Definition:

Gestational diabetes is defined as a carbohydrate intolerance that can be of varying severity and that is initiated or first identified during pregnancy. Gestational diabetes is diagnosed in 9-14% of pregnant women. The criteria used for diagnosis are pregnancy-specific and differ from those used for the diagnosis of diabetes or glucose intolerance outside of pregnancy.
The American Diabetes Association recommends that pregnant women be screened for gestational diabetes at 24-28 weeks of gestation with a 50 g oral glucose overload test and 1 hour blood glucose determination, which is done at any time of day and without regard to the time since the last meal. If the plasma glucose concentration is 140 mg/dl (7.8 mmol/l), an oral glucose tolerance test (OGTT) should be performed with 100 g glucose and determination of blood glucose per hour for up to 3 hours.
In very high-risk women, the oral glucose tolerance test can be passed directly, without the preliminary screening step. It is performed after one night on an 8-14 hour fast and after 3 days of carbohydrate overload.
The determination of glucose with test strips and reflectmeters is not recommended for the 50 g. to 1 hour overload test or for the 100 g and 3 hour OGTT, as the accuracy of this method is relatively low compared to standard laboratory analyses.
Objective:
Sometimes a patient initially presents with diabetic ketoacidosis, these patients are likely to have previously undiagnosed type 1 diabetes mellitus. Most women with gestational diabetes do not usually have such intense hyperglycaemia that it can endanger the health and well-being of the mother.
Consequently, the issues of immediate are concerned around the health and development of the foetus. However, gestational diabetes is an important risk factor for the subsequent onset of diabetes.

-Fetal morbidity and mortality

Recent series of pregnancies with gestational diabetes diagnosed and treated in the context of modern neonatology describe significantly high perinatal mortality rates. Fetal macrosomia (increased weight) and other fetal alterations continue to be important problems in these pregnancies.
The mechanism underlying the above problems appears to be fetal hyperinsulinemia as described by Pedersen’s hypothesis, i.e. maternal hyperglycaemia, fetal hyperglycaemia, fetal hyperinsulinemia, macrosomia, fetal death, neonatal hypoglycaemia.
Since glucose easily crosses the placenta by diffusion, maternal hyperglycaemia, even if mild, is transmitted to the fetus. The fetal pancreas may be induced to secrete insulin by maternal hyperglycaemia.
Glucose testing detects gestational diabetes, an alteration in glucose metabolism that sometimes occurs in pregnancy, usually in the second half, when gestational hormones hinder the action of insulin and cause elevated blood glucose concentrations, especially after meals.
It is characterized by a difficulty in the use of carbohydrates by the body and occurs more frequently in pregnant women over 30 years or with a family history of diabetes, obesity or previous pregnancies with gestational diabetes.

-When to perform the test:

It is a type of diabetes that does not present symptoms and that is why between 24 and 28 weeks of pregnancy all pregnant women are given the O’Sullivan test, an ambulatory test with the aim of identifying if they have the possibility of suffering from this alteration, which would be confirmed later with the glucose test.
Gestational diabetes is an excess of sugar in the blood that some women (and especially Latins, African Americans, Amerindians, Asians) suffer during pregnancy. Because this disease does not cause symptoms, having this test is the only way to know if you have it.
Like any diagnostic test, the glucose screening test will not give you an accurate diagnosis but rather is aimed at identifying as many women as possible who may have a problem and need more tests to determine it.
If you tested positive on the initial test, you will have to go through a longer, more accurate test called the glucose curve or glucose tolerance test (GTT). Through this, you will be able to tell if you have pregnancy diabetes.
You may be tested before 24 weeks if one of your routine urine tests shows that there is a high amount of sugar in your blood, or if you suspect a high risk of gestational diabetes. If the results are normal, a test will be done again between the 24th and 28th week of pregnancy.
Obviously, if you’ve already been diagnosed with diabetes before pregnancy, you won’t need to be tested. Instead, to control this disease during your pregnancy, fasting glycaemia and control of glycosylated hemoglobin will be done, to know that the situation is compensated.
If the reading is not normal (it is too high), something that happens between 15 and 23 percent of the time, they will be ordered to perform a test that lasts three hours and is known as the glucose curve, to see if we really are dealing with diabetes of pregnancy.
Fortunately, the majority of women who test positive on the first test do not have pregnancy diabetes, in the world 1 in 7 (14%) of women have gestational diabetes and in Spain, approximately 9 in 100 pregnant women.
If the diagnosis is confirmed, it is advisable to follow the pregnancy together with an endocrinologist, in order to have an adequate diet, the weight gain wil be not excessive, if possible only 1kg per month, there are no peaks of hyperglycaemia and in the worst case ketosis, which would endanger the proper evolution of the pregnancy.