A raised result on the one hour glucose test during pregnancy can feel alarming, but it is important to understand what it does — and does not — mean. The one hour glucose test (also called the glucose challenge test) is a screening tool used between 24 and 28 weeks of pregnancy to identify women who may be at risk of gestational diabetes. A raised result is not a diagnosis; it is a prompt for further investigation, typically a two hour oral glucose tolerance test (OGTT). This article explains what a raised result means, why it occurs, what happens next, and when to contact your midwife or GP.

What a Raised Result on the One Hour Glucose Test Means

A raised one hour glucose test result (above 7.8 mmol/L) indicates a positive screen for gestational diabetes risk, not a confirmed diagnosis; a follow-up OGTT is required to confirm or exclude the condition.

The one hour glucose test — sometimes called the glucose challenge test (GCT) — is a screening tool used during pregnancy, typically between 24 and 28 weeks of gestation, to identify women who may be at risk of gestational diabetes mellitus (GDM). It is important to note that this particular test format is more commonly used in the United States and some private healthcare settings in the UK; within the NHS, a two hour oral glucose tolerance test (OGTT) is the standard diagnostic approach (NICE NG3).

During the one hour test, you drink a solution containing 50 grams of glucose and have a blood sample taken one hour later. A result above the threshold — commonly set at 7.8 mmol/L in many protocols, though this varies by provider and is not a fixed NHS standard — is considered a raised or positive screen. A raised result does not confirm a diagnosis of gestational diabetes. Rather, it indicates that further investigation is needed.

Many women feel anxious upon hearing they have a raised result, but it is reassuring to know that a significant proportion of those who screen positive will not go on to be diagnosed with gestational diabetes following confirmatory testing. The one hour test is intentionally sensitive, meaning it casts a wide net to avoid missing genuine cases. Receiving a raised result is therefore a prompt for further evaluation, not a definitive diagnosis, and should be discussed calmly with your midwife or obstetric team.

References: NICE NG3 (Diabetes in pregnancy); NHS UK – Gestational diabetes.

Why Results Can Be Raised and Common Causes

Results can be raised due to normal pregnancy insulin resistance, recent food intake, acute illness, or established risk factors such as high BMI, previous gestational diabetes, or relevant family history.

There are several reasons why blood glucose may be elevated one hour after consuming the glucose drink, and not all of them indicate an underlying problem with glucose metabolism. Understanding these factors can help contextualise your result.

Physiological factors that may contribute to a raised result include:

• Normal pregnancy physiology: Pregnancy naturally induces a degree of insulin resistance, particularly in the second and third trimesters, driven by placental hormones such as human placental lactogen, oestrogen, and cortisol. This is a normal adaptation but can push glucose levels higher than usual.

• Recent food intake: If you ate shortly before the test (some protocols do not require fasting), this can artificially elevate your result. Always follow the preparation instructions provided by your maternity team.

• Acute illness or infection: Physiological stress raises cortisol and adrenaline, both of which can transiently increase blood glucose levels. If you are acutely unwell on the day of your test, contact your maternity team to discuss whether it should be rescheduled.

Risk factors associated with a raised result and an increased likelihood of gestational diabetes include:

• Body mass index (BMI) above 30 kg/m²

• A previous pregnancy affected by gestational diabetes

• A family history of type 2 diabetes (first-degree relative)

• South Asian, Black African, African-Caribbean, or Middle Eastern ethnic background

• A previous baby weighing 4.5 kg or more at birth

• Glycosuria detected on urine dipstick (2+ on one occasion, or 1+ on two or more occasions) — a common trigger for OGTT referral in UK practice

Certain medications, such as corticosteroids, can also transiently raise blood glucose. If you are taking any regular medication, inform your healthcare team, as this may be relevant to interpreting your result.

References: NICE NG3 (risk factors and indications for testing); NHS UK – Gestational diabetes (who is offered testing).

Next Steps: The Two Hour Oral Glucose Tolerance Test

The confirmatory next step is a two hour OGTT after an overnight fast, using NICE NG3 thresholds of 5.6 mmol/L fasting and 7.8 mmol/L at two hours to diagnose or exclude gestational diabetes.

