To construct the gestational‐age‐specific blood pressure curve and percentile blood pressure values of pregnant women in Jiangsu Province, and to explore the clinic significance of the blood pressure changes in women whose blood pressure was less than 140/90 mmHg (1 mmHg=0.133 kPa) in each trimester and eventually developed pregnancy induced hypertension (PIH) or pre-eclampsia (PE).

A prospective longitudinal cohort during pregnancy was built. Singleton pregnant women in the first trimester (11-13⁺⁶ weeks) were recruited from July 2017 to September 2020 in Nanjing Drum Tower Hospital, and were followed up in the second trimester (19-23⁺⁶ weeks), the third trimester (30-33⁺⁶ weeks) and approaching the expected date of delivery (35-38⁺⁶ weeks). The Viewpoint 6.0 software was used to record pregnancy-related information. The blood pressure was measured by standard methods in our clinic. Least mean square (LMS) function was performed to fit the gestational-age-specific blood pressure curve and percentile blood pressure values were calculated at every follow‐up time point. Logistic regression was applied to calculate the OR for the groups with blood pressure ≥95th percentile (P₉₅).

There were 3 728 singleton pregnant women invited in this study, including 3 490 normal pregnant women (93.62%, 3 490/3 728), and 238 pregnant women with PIH or PE (6.38%, 238/3 728). Gestational-age-specific blood pressure curve showed that systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) decreased in the second trimester, compared with those in the first and the third trimester, however the fluctuation of blood pressure was low, but regardless of the gestational age, P₉₅ of SBP, DBP and MAP increased by 14, 11 and 11 mmHg respectively, compared with 50th percentile (P₅₀). In the first trimester, the risk of developing PIH or PE finally in pregnant women with blood pressure ≥P₉₅ was 4.36-fold (95%CI: 2.99-6.35) for SBP than women with SBP<P₉₅, 5.22-fold (95%CI: 3.65-7.46) for DBP and 5.14-fold (95%CI: 3.61-7.32) for MAP. When approaching the expected date of delivery, the corresponding risks of the women with blood pressure ≥P₉₅ were 16.76 times, 27.45 and 27.31 times respectively than those of the women with blood pressure < P₉₅. In the first trimester, every 1 mmHg elevation of SBP the risk developing PIH or PE increased by 24% (OR=1.24, 95%CI: 1.15-1.33), 44% (OR=1.44, 95%CI: 1.31-1.59) for DBP and 47% (OR=1.47, 95%CI: 1.33-1.61) for MAP, respectively. The risk in the second trimester was similar to that in the first trimester, and in the third trimester, the risk was further increased. When approaching the expected date of delivery, DBP or MAP increased by 1 mmHg, the risk developing PIH or PE was double; while SBP increased by 1 mmHg, the risk increased by 58%. The areas under the receiver operator characteristic curves of SBP, DBP and MAP were similar for predicting PIH or PE, and the predictive efficiency were all poor.

Construction of percentile blood pressure values for pregnant women is helpful in identification of high-risk women of developing PIH or PE. The risk of PIH or PE in pregnant women with blood pressure ≥P₉₅ but <140/90 mmHg has significantly increased compared with women with blood pressure < P₉₅.

Pregnancy; Blood pressure; Hypertension, pregnancy-induced; Pre-eclampsia; Reference values; Cohort studies