By Linda Carroll
(Reuters Health) – The number of women diagnosed with high blood pressure when they become pregnant or during the first 20 weeks of pregnancy has risen sharply in the U.S. over the last four decades, a new study suggests.
An analysis of the records of more than 150 million women who gave birth in U.S. hospitals found a 13-fold increase in hypertension rates between 1970 and 2010 overall, with the impact felt more strongly among African American women and older mothers-to-be, according to the results published in Hypertension.
One of the factors driving the increasing rates of hypertension in pregnant women may be the trend towards having children later in life, said the study’s lead author Cande Ananth, a professor and chief of the division of epidemiology and biostatistics in the obstetrics, gynecology and reproductive sciences department at Rutgers Robert Wood Johnson Medical School in New Jersey.
“There was a very, very striking advanced maternal age effect,” Ananth said. “Women are electing to postpone pregnancy. The mean age at which women become pregnant has increased by four to five years over a four-decade period. And we know that older maternal age is associated with hypertension.”
To take a closer look at hypertension trends, Ananth and his colleagues turned to the data from the National Hospital Discharge Survey compiled by the U.S. Centers for Disease Control and Prevention.
The researchers focused on hospitalizations for childbirth that occurred between 1970 and 2010. Included in the analysis were data from 151,554,325 delivery-related hospitalizations.
Among the women in the study, overall prevalence of chronic hypertension was 0.63%, with a two-fold higher rate among African American women (1.24%) compared with white women (0.53%). Rates of hypertension showed a steady increase with advancing maternal age among both African American and white women.
When the researchers looked at the data year by year, they found rates of chronic hypertension increased, on average, by 6% per year overall. White women experienced larger yearly increases averaging 7%, compared with 4% among African American women.
One surprising result was that rates of chronic hypertension did not appear to be affected by changes in obesity or maternal smoking.
Ananth advises women to work on their diets and overall health if they plan to become pregnant. “A balanced diet is incredibly important during pregnancy,” he said.
Rates of hypertension might be improved if women sought care from an obstetrician before they became pregnant, Ananth said. “Many don’t seek care until they know they are pregnant,” he added.
The new study highlights “a disturbing trend,” said Dr. Leena Nathan, an assistant clinical professor at the University of California, Los Angeles. “We’re seeing more high blood pressure in pregnant women, which can be dangerous to the moms’ and the babies’ health.”
When pregnant women have high blood pressure, “there are concerns ranging from the size of the fetus to the blood flow to the placenta not being as robust as it should be all the way to preeclampsia which can lead to seizures in the mom,” Nathan said.
Nathan, who wasn’t involved in the study, also attributes rising rates of hypertension to increasing numbers of women putting off childbearing. “I don’t think older age can explain it all, but it is a major risk factor. The body isn’t as healthy as you get older,” she said.
The new findings, especially those pertaining to African American women, did not surprise Dr. Priya Rajan, an associate professor in the division of maternal-fetal medicine at Northwestern University’s Feinberg School of Medicine in Chicago who wasn’t involved in the research. “We are starting to understand the impact a lifetime of stress that comes from just being black has on a woman’s health,” she said.
Rajan also wonders what the impact of missing information was on the study’s findings, noting that 19% of the women in the study population had no race data.