O’Sullivan’s Test: What Does it Consist Of?

Pregnant women must undergo many tests to ensure that everything is progressing well. Find out all about this particular test, what it consists of, and how useful it is. Keep reading!

Women are subject to certain diseases during pregnancy. Therefore, it’s important to periodically study maternal health status through various tests. One of the tests that must be performed is O’Sullivan’s test, useful for the diagnosis of gestational diabetes.

Gestational diabetes is a carbohydrate intolerance that’s diagnosed for the first time during pregnancy, and its intensity can vary. This is a common problem worldwide and it’s estimated that between 2 and 9% of all pregnant women have it.

This pregnancy complication exposes the fetus to large amounts of glucose, which can cause it to be over or under size. In addition, it creates health problems for the mother, such as hypertension, which can lead to other complications.

What’s O’Sullivan’s test?

The O'Sullivan test requires a sample.
This study requires a blood sample.

In simple words, O’Sullivan’s test consists of measuring blood glucose values after an oral intake of 50 grams of this type of sugar. Plasma levels must be evaluated 1 hour after ingestion, so that the body can process the sugars consumed.

The test doesn’t require much preparation before carrying it out, and it can be done at any time of the day and without taking into account the previous food intake. Patients shouldn’t follow a strict diet in the days before the test; in fact, it’s best for them to continue with their normal daily life.

As mentioned earlier, one of the main uses of this test is to determine the risk of developing gestational diabetes. The O’Sullivan test can be performed from the 14th week of gestation, however, the ideal thing is to perform it during the 24th and 28th week, where it reaches a sensitivity of 80%.

The early diagnosis of gestational diabetes is of vital importance, as the presence of this condition increases the likelihood of suffering maternal and fetal complications. In this way, it’s possible to take corrective measures in time and avoid permanent damage.

Who should take this test?

It’s very important for all pregnant women to take this test to ensure that their blood glucose levels are within the normal range. However, the O’Sullivan test is of greater importance in women with a moderate or high risk of complications from pregnancy.

Women at moderate risk of gestational diabetes are all those over 25 years of age who don’t have any other risk factors. In these cases, the ideal thing is to perform the test in question only in the 24th week of pregnancy. If the results are satisfactory, the test shouldn’t be repeated, unless the specialist deems it necessary.

On the other hand, there’s a high risk of gestational diabetes when you’re over 25 and have at least one of the following risk factors:

  • Obesity with a body mass index of greater than 30
  • The presence of glucose in the urine
  • A personal or family history of gestational diabetes
  • Some obstetric pathology

Several studies state that these women must undergo the corresponding examination in the 24th week of pregnancy. In addition, it should be repeated between the 32nd and 36th weeks to have better control over the evolution of the pregnancy.

What is the procedure?

The O'Sullivan test and its performance.
This test is different from simply measuring your sugar with a glucometer.

The test in question isn’t much different from a conventional blood test. In fact, you can carry it out at any time of the day and you mustn’t fast. Firstly, the specialist will draw a blood sample to establish baseline glucose values.

After completing the first step, you should drink a glass of very sweet juice with 50 grams of glucose. Then, you’ll have to sit down without eating or drinking anything, for at least an hour, until the specialist takes a new blood sample to analyze blood glucose and compare it with baseline levels.

After the second extraction, the test will end and you’ll be free to return to your daily activities. The O’Sullivan test generally has no immediate side effects, except pain where the needle was inserted.

Analysis of the results

Blood plasma glucose levels should be less than 140 milligrams per deciliter 1 hour after glucose administration. In this sense, when a patient has higher values, O’Sullivan’s test is considered positive, however, this isn’t enough to make a diagnosis.

This test can have false positives, so whenever you have a positive result, you’ll need to subject the patient to an oral glucose tolerance test. This test is very similar, the difference being that the amount of glucose ingested will be greater, and, in addition, the measurements will be made after 2 and 3 hours.

A baseline blood glucose level greater than 125 milligrams per deciliter or a blood glucose level greater than 200 milligrams per deciliter at any time of the day will be sufficient criteria to confirm the diagnosis of gestational diabetes.

A fundamental test that should always be carried out

The O’Sullivan test is one of the most important tests in the second trimester of pregnancy, especially in women at risk of gestational diabetes. Early diagnosis is essential in order to avoid possible complications during pregnancy and at delivery.

Women with a positive result will need to make dietary changes and decrease their carbohydrate intake. In addition, a constant medical check-up is vitally important in order to detect any possible complications in time and avoid serious damage.

  • Rojas-Carrera S, Márquez-Celedonio F, Lagunes-Mijangos A, González-Arriola V. Precisión diagnóstica de la prueba de O’Sullivan en diabetes gestacional. Rev Med Inst Mex Seguro Soc. 2013;51(3):336-9.
  • Plana Pintos R, Vázquez Troitiño F, Pérez Vences J, Malo García F et al. Diabetes Gestacional. Cad. Aten. Primaria. 2005; 12: 163-165.
  • Mañé Serra L. Un O’Sullivan alterado: caso clínico. Diabetes Práctica 2017;08(04):145-192.
  • Abenza Campuzano J. Cribado de diabetes gestacional con test de O’Sullivan. AMF 2015;11(2):103-105.
  • Codina M, Corcoy R, Goya M, Acosta Delgado D, Ballesteros Pérez M, Bandres Nivela M et al. Actualización urgente: alternativa temporal para el diagnóstico de hiper-glucemia gestacional y el seguimiento de estas mujeres y aquellas con diabetes pregestacional durante la pandemia COVID-19. Endocrinología, Diabetes y Nutrición. 2020;67(8):545-552.
  • Medina-Pérez E, Sanchez-Reyes A, Hernández-Penedo A, Martínez-López M et al. Diabetes gestacional. Diagnóstico y tratamiento en el primer nivel de atención. Med Int Méx. 2017 ene;33(1):91-98.