Pregnancy-Induced Hypertension has Long-Term Health Implications for Both Mother and Child
Journal: Journal of the American Heart Association
Date: April 2020
Summary
Preeclampsia is a condition of persistent hypertension that some women develop during pregnancy or in the postpartum period. Preeclampsia is a more severe form of pregnancy-induced hypertension (high blood pressure). Five to eight percent of all births in the United States are impacted by preeclampsia, which used to be called “toxemia”. Most women with preeclampsia will deliver healthy babies and fully recover. However, some women experience complications - several of which may be life-threatening to mother and/or baby. If not properly recognized and managed, preeclampsia can progress to eclampsia, a very severe complication that includes the sudden onset of grand mal seizures and sometimes death. The rate of preeclampsia in the United States has increased by 25 percent in the last two decades, and is a leading cause of maternal and infant illness and death. It occurs more commonly among women of color.
Women who’ve had preeclampsia are three to four times more at risk for high blood pressure later in life, and have double the risk for heart disease and stroke. They also have an increased risk of developing diabetes. It’s unknown whether these risks are caused by preeclampsia itself, or if the women were already predisposed, but they first emerge in the years following a complicated pregnancy such as one with preeclampsia. Moore Institute Director Kent Thornburg, Ph.D., was invited to write a commentary on a recent study published in the April edition of the Journal of the American Heart Association. The study suggests maternal hypertension and preeclampsia are not only potential warnings for heart disease risk in the mother – but also in the offspring. This research brief provides an overview of the journal study and Dr. Thornburg’s analysis.
New information
What hadn’t been known before is the degree to which maternal hypertension affects the development of her baby’s heart before birth. In order to understand this, researchers at Oxford University used echocardiography to measure the hearts of 134 infants born at term, and then again at three months of age. Fifty-four of the infants’ mothers did not develop hypertension in pregnancy and 80 either developed pregnancy-induced hypertension, or the more severe form, preeclampsia. They discovered that the heart's right ventricle was 20 percent smaller than normal at birth in infants born to hypertensive mothers. This deficit persisted at three months. It also showed evidence of changes in the thickness of the hearts’ ventricle walls at three months of age: the left ventricle walls were eight percent thicker, and the right ventricle walls were 23 percent thicker in babies born to hypertensive mothers, than those whose mothers didn’t have hypertension.
But what’s the biological connection between pregnancy-induced hypertension and altered cardiac growth in the baby? The short answer is, we don’t know. However, this is where studies on the developmental origins of health and disease- comes in.
The placenta
The role the placenta plays in preeclampsia is unclear, but evidence has shown that poor blood flow to the placenta can lead to chemical stress within the placenta and to fetal tissues. In addition, a poorly constructed arrangement of blood vessels in the placenta increases the resistance that the developing baby’s heart must face in pushing blood through the placenta to obtain nutrients and oxygen. This high placental resistance is common among babies whose intrauterine growth is slow. This leads to high blood pressure in the baby and changes in the anatomy of the developing heart. High blood pressure in the baby also results in fewer heart muscle cells at birth.
But why did the hearts of babies born to mothers with hypertension grow abnormally over the first three months after birth when they are no longer attached to the mother? Thornburg speculates the total resistance that was needed to maintain normal flow was higher in the babies born to mothers with higher blood pressure and led to changes in the growth of the fetal ventricles that worsened during the first three months of life.
Conclusion
On the basis of this recent study, in combination with extensive animal studies, Thornburg speculates that babies born to mothers who have pregnancy-induced hypertension will have elevated risk for coronary heart disease and/or heart failure later in life. This finding is one more important clue toward solving the mystery of why a medical condition in a mother during pregnancy can lead to disease risk in her offspring.
The OHSU Bob and Charlee Moore Institute for Nutrition & Wellness supports human research that seeks to find the links between maternal stresses, including poor nutrition, and elevated disease risks for babies as they become adolescents and adults.
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Thornburg, K.L., Drake, R., Valent, A.M. (2020). Maternal Hypertension Affects Heart Growth in Offspring. Journal of the American Heart Association, 9(9), e016538, https://doi.org/10.1161/JAHA.120.016538