A review of the effect of dietary advice to prevent gestational diabetes was conducted by researchers in the Cochrane Collaboration. After searching for all relevant studies, they found two studies done by other researchers. Their findings are summarised below.
Please note that this Cochrane review has been updated since the summary below. See the abstract of that update here.
What is gestational diabetes and why dietary advice?
Diabetes is a condition in which your blood sugar (also called blood glucose) is too high. When this happens for the first time during pregnancy this is called gestational diabetes. Some women with gestational diabetes will have no symptoms. Others may feel tired or very thirsty; they may pass a lot of urine or have blurred vision.
Usually, gestational diabetes goes away after your baby is born. Gestational diabetes can, however, cause difficulties for you and your baby. The baby may be very large, and this may lead to the baby's shoulder getting stuck during birth and of injury to the mother. There is also a greater risk of having to have a caesarean or induced birth. The baby can be born too early and have less chance of surviving. The baby may also have jaundice and problems with breathing. Mother and baby are also more likely to get diabetes later in life.
In an attempt to prevent diabetes during pregnancy, women may be given advice to eat food with a low glycaemic index. Food with a high glycaemic index tends to raise your blood sugar quickly. Food with a low glycaemic index tends to raise your blood sugar slowly, giving your body more time to adjust to the increase in blood sugar.
Examples of high glycaemic index foods include some varieties of potato and highly processed food such as white bread. Low glycaemic index foods include fresh fruit, vegetables, and whole grain. Low glycaemic foods are often rich in fibre.
What does the research say?
Not all research provides the same quality of evidence. The higher the quality, the more certain we are about what the research says about an effect. The words will (high quality evidence), probably (moderate quality evidence) ormay (low quality evidence) describe how certain we are about the effect.
The studies showed that:
- Advice to follow a diet of low glycaemic foods may lead to fewer babies who are much larger than average at birth
- We are very uncertain whether this advice prevents gestational diabetes
- We are very uncertain whether this advice reduces the number of caesarean births
None of the studies measured the effect of dietary advice on the number of babies that were larger than 4000g at birth, or the number of babies that died during late pregnancy, childbirth or their first week of life.
Table of results
| What was measured | High glycaemic foods | Low glycaemic foods | Quality of evidence |
|---|---|---|---|
| Babies much larger than normal at birth | 33 per 100 | 3 per 100 (0 to 23 per 100)1 | Low |
| Gestational diabetes | We are very uncertain of the effect on gestational diabetes | Very low | |
| Caesarean birth | We are very uncertain of the effect on gestational diabetes | Very low | |
| Babies larger than 4000g at birth | Not measured in these studies | - | |
| Babies who died during late pregnancy, childbirth, or the first week of life | Not measured in these studies | - | |
1The numbers in the brackets show the range in which the actual effect could be.
Where does this information come from?
The Cochrane Collaboration is an independent global network of volunteers dedicated to summarizing research about health care.
This information is taken from this Cochrane Review: Tieu J, Crowther CA, Middleton P. Dietary advice in pregnancy for preventing gestational diabetes mellitus. Cochrane Database of Systematic Reviews 2008, Issue 2. Art. No.: CD006674. DOI: 10.1002/14651858.CD006674.pub2.
This summary was prepared by:
Gunn Vist and Claire Glenton, the Nordic Cochrane Centre's Norwegian branch, Norwegian Knowledge Centre for Health Services, on behalf of the Cochrane Complementary and Alternative Medicine Field, and with funding from the US National Center for Complementary and Alternative Medicine (NCCAM) of the US National Institutes of Health (grants number R24 AT001293).
Low GI diet compared to high GI diet for preventing gestational diabetes mellitus
Patient or population: patients with preventing gestational diabetes mellitus
Settings: Hospital in USA and clinic in Australia
Intervention: low GI diet
Comparison: high GI diet
Outcomes | Illustrative comparative risks* (95% CI) | Relative effect | No of Participants | Quality of the evidence | Comments | |
|---|---|---|---|---|---|---|
Assumed risk | Corresponding risk | |||||
Large for gestational age infants | 33 per 100 | 3 per 100 | RR 0.09 | 62 | low1,2 |
|
Macrosomia (greater than 4000 g babies) | See comment | See comment | Not estimable | - | See comment | None of the studies reportede on macrosomia |
Perinatal mortality | See comment | See comment | Not estimable | - | See comment | None of the studies reported on perinatal mortality |
Gestational diabetes | 3 per 100 | 1 per 100 | RR 0.31 | 62 | very low1,2 |
|
Caesarean birth | 20 per 100 | 25 per 100 | RR 1.25 | 62 | very low1,2 |
|
*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. Thecorresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk ratio
GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.
1 Quasi-randomised trial with large (11 %) losses to follow up in relation to the number of events
2 Only one small study, and wide confidence interval