Association between parity and breastfeeding with maternal high blood pressure

OBJECTIVE: The objective of this study was to determine how parity and breastfeeding were associated with maternal high blood pressure, and how age modifies this association. STUDY DESIGN: Baseline data for 74,785 women were sourced from the 45 and Up Study, Australia. These women were 45 years of age or older, had an intact uterus, and had not been diagnosed with high blood pressure before pregnancy. Odds ratios (ORs) and 99% confidence intervals (CIs) for the association between giving birth, breastfeeding, lifetime breastfeeding duration, and average breastfeeding per child with high blood pressure were estimated using logistic regression. RESULTS: The combination of parity and breastfeeding was associated with lower odds of having high blood pressure (adjusted OR, 0.89; 99% CI, 0.82-0.97; P < .001), compared with nulliparous women, whereas there was no significant difference between mothers who did not breastfeed and nulliparous women (adjusted OR, 1.06; 99% CI, 0.95-1.18; P < .20). Women who breastfed for longer than 6 months in their lifetime, or greater than 3 months per child, on average, had significantly lower odds of having high blood pressure when compared with parous women who never breastfed. The odds were lower with longer breastfeeding durations and were no longer significant in the majority of women over the age of 64 years. CONCLUSION: Women should be encouraged to breastfeed for as long as possible and a woman's breastfeeding history should be taken into account when assessing her likelihood of high blood pressure in later life.