Glucose Load Test in Pregnancy: OGTT Guide
The glucose load test in pregnancy, more formally known as the oral glucose tolerance test (OGTT), is a routine NHS procedure used to screen for gestational diabetes mellitus (GDM). During pregnancy, placental hormones can reduce insulin sensitivity, and when the pancreas cannot compensate, blood glucose rises. Detecting this early matters, as unmanaged GDM is linked to complications for both mother and baby. This article explains who needs the test, how it is carried out, what the results mean, and how gestational diabetes is managed if diagnosed.
Summary: The glucose load test in pregnancy refers to the NHS oral glucose tolerance test (OGTT), a 75 g two-hour procedure used to diagnose gestational diabetes mellitus in women with identified risk factors.
- The OGTT involves a fasting blood sample, a 75 g glucose drink, and a second blood sample two hours later.
- NICE NG3 diagnoses gestational diabetes if fasting plasma glucose is 5.6 mmol/litre or above, or the two-hour reading is 7.8 mmol/litre or above.
- Testing is offered between 24 and 28 weeks; women with a previous GDM diagnosis are tested as early as possible after booking.
- Risk factors include BMI above 30, a previous large baby, family history of type 2 diabetes, and certain ethnic backgrounds.
- Management combines dietary changes, blood glucose monitoring, and medication (metformin or insulin) if lifestyle measures are insufficient.
- A postnatal fasting glucose test at 6 to 13 weeks is recommended, followed by annual HbA1c, as GDM raises lifetime risk of type 2 diabetes.
Table of Contents
What is the glucose load test and why is it done in pregnancy?
The glucose load test in pregnancy is the OGTT, offered by the NHS to women with risk factors to detect gestational diabetes, which arises when placental hormones impair insulin sensitivity and blood glucose rises.
The term "glucose load test" is sometimes used colloquially to describe the oral glucose tolerance test (OGTT), which is the standard NHS procedure for diagnosing gestational diabetes mellitus (GDM). The OGTT measures how efficiently the body processes a standard glucose drink, giving clinicians an indication of whether insulin response is functioning as expected.
During pregnancy, hormones produced by the placenta can reduce the body's sensitivity to insulin, a process sometimes called physiological insulin resistance. For most women, the pancreas compensates by producing more insulin. When it cannot keep pace, blood glucose rises and gestational diabetes develops. Left undetected and unmanaged, GDM is associated with complications including a larger-than-average baby (macrosomia), increased likelihood of caesarean delivery, and a higher risk of the baby developing low blood sugar after birth.
NICE guidance (NG3) recommends that women with one or more risk factors are offered testing for gestational diabetes.[1][3] Risk factors include:
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A BMI above 30 kg/m²
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A previous baby weighing 4.5 kg or more
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A previous diagnosis of gestational diabetes
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A first-degree relative with type 2 diabetes
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South Asian, Black African, African-Caribbean or Middle Eastern family origin
NICE also advises that significant glycosuria detected during routine antenatal urine testing should prompt consideration of an OGTT, even in the absence of other risk factors.[1][3]
Understanding why the test is offered helps women engage with the process and act promptly on results.
| Stage | Timing | Procedure | NICE NG3 Diagnostic Threshold | Next Steps if Threshold Met |
|---|---|---|---|---|
| Fasting preparation | 8 to 10 hours before appointment | Fast overnight, water only permitted | Not applicable | Attend clinic as instructed; inform team of any nausea |
| Fasting blood sample | On arrival at clinic | Venous blood draw to measure fasting plasma glucose | 5.6 mmol/litre or above confirms GDM | Proceed to glucose drink regardless of fasting result |
| Glucose drink | Immediately after fasting sample | Drink solution containing 75 g glucose | Not applicable | Remain at clinic; avoid food, non-water drinks and strenuous exercise |
| Two-hour blood sample | Two hours after glucose drink | Second venous blood draw to measure plasma glucose | 7.8 mmol/litre or above confirms GDM | Either value alone is sufficient for diagnosis |
| Results and referral | Within a few days of test | Communicated by midwife or GP | Either threshold met confirms GDM | Referral to joint obstetric and diabetes clinic within one week |
| Postnatal follow-up | 6 to 13 weeks after delivery | Fasting plasma glucose test to confirm GDM resolution | Not applicable | Annual HbA1c testing thereafter due to increased type 2 diabetes risk |
What do your results mean and what happens next?
