Gestational diabetes

This is a diagnosis that almost always arrives out of the blue: a woman feels perfectly well, has no complaints at all, and then a test result tells her she has diabetes of pregnancy. The first reaction is usually the same — alarm, and a sense of guilt about everything she has eaten. Both feelings are misplaced. Gestational diabetes is not the price of a sweet tooth; it is the result of what the hormones of the placenta do to the body's chemistry. It responds well to management, in most women it disappears as soon as the baby is born, and nearly all the risks described below are switched off by one thing: keeping blood sugar in range. There is work involved, but it is work that pays off, which cannot be said of every diagnosis.

Why blood sugar rises in pregnancy

From the second half of pregnancy onwards the placenta makes ever more of the hormones a growing baby needs, and those same hormones get in the way of insulin. Cells become less responsive to it, so to hold blood sugar where it was, the pancreas has to release far more insulin than usual. A pancreas with spare capacity manages this. If its margin is narrow, it falls behind, and blood sugar starts to climb.

That explains the shape of the illness. It almost never begins in the early weeks: the usual timing is the second and third trimesters, when the hormonal load is greatest. It generally causes no symptoms, because the rise is a moderate one. And it usually settles soon after birth, when the placenta that created the whole situation leaves the body.

One situation deserves separate attention: high blood sugar found early, in the first trimester. As a rule that is not gestational diabetes but type 2 diabetes that was already there before the pregnancy and had simply never been looked for. It is managed differently, with tighter control from the start, checks of the eyes and kidneys, and an awareness that high sugar in the first weeks affects how the baby's organs form. An early finding must therefore not be filed away as "just pregnancy diabetes, it will pass".

Who is at higher risk, and how it is diagnosed

It can happen to any woman, but the odds are higher if:

• there is excess weight, particularly with a body mass index of 30 or above;
• gestational diabetes occurred in a previous pregnancy;
• a previous baby was large, around four and a half kilograms or more;
• a parent, brother or sister has diabetes;
• there is polycystic ovary syndrome;
• you are older: risk climbs with age, and the exact threshold at which screening starts differs from country to country;
• your family background is South Asian, African, Caribbean or Middle Eastern, groups in which the risk is higher at the same weight;
• there has been an unexplained stillbirth or a very large baby in the past.

The diagnosis is made with a glucose test. In the morning, after a night without food, blood is taken, a glucose drink is given, and blood is taken again, usually after two hours and sometimes after one as well. The whole thing takes a couple of hours, during which you have to sit quietly: a walk down the corridor changes the result. Water is allowed. The test is done mainly between the twenty-fourth and twenty-eighth weeks, and if there was gestational diabetes before, as soon as antenatal care begins and then again later.

Two cautions. First, both the approach to screening and the cut-off values themselves differ between countries, so comparing your numbers with someone else's report or with figures found online tells you nothing; go by what your own doctor says. Second, women who have had stomach reduction surgery usually cannot take the sugary drink, which provokes a severe reaction; in them the diagnosis is made another way, normally by measuring blood sugar over several days.

What it means for mother and baby

Surplus sugar crosses the placenta freely; the mother's insulin does not. The baby is obliged to make its own insulin in excess, and insulin is a growth hormone. Almost every consequence follows from that.

• The baby grows larger than it should, putting the weight mainly on the shoulders and abdomen. That complicates delivery and raises the chance of birth injury, of induction and of caesarean section.
• The amount of amniotic fluid rises above normal, which brings a risk of premature labour and of problems during birth.
• The likelihood of pre-eclampsia increases: a condition with high blood pressure that is dangerous for mother and baby alike.
• After birth the baby's blood sugar can fall sharply, because it is producing plenty of insulin while the supply of glucose from the mother has stopped. Jaundice and breathing difficulties are also possible.
• Stillbirth is commoner when blood sugar is poorly controlled than when it is normal. It is rare, and preventing it is precisely what all the work of control is for.

The second half of that thought matters just as much: these are the risks of high blood sugar, not the risks of the diagnosis. When the numbers stay within target, most women have a pregnancy like anyone else's and a healthy baby at the end of it.

Food and movement: what works for most women

Treatment does not start with tablets. In roughly two women out of three, changing what is eaten and adding some activity is enough, and doctors allow a week or two to test that, going by the record of readings.

What makes sense with food:

• eat regularly, three main meals plus small snacks, and do not skip breakfast: after a long fast the sugar rise is steeper;
• choose slow carbohydrates: wholemeal bread, whole grains, durum wheat pasta, pulses, lentils, plain porridge oats;
• fill the plate with vegetables and add protein — fish, eggs, cottage cheese, poultry, pulses: with protein and fibre alongside, carbohydrate is absorbed more slowly;
• cut out sugary drinks, including juices and smoothies: liquid sugar raises the level faster than anything else;
• swap sweets for fruit, nuts or plain yoghurt, while remembering that fruit is carbohydrate too and half a kilo in one go still counts.

What not to do: go on a starvation diet and try to lose weight. Pregnancy is not the time for a deficit; the task is not to shed kilos but to spread carbohydrate through the day. A completely sugar-free diet is not required either.

Movement works as well as food does, and it works quickly. The single most effective trick is a fifteen or twenty minute walk after each meal: muscle takes glucose out of the blood without any insulin at all, and the post-meal peak comes out markedly lower. Overall the aim is about two and a half hours of moderate activity a week — walking, swimming, water aerobics, pregnancy yoga. Any form of exercise that is new to you should be checked first, and where there is a threat of premature labour or certain other conditions the plan is decided separately.

