Gestational diabetes risk factor checker

Two different questions that keep getting merged

"Do I have gestational diabetes?" is answered by a blood test. "Will I be offered that blood test?" is answered, in the UK, by a conversation at your booking appointment in which nobody takes any blood at all.

That second question is what this tool is for, and it catches people out because the answer feels arbitrary. A friend gets sent for the test and you do not. Someone in an antenatal group mentions hers was at 16 weeks and yours is at 27. None of this is random; it is a short published rule.

The five things a midwife is checking

NICE NG3 lists five risk factors, assessed at booking. A BMI of 30 or over. A previous baby weighing 4.5 kg or more. Gestational diabetes in a previous pregnancy. A first-degree relative — parent, brother or sister — with diabetes. And an ethnicity with a high prevalence of diabetes.

Any one of them means being offered a 75 gram, two-hour glucose tolerance test at 24 to 28 weeks. They are not scored or added. One is the same as three, as far as the decision goes.

The 4.5 kilogram threshold is worth looking up rather than remembering

Family stories round birth weights, and 4.5 kg is 9 lb 15 oz — which plenty of people describe as "about ten pounds". A 4.3 kg baby is a big baby and is not on NICE's list. If you are answering this from memory, the red book or the birth notes will settle it.

The first-degree relative rule is similarly precise. A grandparent, aunt or uncle with type 2 diabetes does not meet it, however much it feels like it should.

Why previous gestational diabetes is treated differently

Recurrence is common enough that waiting until 24 weeks would waste months. So NICE offers women who have had it before either early self-monitoring at home, or a glucose tolerance test as soon as possible after booking — plus a repeat at 24 to 28 weeks if the first is normal.

That choice is real and it is yours. Some women much prefer several weeks of finger-pricks to another morning of fasting and a sweet drink; others would rather have one test and be done. Say which you would prefer rather than waiting to be assigned one.

The route in that has nothing to do with risk factors

Every antenatal appointment includes a urine dipstick, and glucose can show up on it. NICE says to consider further testing where there is glycosuria of 2+ or above once, or 1+ or above on two or more occasions.

A single 1+ does not meet the threshold, which is worth knowing if you have been sent home with a vague comment about sugar in your urine. It is worth having recorded, because if it happens again it counts.

The test you already had does not count

This is the most useful negative in the whole guideline. NICE recommendation 1.2.3 says do not use fasting plasma glucose, random blood glucose, HbA1c, a glucose challenge test or urinalysis to assess the risk of gestational diabetes.

So a normal HbA1c at booking does not replace the OGTT. Neither does a normal finger-prick at a well-woman check, nor a home glucose meter your partner uses. The two-hour test exists because gestational diabetes is specifically about how you handle a glucose load in the second half of pregnancy, when placental hormones are actively making you insulin-resistant. A snapshot taken earlier, or without a load, measures something else.

What the risk factors are actually pointing at

None of the five is a cause. Gestational diabetes happens because the placenta produces hormones — human placental lactogen chief among them — that make you resistant to your own insulin. In most pregnancies the pancreas compensates by producing more. Gestational diabetes is what happens when it cannot keep up.

So the risk factors are all proxies for how much reserve your pancreas has, or how much insulin resistance you started with. A higher BMI increases baseline insulin resistance. A family history points at inherited beta-cell function. A previous large baby is a retrospective clue that glucose may have been running high last time, diagnosed or not. And previous gestational diabetes is the strongest signal of all, because it is direct evidence of how your pancreas behaved under exactly this load.

That framing matters because women routinely arrive at a diagnosis convinced it was caused by what they ate. It was not. Diet is a lever for managing it; it is not why it happened.

Why the UK tests fewer women than most countries

Britain screens by risk factor. Much of Europe, Australia and a large part of the United States screen universally — every pregnant woman gets a test, regardless of history.

Both approaches are defensible and both have costs. Risk-based screening misses some women, because a proportion of gestational diabetes occurs in women with no risk factors at all. Universal screening finds those women, and also diagnoses a much larger number with mild hyperglycaemia whose pregnancies would have been fine, with all the monitoring and anxiety that brings.

If you are reading American or Australian advice and wondering why nobody has offered you a test, this is why. It is not an oversight.

What a "no test offered" result actually means

It means you do not meet the criteria for routine screening today. It does not close the door. Glucose in a urine sample, a baby measuring large on a growth scan, or excess amniotic fluid can all bring testing back into the picture later in the pregnancy, and your midwife reassesses as things change.

This tool applies a published rule to your answers. It does not diagnose anything, and it does not replace the risk assessment your midwife carries out at the booking appointment.