Gestational diabetes is diagnosed if fasting plasma glucose is 5.6 mmol/litre or above, or the two-hour reading is 7.8 mmol/litre or above; a positive result triggers referral to a joint obstetric and diabetes clinic within one week.
The OGTT produces two readings: a fasting plasma glucose taken before the glucose drink, and a two-hour plasma glucose taken after it. According to NICE NG3, gestational diabetes is diagnosed if either the fasting plasma glucose is 5.6 mmol/litre or above, or the two-hour plasma glucose is 7.8 mmol/litre or above. Either value alone is sufficient to confirm the diagnosis; both do not need to be abnormal.
If your result is below both thresholds, no further glucose testing is usually required unless new risk factors or symptoms emerge, or you were tested early in pregnancy (for example, because of a previous diagnosis of GDM), in which case a repeat OGTT at 24 to 28 weeks may be recommended. Your midwife or GP will advise you accordingly.
If your result meets the diagnostic threshold for gestational diabetes, your maternity team will refer you promptly to a joint obstetric and diabetes clinic. NICE NG3 recommends that women are seen within one week of diagnosis. At that appointment, the team will discuss blood glucose monitoring, dietary changes, physical activity, and whether medication may be needed.
Understanding what the numbers mean can reduce anxiety and help women feel prepared for the next steps in their care.
Managing gestational diabetes after an abnormal result
Gestational diabetes is managed with dietary changes, blood glucose monitoring, and medication such as metformin or insulin if targets are not met; postnatal follow-up is essential due to the increased lifetime risk of type 2 diabetes.
Gestational diabetes is managed through a combination of lifestyle changes, blood glucose monitoring, and, where necessary, medication, with the goal of keeping blood glucose within safe target ranges throughout the remainder of pregnancy. NICE NG3 recommends that women with GDM aim for a fasting plasma glucose below 5.3 mmol/litre and a one-hour post-meal capillary plasma glucose below 7.8 mmol/litre. Where a one-hour reading is not practical, a two-hour post-meal target of 6.4 mmol/litre or below may be used instead. Individual targets may be adjusted by the clinical team.
Dietary changes are usually the first step. A registered dietitian will typically advise reducing refined carbohydrates, spreading carbohydrate intake across meals and snacks, and increasing fibre-rich foods. Regular moderate physical activity, such as walking after meals, can also help improve insulin sensitivity.
If blood glucose remains above target despite lifestyle measures, medication is considered. Metformin is often the first oral option offered. Its use in gestational diabetes is off-label in the UK, but it is recommended by NICE NG3 on the basis of established evidence and a good safety profile in pregnancy.[1][10] If metformin is insufficient or not tolerated, insulin therapy is introduced. Insulin does not cross the placenta and is considered safe for the baby.[7][9] The type and timing of insulin will be tailored to the individual's glucose pattern.
Women with gestational diabetes will have more frequent antenatal appointments and additional ultrasound scans to monitor fetal growth. After delivery, blood glucose usually returns to normal. NICE NG3 recommends a fasting plasma glucose test at six to thirteen weeks postnatally to confirm resolution of GDM, followed by annual HbA1c testing thereafter, because GDM significantly increases the lifetime risk of developing type 2 diabetes.[1][3] Breastfeeding is encouraged, as it supports both maternal and infant metabolic health.
How is the glucose load test carried out on the NHS?
