TOPLINE:

Women with type 1 diabetes (T1D) who did not achieve optimal glycaemic control before conception faced a markedly higher, dose-dependent risk for preeclampsia, especially for its early and late preterm forms.

METHODOLOGY:

• Researchers conducted a population-based cohort study using data from Swedish nationwide health registers to assess the risk for preeclampsia in women with T1D.
• They included 1,689,301 singleton births between 2003 and 2019, including 4429 births to women with T1D and 1,684,872 births to women without the condition.
• The researchers focused on pregestational T1D, defined as the first diagnosis occurring within 91 days of conception and at least one A1c measurement recorded within 90 days before or after conception.
• The main outcome was the risk for preeclampsia, stratified according to gestational age at delivery as early preterm (< 34 + 0 weeks), late preterm (34 + 0 to 36 + 6 weeks), or term (≥ 37 + 0 weeks).

TAKEAWAY:

• Women with T1D were 4.7-fold more likely to develop preeclampsia than those without (adjusted risk ratio [aRR], 4.7; 95% CI, 4.4-5.0). The risk increased as glycaemic control worsened, with the aRR increasing from 3.4 (95% CI, 2.9-4.0) for A1c levels < 48 mmol/mol to 6.3 (95% CI, 5.3-7.7) for A1c levels ≥ 76 mmol/mol.
• The risk for early preterm preeclampsia was 7.2-fold higher in women with T1D than in those without (aRR, 7.2; 95% CI, 6.1-8.5), with the aRR increasing from 3.3 (95% CI, 2.0-5.4) to 13.3 (95% CI, 9.0-19.4) from lower to higher A1c categories.
• Similarly, the risk for late preterm preeclampsia was 9.9-fold higher in women with T1D than in those without (aRR, 9.9; 95% CI, 8.8-11.1), with the aRR increasing from 6.3 (95% CI, 4.7-8.4) to 15.1 (95% CI, 11.2-20.3) from lower to higher A1c categories.
• A similar pattern was observed with term preeclampsia in women with T1D.

IN PRACTICE:

"Maintaining optimal glycaemic control within target range around conception offers the lowest risk of preeclampsia among women with T1DM [T1D]," the authors wrote.

SOURCE:

This study was led by Natalie Holowko and Nathalie Roos, Clinical Epidemiology Division, Department of Medicine, Solna, Karolinska Institutet, Stockholm, Sweden. It was published online on August 26, 2025, in BJOG: An International Journal of Obstetrics & Gynaecology.

LIMITATIONS:

This study included only women whose A1c levels measured around conception, which may have introduced selection bias. Diagnosing preeclampsia in women with T1D who already had albuminuria presented additional complexity due to overlapping features. This study lacked data from continuous glucose monitoring.

DISCLOSURES:

This study was supported by Spädbarnsfonden; the Swedish Research Council for Health, Working Life and Welfare; the Swedish Research Council; and Region Stockholm. The authors declared having no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication