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Women's Health

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Low Birthweight PORT links high maternal ferritin levels during the second trimester with preterm birth

Women who have too high a level of ferritin in their blood (usually a measure of serum iron) during the second trimester of pregnancy are three times more likely to deliver preterm infants than other women, according to a study by the Low Birthweight Patient Outcomes Research Team (PORT), which is supported by the Agency for Health Care Policy and Research (PORT contract 282-92-0055).

Growing evidence indicates that preterm birth is associated with upper genital tract infections. The PORT investigators suggest that elevated serum ferritin, which has been linked to acute and chronic infections, may be an acute-phase reactant (a substance that increases or decreases in conjunction with inflammatory processes) associated with an upper genital tract infection in these women. Ordinarily, serum ferritin decreases after the 16th week of gestation.

The PORT researchers, led by Robert L. Goldenberg, M.D., of the University of Alabama at Birmingham, evaluated the relationship between spontaneous preterm delivery and infections such as acute-phase reactants, levels of maternal iron, and protein status. They obtained serum samples at 24 weeks gestation from 94 economically disadvantaged pregnant women.

Women with serum ferritin levels at least 42.0 mg/L had three times greater odds of delivering earlier than 32 weeks compared with women whose serum ferritin levels were lower than this value. This three-fold greater risk of preterm birth remained even after other contributing factors, such as maternal age, race, and history of a previous low birthweight infant, were taken into account. The other indexes of iron status and acute-phase reactants (for example, C-reactive protein) were not significantly associated with gestational age at birth. The effect of iron deficiency anemia on pregnancy outcomes was conflicting. Neither serum copper nor zinc concentrations were associated with gestational age at birth, according to the researchers.

In a related editorial, Dr. Goldenberg points out that babies born to women who are obese before becoming pregnant may not benefit from maternal dietary supplementation with trace metals or vitamins as do babies born to thinner women. He notes that previous studies by the Low Birthweight PORT have shown that the increase in fetal growth due to maternal zinc supplementation occurs predominantly in lean mothers.

Also, two recent studies carried out by others (Shaw, Velie, and Schaffer, JAMA 275(14):1093-1096, 1996; Werler, Louik, Shapiro, et al., JAMA 275(14):1089-1092, 1996) show that folic acid supplementation around the time of conception reduces incomplete closure of the fetal neural tube (neural tube defects, NTDs) at around 4 weeks' gestation in lean but not obese women, and that obesity itself is a risk factor for NTDs. However, folic acid, even in large quantities, may not be able to overcome other as yet unknown factors that may be associated with an increase in NTDs in the infants of obese women.

For more details on the study or editorial, see "Serum ferritin: A predictor of early spontaneous preterm delivery," by Tsunenobu Tamura, M.D., Dr. Goldenberg, Kelley E. Johnston, B.S., and others, which appears in the March 1996 Obstetrics & Gynecology 87(3), pp. 360-365; and "Prepregnancy weight and pregnancy outcome," by Dr. Goldenberg, in the April 10, 1996, issue of the Journal of the American Medical Association 275(14), pp. 1127-1128.

Hypertension among pregnant black women contributes to poor birth outcomes

Pregnant black women have more than twice the rate of chronic hypertension than women of other races. This may contribute to the greater incidence of low birthweight, preterm deliveries, and infant sickness and death among black women in the United States, according to a recent study by a team of researchers from the Agency for Health Care Policy and Research-supported (HS07400) MEDTEP Minority Research Center at Morehouse School of Medicine in Atlanta, GA. They found that hypertensive black women are at three-fold greater risk of hemorrhaging before delivery (antepartum hemorrhage) than black women whose blood pressure is within normal limits, an association not seen among other U.S. women. This hemorrhaging can be caused by premature separation of the placenta, placenta previa (a condition in which the placenta blocks the cervix), blood clotting problems, or other problems.

The researchers analyzed medical records data from the National Hospital Discharge Survey for the period 1988-1992 and found that the incidence of pregnancy-induced hypertension was 38.2 per 1,000 deliveries among all U.S. women who delivered babies in a hospital during the study period, and that black women accounted for 18 percent of all 628,933 deliveries in which the mothers were hypertensive. The incidence of hypertension among black women was 64.2 per 1,000 deliveries compared with 48.6 per 1,000 deliveries for other women. The rate of chronic hypertension preceding pregnancy was about 2.5 times higher among black women (25 per 1,000 deliveries) compared with other women (10.5 per 1,000 deliveries). Chronic hypertension is more likely than pregnancy-induced hypertension to lead to pregnancy complications. For example, development of late pregnancy toxemia, which can lead to convulsions and coma (preeclampsia and eclampsia), was about four times higher among women with chronic hypertension preceding pregnancy.

See "Maternal hypertension and associated pregnancy complications among African-American and other women in the United States," by Aziz R. Samadi, M.D., M.P.H., Robert M. Mayberry, M.P.H., Ph.D., Akbar A Zaidi, Ph.D., and others, in the April 1996 issue of Obstetrics & Gynecology 87(4), pp. 557-563.

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