The NHS OGTT is a 75 g two-hour test performed at a hospital or community clinic after an 8 to 10 hour fast, with blood samples taken before and two hours after drinking the glucose solution.
On the NHS, the standard test used to diagnose gestational diabetes is the oral glucose tolerance test (OGTT), a 75 g, two-hour procedure. It is typically carried out between 24 and 28 weeks of pregnancy. Women who have had gestational diabetes in a previous pregnancy are offered an OGTT as soon as possible after their booking appointment; if that result is normal, a repeat OGTT is offered at 24 to 28 weeks. The exact timing of early testing may vary between NHS trusts.
The test is performed at a hospital or community clinic and takes approximately two hours from start to finish. Women are asked to fast beforehand, usually for 8 to 10 hours, drinking only water.[4][6] Follow your clinic's specific instructions, as the fasting period may vary depending on your appointment time.
On arrival, a blood sample is taken to measure the fasting plasma glucose level. The woman then drinks a solution containing 75 g of glucose. A second blood sample is taken two hours later to assess how the body has processed the glucose load. During the waiting period, women are asked to remain at the clinic and avoid eating, drinking (other than water), or doing strenuous exercise.
The test is straightforward but can feel lengthy, so it is worth bringing something to read or listen to. Some women experience mild nausea after drinking the glucose solution, particularly if they are already experiencing morning sickness. Informing the clinic team beforehand allows them to offer practical support.
Results are usually available within a few days and communicated by the midwife or GP. Women who are unsure whether they need testing, or who have questions about their risk factors, should speak to their midwife at their booking appointment. Bolt Pharmacy is a GPhC-registered UK online pharmacy offering online consultations with prescriber review and pharmacist support for a range of conditions; gestational diabetes management should always be led by the NHS maternity team.
Scientific References
- Diabetes in pregnancy: management from preconception to the postnatal period (NG3) – Recommendations.
- Diabetes in pregnancy (NG3) – Your blood glucose levels during pregnancy.
- Diabetes in pregnancy: management from preconception to the postnatal period (NG3) – Guideline overview.
- Gestational diabetes.
- Gestational diabetes – Treatment.
- Diabetes | Treatment summaries – BNF/NICE.
- Transplacental Passage of Insulin in Pregnant Women with Insulin-Dependent Diabetes Mellitus.
- How the First 9 Months Shape the Rest of Your Life: The Impact of Gestational Diabetes on the Metabolic Future. Diabetes, Obesity & Metabolism..
- The care of pregestational and gestational diabetes and drug metabolism considerations. Expert Opinion on Drug Metabolism & Toxicology..
- The emerging role of metformin in gestational diabetes mellitus. Diabetes, Obesity & Metabolism..
- Metformin safety during pregnancy in women with gestational diabetes mellitus: A systematic review and meta-analysis of maternal, neonatal and long-term outcomes. Diabetic Medicine..
- Postpartum GLP-1 receptor agonists and SGLT-2 therapies in women with prior gestational diabetes: current evidence and uncertainties. BMC Medicine..
Frequently Asked Questions
Do I need to fast before the glucose load test in pregnancy?
Yes, you will be asked to fast for 8 to 10 hours before the OGTT, drinking only water. Follow your clinic's specific instructions, as the exact fasting period may vary slightly depending on your appointment time.
What happens if my glucose load test result is normal?
If both the fasting and two-hour readings fall below the diagnostic thresholds, no further glucose testing is usually needed unless new symptoms or risk factors arise. Women tested early due to a previous GDM diagnosis may be offered a repeat OGTT at 24 to 28 weeks.
Is metformin safe to use for gestational diabetes in the UK?
Metformin is used off-label for gestational diabetes in the UK but is recommended by NICE NG3 on the basis of established evidence and a good safety profile in pregnancy. If metformin is insufficient or not tolerated, insulin therapy, which does not cross the placenta, is introduced.
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