especially urinary infections.
- With pre-existing diabetes: possible worsening of retinopathy, hypos on insulin, ketoacidosis in type 1 diabetes.
- In the long term, after gestational diabetes: a risk of type 2 diabetes about seven times higher than in women whose blood sugar was normal during pregnancy, according to a meta-analysis published in The Lancet.
How is gestational diabetes treated?
The aim is to bring blood sugar as close to normal as possible. Treatment follows three steps.
- Adapted diet: carbohydrates spread over three meals and two or three snacks, limited fast-acting sugars, calorie intake adjusted to your weight. Seeing a dietitian is advised. See also our advice on nutrition during pregnancy.
- Regular physical activity suited to you, such as walking, if there is no obstetric reason to avoid it.
- Insulin if targets are not reached after 7 to 10 days of dietary measures. In France, it is the recommended medicine during pregnancy; oral diabetes tablets are not recommended as first-line treatment.
You check your blood sugar with a finger-prick test, usually fasting and after meals. The targets suggested by the CNGOF and SFD are a fasting blood sugar below 0.95 g/L (5.3 mmol/L) and a blood sugar 2 hours after meals below 1.20 g/L (6.7 mmol/L). Your own targets and how often to test are explained during consultation.
How should I prepare for pregnancy with type 1 or type 2 diabetes?
With known diabetes, pregnancy needs to be planned. Well-controlled blood sugar for several months before conception reduces the risk of miscarriage and birth defects. A pre-conception consultation allows you to:
- aim for an HbA1c (glycated haemoglobin) as close to normal as possible, with your diabetes specialist;
- replace treatments that should not be used in pregnancy; in type 2 diabetes, tablets are usually replaced by insulin;
- have an eye examination and kidney tests;
- start folic acid before conception, as prescribed by your doctor.
During pregnancy, follow-up is frequent and shared between the obstetrician and the diabetes specialist: blood sugar self-monitoring several times a day, frequent insulin dose adjustments as needs change through the trimesters, growth scans and eye checks. Obstetric follow-up takes place at the practice, in liaison with your diabetes specialist, and the birth is planned at Maternité Sainte-Félicité (Paris 15th) or at Clinique Sainte-Thérèse (Paris 17th).
When should I go to the maternity emergency department?
Go to the maternity emergency department, or call 15 (SAMU, the French emergency medical service) or 112 in France, or your local emergency number, if you feel seriously unwell, or if you notice:
- fewer movements from the baby, or none;
- a severe headache, problems with your vision, pain under the ribs or high blood pressure (signs of pre-eclampsia);
- regular contractions before 37 weeks, leaking fluid or bleeding;
- a fever or burning when passing urine with back pain;
- on insulin: a severe hypo with feeling faint, confusion or loss of consciousness (those around you should call 15);
- in type 1 diabetes: very high blood sugar with nausea, vomiting, intense thirst or ketones in the urine or blood.
What happens at the birth and after with gestational diabetes?
Gestational diabetes that is well controlled, by diet alone or with insulin, and has no effect on the baby does not usually change how the birth is managed. If it is poorly controlled or affects the baby, induction or a caesarean section may be discussed case by case, taking into account the estimated weight, blood sugar control and your history.
After the birth:
- the baby has blood sugar checks and is fed early; breastfeeding is encouraged;
- with gestational diabetes, insulin is stopped and blood sugar is checked over the following days;
- screening for type 2 diabetes (fasting blood sugar or OGTT) is recommended at the postnatal check, then every 1 to 3 years depending on risk factors;
- keeping to a balanced diet, physical activity and a stable weight reduces the risk of diabetes later on;
- in a future pregnancy, blood sugar is checked from the first trimester.
Frequently asked questions
Does gestational diabetes go away after the birth?
In most cases, yes: blood sugar returns to normal in the days after the birth. However, the risk of type 2 diabetes remains higher for years, which is why a test is done at the postnatal check, followed by screening every 1 to 3 years.
Is insulin dangerous for the baby?
No. Injected insulin does not cross the placenta to any significant extent. It normalises your blood sugar, which protects the baby from excessive growth.
Can I breastfeed after gestational diabetes?
Yes, breastfeeding is encouraged. It is compatible with the newborn's monitoring and may have a beneficial effect on the mother's metabolism.
Do I have to cut out sugar completely with gestational diabetes?
No. Carbohydrates are still needed for the baby and the mother. The aim is to spread them across the day, choose low glycaemic index foods and limit fast-acting sugars.
Which blood sugar levels define gestational diabetes?
According to the 2010 CNGOF–SFD consensus, the diagnosis is made if your fasting blood sugar is 0.92 g/L (5.1 mmol/L) or more, or if a single value of the 75 g OGTT reaches the threshold: 0.92 g/L (5.1 mmol/L) fasting, 1.80 g/L (10.0 mmol/L) at 1 hour or 1.53 g/L (8.5 mmol/L) at 2 hours.
References
- Vambergue A. Expert consensus on gestational diabetes mellitus.. Diabetes Metab, 2010. doi:10.1016/j.diabet.2010.11.003 — PMID 21163415
- HAPO Study Cooperative Research Group, Metzger BE, et al. Hyperglycemia and adverse pregnancy outcomes.. N Engl J Med, 2008. doi:10.1056/NEJMoa0707943 — PMID 18463375
- Bellamy L, et al. Type 2 diabetes mellitus after gestational diabetes: a systematic review and meta-analysis.. Lancet, 2009. doi:10.1016/S0140-6736(09)60731-5 — PMID 19465232
Dr Olivier KadochObstetrician-gynaecologist and gynaecological surgeon in Paris (16th and 5th arrondissements). Former chef de clinique-assistant (senior registrar) at the Paris public hospitals (AP-HP); individually accredited by the French National Authority for Health (HAS). RPPS 10003957809. Background and practice locations
A question about your situation?Appointments at the practice or by video consultation, usually within one week to 10 days.
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