Glycaemic Control in Women With Type 1 Diabetes and Preeclampsia Risk: A Nationwide Cohort Study

Objective No large‐scale studies exist investigating glycaemic control around conception and preeclampsia risk. Design Population‐based nationwide cohort study using the National Diabetes Register and other health registers. Setting Sweden. Population Singleton pregnancies between 2003 and 2019 ( N = 1 689 301); 4429 with type 1 diabetes (T1DM) and 1 684 872 without. Methods The main exposure was having a pre‐gestational diagnosis of T1DM (first diagnosis anytime ≤ 91 days after conception and ≥ 1value of glycated haemoglobin (HbA1c) within ±90 days from conception). Peri‐conceptional glycaemic control was categorised using the most recent HbA1c measurement (mmol/mol: < 48; 48–61; 62–75; ≥ 76). Unexposed were women without any diabetes diagnosis (≤ 91 days after conception). Main Outcome Measures Preeclampsia was defined using ICD codes and further categorised according to completed gestational weeks at delivery with preeclampsia diagnosis: early preterm preeclampsia (< 34 + 0), late preterm preeclampsia (34 + 0 to 36 + 6), or term preeclampsia (≥ 37 + 0). Results 16.8% of women with T1DM developed preeclampsia, compared to 2.9% of women without diabetes (adjusted RR [aRR] 4.7, 95% CI 4.4–5.0). Preeclampsia risk increased with peri‐conceptional HbA1c, from 11.6% in women with HbA1c < 48 mmol/mol to 23.3% in women with HbA1c ≥ 76 mmol/mol. Compared to unexposed women, there was a dose–response relationship between HbA1c and preeclampsia in women with T1DM (HbA1c < 48 mmol/mol aRR 3.4 (2.9–4.0); HbA1c 48–61 mmol/mol aRR 4.6 (4.2–5.1); HbA1c 62–75 mmol/mol aRR 5.7 (5.0–6.5): HbA1c ≥ 76 mmol/mol aRR 6.3 (CI 5.3–7.7)). Compared to unexposed women, the aRR of term preeclampsia was 3.5 times higher (3.1–3.9) in women with T1DM, while the aRR was much higher for early preterm preeclampsia (aRR 7.2: 6.1–8.5) and late preterm preeclampsia (aRR 9.9: 8.8–11.1). Conclusions Women with T1DM had a higher risk of preeclampsia, which increased in a dose–response manner with poorer peri‐conceptional glycaemic control.