Gestational diabetes: what to eat, how to spread carbohydrates and what to expect after birth

What is gestational diabetes, and why does it occur?

Gestational diabetes is a rise in blood glucose first detected during pregnancy in a woman who did not have diabetes before. See “Pregnancy cravings”.

The placenta produces hormones that make insulin work less effectively. This is a change associated with pregnancy, and the mother’s pancreas responds by producing more insulin. When it cannot compensate enough, blood glucose rises.

You did not cause it by what you ate before you knew. Risk is higher with age, higher pre-pregnancy weight, a family history of diabetes or gestational diabetes in a previous pregnancy [1]. It can also occur in women with none of these factors, which is why everyone is screened.

In most cases, blood glucose returns to normal after birth [2]. Gestational diabetes also indicates a higher risk of diabetes in the future.

How is it diagnosed in Spain?

Spain follows a two-step strategy proposed by the Spanish Diabetes and Pregnancy Group [1]. The first step is the O’Sullivan test: you drink a liquid containing 50 g of glucose, and a blood sample is taken one hour later [1].

It is offered to all pregnant women between weeks 24 and 28 [1]. If you have a higher risk, for example because of your age, weight or previous gestational diabetes, it is also done in the first trimester [1].

If the O’Sullivan test result is abnormal, it is confirmed with a 100 g oral glucose tolerance test, with several blood samples taken over three hours [1]. The diagnosis is established with this second test and given to you by your obstetric team.

If you are at the beginning of your pregnancy, the basics for these weeks are in the first-trimester pregnancy nutrition guide.

What should you eat with gestational diabetes?

A gestational diabetes diet is very similar to a healthy diet during pregnancy. The difference is how carbohydrates are spread throughout the day. You can find the general foundations in the pregnancy diet guide.

Carbohydrates are not eliminated. Guidelines agree on a minimum of about 175 g of carbohydrate a day, 71 g of protein and 28 g of fibre [1] [2]. Avoiding bread, rice or fruit out of fear may mean that you and your baby do not get enough energy.

Carbohydrates stay on the plate. What changes is how much, when and what you eat them with.

What does change is how they are distributed:

• Space meals and snacks according to your plan. Have breakfast if it suits you and fits your routine; eating it matters more than the time. Add a mid-morning snack, afternoon snack or something before bed if this is part of your plan.
• Have fewer carbohydrates at breakfast than at other meals, because this is often the meal that is hardest to adjust.
• Include protein at every meal or snack, such as eggs, plain yoghurt, fresh cheese, pulses, fish, lean meat or nuts.
• Include fibre in almost every meal, through vegetables, pulses, whole fruit and whole grains.

Good staple carbohydrates include pulses, wholemeal bread and pasta, rice, potatoes, oats and whole fruit. They reach the bloodstream more slowly than sugar, especially when eaten with vegetables, olive oil and protein.

If you eat a vegetarian or vegan diet, the plan can be built in the same way with pulses, soya, nuts and dairy products or soya drink. Our team of dietitians specialising in vegetarian and vegan nutrition can adapt it with you.

What a day of meals might look like

This is a general example to show how meals can be distributed. Amounts depend on your weight, activity and blood glucose levels.

• Breakfast. A small slice of wholemeal toast with tomato and oil, scrambled egg and a glass of milk.
• Mid-morning snack. Plain yoghurt with a handful of walnuts.
• Lunch. Lentil stew with vegetables, a salad and a piece of fruit.
• Afternoon snack. A piece of fruit with a piece of fresh cheese.
• Dinner. Oven-baked hake with potatoes and green beans, and wholemeal bread if your blood glucose levels allow it.
• Before bed. A glass of milk or plain yoghurt, if this is part of your plan.

Each meal or snack includes some protein, fruit is eaten whole and the amount of bread is adjusted to your plan. With that in mind, you can swap in dishes you enjoy.

What should you avoid without banning anything?

Fast-acting sugars raise blood glucose the most, especially when eaten alone or in drinks. Juice is the one that surprises people most. Even when it is freshly squeezed, juicing removes the fibre and the sugar arrives all at once.

Products labelled ‘sugar-free’ or ‘for people with diabetes’ do not solve this either. They often contain refined flour, which also counts as carbohydrate, and they cost more.

If you feel like something sweet one day, have a small amount and see what your glucose meter shows afterwards. That reading will tell you more than any list.

Pregnancy food safety precautions remain the same. You can find them in what not to eat during pregnancy. Wash fruit and vegetables well, and avoid raw or undercooked meat if you do not know for certain whether you are immune to toxoplasmosis. When cooking meat, fish or eggs, make sure the centre reaches 70 °C (AESAN). There is no safe amount of alcohol for health (WHO): the less, the better. Do not drink any during pregnancy or breastfeeding, in childhood, if you are going to drive, or if your medication does not allow it.

What exercise can you do?

Being active helps because working muscles use glucose. Walking, swimming, using a stationary bike, or yoga and Pilates adapted for pregnancy are all suitable options.

Avoid sports with a risk of falling or being hit in the abdomen. Stop if you feel dizzy or have pain or bleeding. Before starting anything new, discuss it with your midwife or gynaecologist.

How is blood glucose monitored, and when is insulin needed?

After diagnosis, you will be shown how to check your blood glucose at home with a finger prick. The Spanish guideline proposes four blood glucose checks a day, before and after breakfast and before and after lunch or dinner, on alternate days [1].

The target levels used in the guidelines are below 95 mg/dl when fasting. After eating, they are below 140 mg/dl at one hour or below 120 mg/dl at two hours [1] [2]. Your team may set different targets for you.

If diet and exercise do not bring you to these targets within one or two weeks, treatment is added [1]. The medicine of choice is insulin [2]. This decision is made by your obstetric and endocrinology team, never by a dietary plan.

Needing insulin does not mean you have done anything wrong. Insulin resistance usually increases as pregnancy progresses, and sometimes food changes are not enough. With insulin, diet remains the foundation. If your blood glucose falls below 70 mg/dl, take 15-20 g of glucose and check it again after 15 minutes (ADA).

What happens after giving birth?

Most women no longer need treatment after giving birth [2]. However, there is one important point to remember. The risk of developing type 2 diabetes later is almost ten times higher than for someone who did not have gestational diabetes [3].

That is why follow-up is needed. A 75 g oral glucose tolerance test is done between 4 and 12 weeks after birth [2]. The Spanish guideline prefers it between weeks 6 and 12 [1]. After that, blood glucose is checked every one to three years for life [2].

Breastfeeding is also recommended for this reason, as it is associated with a lower risk of developing type 2 diabetes later [2]. While breastfeeding, return to your usual weight gradually and without restrictive diets. The safest option is not to drink alcohol while breastfeeding.

What you have learned over these months can help you afterwards. Eating regular meals with vegetables, pulses and whole grains, and being active every day, provide the same foundation for looking after your blood glucose in the long term.

What mistakes do we see in consultations?

• Cutting out almost all carbohydrates. Blood glucose falls, but you are left without enough energy and far below the minimum you need.
• Skipping a planned meal or snack. You may be very hungry by the next meal.
• Switching to juice labelled ‘no added sugar’. It is still juice.
• Checking your blood glucose only on days when you eat well. Checks are more useful on ordinary days.

And the question that almost always comes up at the first appointment: whether what you ate before diagnosis affected the baby. What you do from today onwards is what counts, and your medical team monitors the baby’s growth at each check-up.