Self-monitoring and medication

You will be given a meter and shown how to use it. The usual pattern is to test on waking before breakfast and an hour after each meal, and to write the results down: it is from that record that the doctor judges whether diet alone is holding the line or medication is due. Readings are given in mmol/L; your target range will be set by your own doctor, it depends on the guidance in use where you live, and it is not something to pick off the internet.

The record is not only for the doctor. Within two or three weeks you will start to see for yourself which particular cereal or which snack sends the numbers up and which passes without a trace, and eating stops being a list of prohibitions.

If diet and activity have not been enough, or if the sugar was high from the outset, medication is added. This is usually metformin tablets or insulin; other glucose-lowering tablets are sometimes used. Being prescribed something does not mean you tried too little: as the pregnancy advances the hormonal load grows, and very often that is the whole explanation.

Insulin is worth understanding in advance, because it is feared out of all proportion. It is given with a pen, the needles are very fine and short, and the injection is barely felt. The dose usually has to be increased as the weeks pass, which is the normal course of events rather than a deterioration. Insulin does not cross to the baby and creates no dependence. After the birth it is stopped in the overwhelming majority of cases.

Insulin has a flip side: blood sugar can fall too low. The signs are shakiness, sweating, sudden hunger, pallor, a pounding heart, irritability and difficulty concentrating. When they appear, take something sugary at once, check the reading a quarter of an hour later, and follow it with slower carbohydrate. Carry something sweet with you at all times, particularly when driving, and do not skip meals. If you are on insulin and the readings swing unpredictably, ask about a continuous glucose sensor, which displays the level all the time.

Monitoring, timing and the birth

A pregnancy of this kind is watched more closely than usual. Added to the standard checks are scans in the third trimester to follow the baby's growth and the volume of amniotic fluid and, towards the end, frequent checks of blood pressure and of protein in the urine.

On timing there is one general rule: going far past the due date is not advised with gestational diabetes. If labour has not started on its own by the end of the fortieth week, induction is usually offered, and a caesarean where there is reason for one. An earlier birth is discussed if the baby is large, if the sugar is poorly controlled, or if other worrying signs appear. The diagnosis by itself does not mean a caesarean: most women give birth vaginally.

It is better to deliver where newborn care is available, since the baby may need watching for low blood sugar. Take your meter and your medication to hospital with you. Testing continues until labour begins, and during labour the level is monitored and insulin given by drip if it is needed.

Straight after the birth it matters to put the baby to the breast as early as possible, within the first half hour, and then to feed every two or three hours until its sugar is steady. The baby's glucose is checked in the first hours; if it is low, extra feeds help, and occasionally a drip is needed. Your own medication is normally stopped immediately after delivery, though your sugar goes on being measured for a day or two.

When to make contact rather than wait for the next appointment

Most of a pregnancy with gestational diabetes runs to plan. But some situations call for contacting your doctor or the maternity unit the same day rather than waiting.

• The baby is moving less, or differently from usual. This is the most important item on the list and it has nothing to do with diabetes: it needs checking straight away, not "tomorrow, if things don't pick up".
• Severe headache, spots or blurring in your vision, pain in the pit of the stomach or under the right ribs, sudden swelling of the face and hands, vomiting in the second half of pregnancy — this is how pre-eclampsia announces itself.
• Blood sugar staying high over several readings in a row despite following everything you have been told.
• Nausea and vomiting, abdominal pain, unusual drowsiness, deep rapid breathing or sweet-smelling breath, together with high readings. These point to ketoacidosis, which is rare in diabetes of pregnancy but dangerous and treated in hospital.
• Fever, stinging on passing urine or other signs of infection: with raised blood sugar infections run a harder course and themselves push the sugar higher.
• Leaking fluid, bleeding, or cramping pains before term.

An ambulance is called if blood sugar drops so low that the person loses consciousness, behaves strangely or has a seizure, and likewise if a pregnant woman with high blood pressure has a seizure. Across Europe the single emergency number is 112. Everything else on the list is not an ambulance matter but a reason to be seen that day.

After the birth, and afterwards

In most women blood sugar returns to normal within days and no more medication is needed. But the story does not end there, and that part often goes unsaid.

Between roughly six weeks and three months after the birth, a blood test for diabetes is needed: in a proportion of women the sugar stays high, and at that point it is no longer gestational diabetes but diabetes proper. If the result is normal, a check about once a year is sensible, because your chance of developing type 2 diabetes in the years ahead is higher than in women without this history. Come sooner if thirst, frequent urination, a dry mouth, unexplained tiredness or weight loss appear. And have the check even if you feel completely well: type 2 diabetes goes years without symptoms.

The encouraging part is that this risk really can be influenced. What works is the dullest advice there is: keeping weight steady, moving regularly, eating slow carbohydrates. Breastfeeding also lowers the later risk of diabetes, both for you and for the baby, whose own chance of excess weight and metabolic problems in later life is somewhat above average.

And about the next pregnancy. Gestational diabetes often comes back, so it is better planned than stumbled into: check your blood sugar before conceiving, start folic acid, and come to the pregnancy at a healthy weight if you can. Tell whoever will look after the pregnancy about the previous episode straight away — the glucose test will be arranged much earlier than the standard date.

Online consultation

A remote appointment covers well the things it is awkward to travel for but which raise a great many questions. The doctor will go through your record of readings and explain which foods and which times of day send your particular numbers up, help you rebuild the menu around the food you actually eat rather than someone else's list, and suggest how to fit the after-meal walk into a real day. They will explain why medication became necessary and what to expect from it, and show you what to do when the sugar drops. Preparing for the birth and what follows it is a subject in itself: the test a few months later, feeding, planning the next pregnancy. The warning signs listed above are not assessed through a screen: those need to be seen in person the same day.

This material is for information only and does not replace medical advice.