White moms’ low cholesterol, preemies linked
Pregnant white women who have abnormally low cholesterol levels are 21% more likely to give birth preterm, and both white and black women with low levels give birth to babies who weigh less than other infants of the same gestational age, researchers report today.
Obstetricians already knew that women with the highest cholesterol levels are more likely to give birth preterm, but this is the first evidence of risk at the other end of the spectrum, experts said.
“It appears that too little cholesterol may be as bad as too much cholesterol during pregnancy,” said Dr. Max Muenke of the National Human Genome Research Institute, the lead author of the paper in the journal Pediatrics. He cautioned that the study needed to be replicated before physicians took action in treating prospective mothers.
“At a practical level, this doesn’t mean that pregnant women need to start eating cholesterol,” said Dr. Michael Katz, acting medical director of the March of Dimes Foundation, who was not involved in the study. “The big question in my mind is whether this is a surrogate for something else, especially since it is only true for white women. The physiology is not that different” for whites and blacks.
The study “opens the door to the identification of a high-risk group in whom early interventions, including nutritional modifications . . . might be effective,” wrote Dr. Mario Merialdi of the World Health Organization and Dr. Jeffrey C. Murray of the University of Iowa Carver College of Medicine in an editorial accompanying the paper.
One in eight infants in the United States is born premature, defined as a gestational age of less than 37 weeks, according to a recent report from the National Academy of Sciences. A full term is 38 to 42 weeks.
Preterm births are responsible for a third of infant deaths in the United States and half of those who die in the first month of life, according to a report last October from the Centers for Disease Control and Prevention.
It is “the single largest factor worldwide in infant mortality and morbidity,” Merialdi and Murray wrote.
The premature infants who survive have a high incidence of developmental abnormalities, including cerebral palsy, cognitive impairment, blindness, deafness and respiratory illness.
Known risk factors for pregnant women, including smoking, stress, trauma, drug abuse, multiple births and infections, account for about half of premature births, but the causes of the rest are unknown, Katz said.
Muenke and his colleagues retrospectively studied 9,938 South Carolina women who had routinely been referred to clinics for second-trimester blood analyses. They eliminated those who smoked or had other known risk factors, leaving 118 women with low total cholesterol -- less than 160 milligrams per deciliter -- and 940 women with higher levels.
They found that 5% of the women with cholesterol levels in the normal range of 160 to 261 mg/dl had preterm deliveries. About 12% of both white and African American women with higher cholesterol levels had preterm births.
Among those with abnormally low cholesterol levels, 12.7% had preterm deliveries. But when the results were stratified by race, 21% of whites’ deliveries were preterm, compared with only 5% of blacks’.
Among both black and white women with low cholesterol who carried their babies full term, the infants weighed an average of 5 ounces less than those delivered to women with normal cholesterol levels.
“We found this quite surprising,” Muenke said. “We have two other studies underway to see if we can confirm it.”
One rationale for the finding is that cholesterol is required for the synthesis of the hormone progesterone, which is critical to the maintenance of pregnancy and is a key component of plasma membranes in the endometrium of the pregnant uterus, Merialdi and Murray said.
Preliminary studies have shown that progesterone supplements decrease the risk of preterm labor in some high-risk groups, they said, and the new findings may help explain why.
The study was funded by the National Institutes of Health.
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