Preconception blood pressure and risk of preterm birth: a large historical cohort study in a Chinese rural population

Ying Yang, Ph.D., Yuan He, Ph.D., Qian Li, M.S., Yuanyuan Wang, Ph.D., Zuoqi Peng, M.D., Jihong Xu, Ph.D., Xu Ma, M.S.correspondenceemail

Objective

To examine the relationship between preconception blood pressure (BP) and the risk of preterm birth (PTB) using a historical cohort of reproductive-aged women and girls from a Chinese rural population.

Design

A historical cohort study established between 2010 and 2013 in People's Republic of China.

Setting

Local family-planning service agencies and maternal–child care service centers.

Patient(s)

A total of 367,425 reproductive-aged women and girls who participated in the National Free Pre-pregnancy Checkups in 2010–2012 and subsequently had a live birth before October 2013.

Intervention(s)

None.

Main Outcome Measure(s)

Incidence rates of PTB in reproductive-aged women and girls across preconception BP levels.

Result(s)

Preterm births were defined as babies born alive at 28 to 37 weeks of pregnancy. Compared with the participants with a systolic BP of <120 mm Hg, the multivariable-adjusted odds ratio (OR) for PTB was 0.99 (95% confidence interval [CI]: 0.95–1.03]), 1.21 (95% CI: 1.11–1.32), 1.47 (95% CI: 1.22–1.77), 1.80 (95% CI: 1.25–2.59), and 1.81 (95% CI: 1.20–2.73) for the participants with systolic BP of 120–129, 130–139, 140–149, 150–159, and ≥160 mm Hg, respectively. When the participants with normal BP were used as the reference, the adjusted OR for PTB was 1.04 (95% CI: 1.01–1.08), 1.38 (95% CI: 1.25–1.53), and 1.54 (95% CI: 1.21–1.97) for the participants with prehypertension, stage-1 hypertension, and stage-2 hypertension, respectively. In addition, isolated systolic and diastolic hypertension increased the risk of PTB by 55% and 30%, respectively.

Conclusion(s)

Our results indicated a strong linear and independent relationship between BP levels and the risk of PTB in Chinese reproductive-aged women and girls. Maternal hypertension before pregnancy can significantly increase the risk of PTB.

Fertility and Sterility

July 2015Volume 104, Issue 1, Pages 124–130