Following a raised one hour glucose screen, the standard next step is a two hour oral glucose tolerance test (OGTT). This is the confirmatory diagnostic test recommended by NICE and used routinely across NHS maternity services. Unlike the one hour screen, the OGTT requires an overnight fast of at least eight hours before the test.

During the OGTT, a fasting blood sample is taken first, followed by consumption of a 75-gram glucose solution. A second blood sample is then taken two hours after the drink. These two measurements — the fasting baseline and the two hour response — provide the information needed to make or exclude a diagnosis of gestational diabetes. Some units may take an additional sample at one hour for local audit or research purposes, but under NICE guidance, the diagnosis is based on the fasting and two hour values only.

NICE diagnostic thresholds for gestational diabetes (OGTT):

• Fasting plasma glucose: 5.6 mmol/L or above

• Two hour plasma glucose: 7.8 mmol/L or above

A diagnosis of gestational diabetes is made if either threshold is met or exceeded. If both values fall below these thresholds, gestational diabetes is not confirmed, and you can be reassured accordingly.

The OGTT is generally well tolerated, though some women experience mild nausea after drinking the glucose solution. You will be asked to remain at the clinic or hospital for the duration of the test, which typically takes around two to two and a half hours in total. Bring something to read or listen to, and avoid strenuous activity during the waiting period, as this can affect results. If you are acutely unwell on the day, contact your maternity team before attending, as the test may need to be rescheduled.

References: NICE NG3 (diagnostic thresholds and OGTT protocol); NHS UK – Gestational diabetes (diagnosis).

Gestational Diabetes: Diagnosis and NHS Guidance

Gestational diabetes affects around 4–5% of UK pregnancies and is diagnosed using NICE NG3 criteria; with appropriate management, the majority of affected women have healthy pregnancies and babies.

Gestational diabetes mellitus (GDM) is defined as glucose intolerance that is first recognised during pregnancy. It affects around 4–5% of pregnancies in the UK overall, though rates vary by population and the diagnostic criteria used (NICE NG3; NHS UK). NICE guideline NG3 (Diabetes in Pregnancy) provides the framework for diagnosis and management within NHS maternity services.

GDM develops when the pancreas cannot produce sufficient insulin to overcome the increased insulin resistance of pregnancy. This leads to elevated circulating glucose levels, which cross the placenta and affect the developing baby. If left unmanaged, GDM is associated with a range of complications, including:

• For the baby: macrosomia (large birth weight), neonatal hypoglycaemia, preterm birth, and an increased risk of developing type 2 diabetes later in life

• For the mother: increased likelihood of caesarean section, pre-eclampsia, and a higher risk of developing type 2 diabetes after pregnancy

However, it is important to emphasise that with appropriate monitoring and management, the vast majority of women with gestational diabetes have healthy pregnancies and healthy babies. Early diagnosis through screening is precisely what enables timely intervention.

Following a confirmed diagnosis, you will typically be referred to a joint obstetric–diabetes clinic or a specialist midwife with expertise in diabetes in pregnancy. NICE and the NHS advise that women with GDM receive structured education about blood glucose monitoring, dietary modification, physical activity, and, where necessary, medication. Regular antenatal appointments will be more frequent to monitor both maternal and foetal wellbeing.

References: NICE NG3 (care pathway and education); NHS UK – Gestational diabetes (prevalence and overview).

Managing Blood Sugar Levels During Pregnancy

NICE recommends fasting glucose of 5.3 mmol/L or below and one hour post-meal glucose of 7.8 mmol/L or below; management begins with diet and exercise, escalating to metformin or insulin if targets are not met.

Effective management of blood glucose during pregnancy centres on maintaining levels within a safe target range to minimise risks to both mother and baby. NICE recommends the following target blood glucose levels for women with gestational diabetes:

• Fasting (before breakfast): 5.3 mmol/L or below

• One hour after meals: 7.8 mmol/L or below

Where a service uses two hour post-meal testing rather than one hour, NICE also specifies an alternative target of 6.4 mmol/L or below at two hours after meals. Your diabetes-in-pregnancy team will advise which targets apply to you.

