Background Chronic hypertension (CH) has been linked with adverse pregnancy outcomes, but it is unclear whether these associations are changing by maternal characteristics or over time.

The objective of this study was to examine the association between maternal CH and adverse pregnancy outcomes, and to determine whether the risk varies over time. We also aimed to assess the associations according to maternal age (younger or ≥ 35 yrs.) and other maternal characteristics.

Methods This population-based cohort study included women who had singleton births in Sweden between 1982 and 2012. Using data from the Medical Birth Register, we identified 2,777,045 babies born to 1,417,903 mothers during the study period. Of those 9,334 were born to women with CH. Maternal CH were recorded using ICD-8, ICD-9 and ICD-10. Outcome measures were pre-eclampsia (PE), emergency and elective caesarean sections (CS), spontaneous preterm birth (PTB<37 weeks’ gestation), medically indicated PTB, stillbirth and small for gestational age. Multivariate logistic regression models were performed using Stata 16 and adjusting for several socio-demographic and perinatal confounders.

Results Compared to normotensive women, we found higher odds among hypertensive women of the following outcomes: PE adjusted odds ratio [aOR (95% confidence intervals)]: [4.60 (4.31, 4.92)]; emergency CS [1.64 (1.53, 1.77)]; elective CS [1.63 (1.51, 1.76)]; medically indicated PTB [3.36 (3.11, 3.63)]; stillbirth [1.62 (1.26, 2.08)] and SGA [2.33 (2.13, 2.54)]. Moreover, Women of advanced maternal age were more likely to have emergency CS [aOR: 1.82 (1.61, 2.05)]; elective CS [1.83 (1.64, 2.04)]; medically indicated PTB [4.01 (3.54, 4.54)] and SGA [2.61 (2.24, 3.04)] compared to younger normotensive women. However, the magnitude of these associations appears to decrease over time apart of the association with PE which appears to have remained almost constant over time.

Conclusion Women with chronic hypertension are at increased risk of adverse maternal, fetal and neonatal outcomes and the risk differs according to maternal age. However, the effect of antihypertensive treatment and severity of hypertension have not been taken into account in this study.