Pregnancy, pregnancy loss, and the risk of cardiovascular disease in Chinese women: findings from the China Kadoorie Biobank

Abstract

Background: Pregnancy and pregnancy loss may be linked to cardiovascular disease (CVD). However, the evidence is still inconsistent, especially in East Asians, whose reproductive patterns differ importantly from those in the West. We examined the associations of pregnancy, miscarriage, induced abortion, and stillbirth with CVD incidence among Chinese women.

Methods: In 2004-2008, the nationwide China Kadoorie Biobank recruited 302,669 women aged 30-79 years from ten diverse localities. During 7 years of follow-up, 43,968 incident cases of circulatory disease, 14,440 of coronary heart disease, and 19,925 of stroke (including 11,430 ischaemic and 2170 haemorrhagic strokes), were recorded among 289,573 women without prior CVD at baseline. Cox regression yielded multiple adjusted hazard ratios (HRs) for CVD risks associated with pregnancy outcomes.

Results: Overall, 99% of women had been pregnant, and among them 10%, 53%, and 7% reported having a history of miscarriage, induced abortion, and stillbirth, respectively. Each additional pregnancy was associated with an adjusted HR of 1.03 (95% confidence interval, CI: 1.02; 1.04) for circulatory disease. A history of miscarriage, induced abortion, and stillbirth, respectively, were associated with adjusted HRs of 1.04 (1.01; 1.07), 1.04 (1.02; 1.07), and 1.07 (1.03; 1.11) for circulatory disease. The relationship was stronger with recurrent pregnancy loss; adjusted HRs for each additional loss being 1.04 (1.00; 1.09) for miscarriage, 1.02 (1.01; 1.04) for induced abortion, and 1.04 (1.00; 1.08) for stillbirth.

Conclusions: Among Chinese women, increases in pregnancy, and a history and recurrence of miscarriage, induced abortion, and stillbirth are each associated with a higher risk of CVD.

Fig. 1

Adjusted hazard ratios (95% confidence intervals (CIs)) for incident circulatory disease associated with number of pregnancies and pregnancy losses. Analyses are stratified by age at risk and study area and adjusted for level of attained education, household income, smoking status, alcohol use, systolic blood pressure, history of hypertension, physical activity, body mass index, and history of diabetes. Analyses for pregnancy loss are additionally adjusted for number of live births. The hazard ratios are plotted on a floating absolute scale. Each square has an area inversely proportional to the standard error of the log risk. Vertical lines indicate the corresponding 95% CIs. Analyses for pregnancy loss are among women with at least one pregnancy

Fig. 2

Adjusted hazard ratios for incident circulatory disease per additional pregnancy (left) and induced abortion (right) by baseline characteristics. Adjustments are as in Table 2. Each square has an area inversely proportional to the standard error of the log risk. The diamond indicates the overall risk of circulatory disease per additional pregnancy and induced abortion and its 95% CI. Analyses for pregnancy and induced abortion, respectively, are among women with at least one pregnancy or at least one induced abortion

Fig. 3

Adjusted hazard ratios for incident circulatory disease per additional miscarriage (left) and stillbirth (right) by baseline characteristics. Adjustments are as in Table 2. Each square has an area inversely proportional to the standard error of the log risk. The diamond indicates the overall risk of circulatory disease per additional miscarriage and stillbirth and its 95% CI. Analyses for miscarriage and stillbirth, respectively, are among women with at least one miscarriage or at least one stillbirth