Birth characteristics of women who develop gestational diabetes: population based studyBMJ 2000; 321 doi: http://dx.doi.org/10.1136/bmj.321.7260.546 (Published 02 September 2000) Cite this as: BMJ 2000;321:546
- a Locus for Registry-based Epidemiology, Department of Public Health and Primary Health Care, University of Bergen, N-5021 Bergen, Norway
- b Section for Medical Statistics, Department of Public Health and Primary Health Care, University of Bergen
- c Medical Birth Registry of Norway, University of Bergen
- Correspondence to: G M Egeland
- Accepted 5 April 2000
Women with gestational diabetes are at increased risk of non-insulin dependent diabetes and their babies are at increased risk of adverse perinatal outcomes.1 These risks can be reduced by better detection and control of diabetes.2 Identifying risk factors for gestational diabetes may improve screening programmes. As low birth weight has been related to non-insulin dependent diabetes in elderly populations,3 we decided to investigate whether women's characteristics at birth could predict their subsequent risk of gestational diabetes.
Subjects, methods, and results
We used linked generation data from the medical birth registry of Norway to study all women born in 1967–84 who had given birth between 1988 and 1998. The registry is a compulsory reporting system and files used for analysis are anonymised. Although there were 141 107 women in the cohort, we excluded 2393 who were not singletons.
We compared the birth characteristics of women with and without self reported gestational diabetes in one or more pregnancies. Data were analysed in relation to categories of birth weight; the ponderal index at birth (m/g3×100); gestational age (excluding women who were considered misclassified)4; weight for gestational age; and whether the woman had a mother whose pregnancy had been complicated by diabetes (any type), pre-eclampsia, eclampsia, placental abruption, or hypertension. We also considered diabetes in relation to the women's age and parity and their mothers' age and parity when they were born. We calculated odds ratios obtained from logistic regression analyses in which we adjusted for the women's age and parity and their mothers' diabetes.
Altogether 498 of these women aged less than 32 reported gestational diabetes. Prevalence increased with age, from 1.5 per 1000 deliveries for women aged ≤20 to 4.2 for women aged ≥30 (odds ratio 2.8; 95% confidence interval 1.9 to 4.3). Parity increased the risk of gestational diabetes; age adjusted odds ratios (95% confidence intervals) for women with two, three, and four or more deliveries compared with one delivery were 1.5 (1.2 to 1.9), 1.9 (1.4 to 2.5), and 3.3 (2.1 to 5.1) respectively.
Women whose mothers had had diabetes during pregnancy were at increased risk of gestational diabetes (table). The table also shows that there were significant inverse trends in diabetes in relation to birth weight and weight for gestational age (P<0.001). The increased risks of gestational diabetes were 80%, 60%, and 40% in women whose birth weights were ≤2500g, 2500–2999 g, and 3000–3499 g respectively compared with women in the 4000–4500 g group. We observed similar findings in relation to categories of weight for gestational age. Birth weight and weight for gestational age are strongly related; the three highest birthweight categories occur primarily in the three highest categories of weight for gestational age. We therefore limited further analyses of both variables to women whose birth weight was less than 3500 g. The inverse trend in diabetes in relation to weight for gestational age remained significant (table, P<0.01), but the variation attributed to the truncated range of birth weight was not significant. No other variables examined were associated with diabetes.
Low birth weight or low weight for gestational age or having a mother who was diabetic during pregnancy increases the risk of gestational diabetes. In women who weighed less than 3500 g at birth, weight for gestational age may provide additional predictive information on risk. No other birth characteristics were predictive of gestational diabetes. The non-significant raised risk in women weighing 4500 g or more at birth could indicate undiagnosed or unrecorded maternal diabetes. Low birth weight and low weight for gestational age may be common risk factors for gestational diabetes and non-insulin dependent diabetes. The results are compatible with the fetal origins of disease hypothesis.5 Future studies combining birth information with risk factors in adulthood may improve predictive models for identifying women at risk of gestational diabetes.
Barbro Mork Emblem was instrumental in linking the generational birth information and in setting up the generational analytical database.
Contributors: GE had the idea for the study, conducted analyses, and wrote the report. RS provided guidance in using the registry, discussed core ideas and study design, and edited the report. LI supervised data collection, discussed core ideas and study design, and edited the report. All authors are guarantors of the paper.
Funding Medical Birth Registry of Norway and Locus for Registry-based Epidemiology, University of Bergen.
Competing interests None declared.