Blood pressure in the second and third trimesters of pregnancy and adverse pregnancy outcomes in singleton pregnancies: A bidirectional cohort study

Background

Although blood pressure in singleton pregnancies is related to multiple adverse pregnancy outcomes, the blood pressure threshold has been controversial.

Objective

To explore the blood pressure reference threshold of singleton pregnant women in the second and third trimesters.

Study design

A bidirectional single-centre cohort study was undertaken. Clinical data were collected for women with singleton pregnancies who underwent regular antenatal examinations and delivered at Peking Union Medical College Hospital between July 2020 and June 2023. Blood pressure was recorded at 20–24 and 28–32 weeks of gestation, and hypertension and pre-eclampsia were used as the primary outcomes. The percentiles of blood pressure were calculated, and the 95th percentile was used as the upper limit for the second and third trimesters of pregnancy. Poisson regression was used to calculated adjusted relative risk (aRR) and 95 % confidence intervals (CI) were used to analyse the relationship between elevated blood pressure and adverse pregnancy outcomes, and to further explore the impact of changes in blood pressure in the second and third trimesters on pregnancy outcomes. p-values < 0.05 were considered to indicate significance.

Results

In total, 7854 pregnant women with singleton pregnancies were included in this study. For pregnant women who did not experience adverse outcomes related to blood pressure, the 95th percentiles of systolic and diastolic blood pressure in the second trimester were 131 mmHg and 80 mmHg, respectively. Corresponding data for the third trimester were 130 mmHg and 80 mmHg, respectively. Therefore, 130/80 mmHg was taken as the upper limit of blood pressure. After excluding confounding factors, regardless of trimester, the risks of gestational hypertension, pre-eclampsia, preterm birth, low birth weight and neonatal intensive care unit (NICU) admission were found to be significantly higher in pregnant women with elevated blood pressure (p < 0.05). Pregnant women with sustained elevated blood pressure (i.e. in both the second and third trimesters) had aRR values for gestational hypertension, pre-eclampsia, premature birth, low birth weight and NICU admission that were 19.08 (95 % CI 13.04–28.03; p < 0.001), 11.43 (95 % CI 6.94–18.64; p < 0.001), 2.53 (95 % CI 1.83–3.42; p < 0.001), 2.98 (95 % CI 2.05–4.21; p < 0.001) and 1.79 (95 % CI 1.29–1.79; p < 0.001) times higher than those of normotensive pregnant women, respectively.

Conclusion

The blood pressure threshold of singleton pregnant women in the second and third trimesters is 130/80 mmHg. Sustained elevated blood pressure is harmful to the health of mothers and infants. Management and monitoring should be strengthened for pregnant women with elevated blood pressure.