Glycemic response curve in pregnancy: when to do it and what food precautions the mother-to-be should follow

Glycemic response curve in pregnancy. What is it used for? When to do it? Why? And, above all, what risks and complications can be prevented with this test?

GCT stands for Glucose Challenge Test, a test for screening gestational diabetes, also known as ‘Glycemic response curve in pregnancy*’.

Which translated simply means a test that is carried out to detect women who have typical symptoms and values of gestational diabetes and to minimise maternal and foetal-neonatal risks due to excessive blood glucose.

In pregnancy, as we already know, several specific tests are carried out. Some of these are compulsory or always necessary while others are strongly recommended.

One of these is prenatal screening to find out one’s blood group and prevent problems and complications that can occur with Rh conflict (Rh-negative mother and Rh-positive father) such as haemolytic disease of the newborn (severe hyperbilirubinaemia and jaundice, Kernicterus and severe anaemia).

Anti-Rh(D) immunoprophylaxis consists in the administration of a drug to the mother-to-be in the 28th week of pregnancy that prevents the body from producing antibodies (immunoglobulin Rh0 (D)) against the Rh factor and thus prevents problems due to Rh incompatibility.

Among the other recommended examinations to assess the possible presence of gestational diabetes there is the glycemic response curve (also known as the ‘oral glucose tolerance test’ or OGTT), a very simple test that is carried out without any consequences for the mother and the baby.

This clinical test thus makes it possible to detect the presence of alterations in carbohydrate metabolism during gestation.

Glycemic response curve in pregnancy consists in measuring the blood sugar concentration before and after the oral administration of a certain amount of standard glucose solution. The test is always carried out in the morning hours and through three samples: on an empty stomach, one hour and two hours after taking a solution consisting of water and 75 grams of pure glucose. This solution – in the form of a drink – may in some cases cause discomfort to the woman; the sweetness, for example, may promote the onset of symptoms such as nausea, gastritis and vomiting. In the latter case, the test should be repeated on another day, as the values would no longer be reliable.

The test is prescribed to all mothers-to-be between 24 and 28 weeks’ gestation if there is at least one of the following risk factors:

• Familiarity with diabetes in first-degree relatives;
• Foetal macrosomia (baby weight > 4.5 kg) in previous pregnancies;
• Overweight/Obesity (BMI ≥25 kg/m2);
• Age 35 years or older;
• High-risk ethnicities (South Asia, Middle East, Caribbean).

But what is the purpose of glycemic response curve in pregnancy?

Pregnancy brings many changes in the female organism mainly due to the hormonal changes typical of this period. Some of these also affect the endocrine system. In particular, in the second trimester, there is a reduction in insulin response, resulting in an increase in circulating glucose in the body.

Thanks to the glycaemic test, it is possible to identify women who have typical symptoms and values of gestational diabetes, so that glycaemia can be kept under control and possible treatment can be started, and above all minimise maternal and foetal-neonatal risks due to excessive blood glucose increase.

It is very important to inform the mother-to-be and reassure her by telling her that, in most cases, gestational diabetes is managed through dietary and lifestyle measures.

An appropriate diet should include foods rich in calcium, iron and folic acid. The woman with gestational diabetes should adopt a low-fat, high-fibre diet. Carbohydrates such as cereals, fruit, pasta and rice should be consumed in moderation.

Here are some useful tips:

• Eat at regular times, never skip meals, avoid excesses at the weekend.
• Snacks are very important, especially in the evening, to avoid long periods of fasting.
• Choose wholegrain cereals and their derivatives, preferably in light processing.
• Limit the use of salt, foods already contain sodium.
• Limit the use of animal fat such as butter, lard and cream and prefer extra virgin olive oil instead.
• Fruit can be eaten fresh, cooked or blended without adding sugar.
• Do not consume more than 500 g in a day as it is sweet and rich in sugar (fructose).
• Avoid fruit juices, corn syrup, maple syrup, dried fruit, canned fruit, candied fruit, jams, chestnuts, bananas, grapes, persimmons, figs.
• Limit coffee intake to no more than 2 per day: caffeine is contained not only in coffee but also in tea, chocolate and cola drinks.
• Avoid sweets, desserts, cakes, candy, chocolate, snacks, etc., which in a small volume provide a lot of calories and contribute to excessive and rapid weight gain and alteration of glycaemia values.

It should be pointed out, however, that if pregnancy diabetes is not kept under control with precautions, there is an increased risk of maternal and foetal complications such as: pre-eclampsia and shoulder dystocia (difficulty in getting the shoulders out during delivery), urinary and vulvovaginal infections, foetal malformations, gestosis, pre-term delivery, miscarriage and excessive amniotic fluid.

Preparation for glycemic response curve in pregnancy starts the day before the test because the last meal eaten must be balanced (excesses but also restrictions must be avoided). On the day of the test, it is necessary to have been fasting for at least 8-10 hours and, once the test is over, the expectant mother can get back to eating as usual except for precise medical instructions and prescriptions.

It should be underlined that the values of the glycemic response curve for pregnant women are different from those of other women but, regardless of these, the report, indications and precautions will be evaluated and recommended by the gynaecologist who is monitoring the future mother’s pregnancy.

By Francesca Franceschi