Management is typically stepwise, beginning with lifestyle measures and escalating to medication if targets are not achieved.

Dietary modification is the cornerstone of initial management. A registered dietitian will usually provide personalised advice, which commonly includes:

• Reducing refined carbohydrates and sugary foods and drinks

• Choosing low glycaemic index (GI) carbohydrates (e.g., oats, lentils, wholegrain bread)

• Eating regular, balanced meals and avoiding large portions

• Increasing dietary fibre and non-starchy vegetables

Physical activity also plays an important role. Regular moderate exercise — such as walking, swimming, or pregnancy yoga — improves insulin sensitivity and can help lower blood glucose levels. Aim for at least 150 minutes of moderate activity per week, in line with NHS guidance, unless advised otherwise by your healthcare team.

If blood glucose targets are not met within one to two weeks of dietary and lifestyle changes, medication may be introduced. Metformin is often the first-line pharmacological option; it works by reducing hepatic glucose production and improving peripheral insulin sensitivity. Common side effects of metformin are gastrointestinal (such as nausea or loose stools), which often improve with time or dose adjustment. Metformin used alone does not commonly cause hypoglycaemia (low blood sugar). If metformin is insufficient or not tolerated, insulin therapy may be recommended. Insulin does not cross the placenta and is considered safe in pregnancy; hypoglycaemia is a recognised risk with insulin and will be discussed with you by your specialist team. All medication decisions will be made collaboratively with your specialist team, taking into account your individual circumstances.

If you experience any suspected side effects from your medication, you can report these to the MHRA via the Yellow Card Scheme at yellowcard.mhra.gov.uk.

References: NICE NG3 (glycaemic targets and pharmacotherapy); BNF – Metformin; BNF – Insulin (safety in pregnancy).

When to Speak to Your Midwife or GP

Contact your midwife or GP promptly if you have not been offered a follow-up OGTT, are struggling to meet glucose targets, or experience symptoms of high blood glucose; seek urgent help if on insulin and experiencing hypoglycaemia.

If you have received a raised result on a one hour glucose screen, the most important first step is to contact your midwife or obstetric team to arrange follow-up testing. Do not wait for your next routine appointment if you have not already been given a date for your OGTT — prompt investigation is important, particularly if you are already in the second or third trimester.

Contact your midwife, GP, or diabetes-in-pregnancy team promptly if you:

• Have not been offered a follow-up OGTT after a raised screening result

• Have been diagnosed with gestational diabetes and are struggling to meet blood glucose targets despite dietary changes

• Experience symptoms that may suggest very high blood glucose, such as excessive thirst, frequent urination beyond normal pregnancy levels, blurred vision, or unusual fatigue

• Have concerns about your baby's movements — always contact your maternity unit directly without delay if you notice reduced or changed fetal movements (NHS UK – Your baby's movements in pregnancy)

Seek urgent medical attention if you:

• Are on insulin therapy and experience symptoms of hypoglycaemia (low blood sugar) — these include shakiness, sweating, confusion, or feeling faint. For urgent advice, contact your maternity triage unit or call NHS 111; call 999 if someone is unconscious or having a seizure

• Have blood glucose readings consistently above target despite following your management plan — contact your diabetes-in-pregnancy team or maternity triage for guidance

Note that hypoglycaemia is primarily a risk with insulin therapy. Metformin used on its own does not commonly cause low blood sugar, though you should still follow your team's advice about monitoring.

After your baby is born, gestational diabetes usually resolves, but this is not always the case. NICE recommends that women who have had GDM are offered a fasting plasma glucose test at six to thirteen weeks postpartum to exclude persistent diabetes, and annual HbA1c testing thereafter, given the elevated lifetime risk of developing type 2 diabetes. Maintaining a healthy weight, staying physically active, and following a balanced diet after pregnancy are all evidence-based strategies to reduce this long-term risk.

References: NICE NG3 (postnatal testing recommendations); NHS UK – Your baby's movements in pregnancy; NHS 111.

Frequently Asked Questions