Hemoglobin Linked to Stillbirths

LINDSEY TANNER / AP 21nov00

Abstract below

CHICAGO — Women with high levels of hemoglobin in their blood early in pregnancy run an increased risk of stillbirths, a study suggests, offering a possible clue to a tragedy that often has no known cause.

In a Swedish study of 1,400 pregnant women, those with high hemoglobin levels early on faced nearly double the risk of having a stillborn child, which means a fetus delivered dead more than five months into pregnancy.

High levels of hemoglobin — an oxygen-carrying protein that gives red blood cells pigment — can be caused by smoking, which also has been linked to stillbirths. But this study found no clear association between smoking and hemoglobin and lacked data on what caused participants' high levels.

Other causes of hemoglobin can include heart defects and an overdose of iron supplements.

The findings, from Dr. Olof Stephansson and colleagues at the Karolinska Institute in Stockholm, were published in Wednesday's Journal of the American Medical Association.

Problems with the placenta and birth defects are among causes of the estimated 250,000 U.S. stillbirths each year, but in more than 80,000 cases, the causes are unknown.

The findings suggest that closely monitoring pregnant women with high hemoglobin levels could help prevent some of those deaths, said Dr. Nancy Green, associate medical director of the March of Dimes.

There is no treatment for many cases of high hemoglobin, but such women could be watched more carefully, and if there were signs that the fetus was in trouble, doctors could induce labor or take other steps.

Blood containing too much hemoglobin tends to be sticky and less able to flow through tiny blood vessels. That might disrupt blood flow to the placenta or developing fetus, Green said.

• JAMA: http://jama.ama-assn.org
• March of Dimes: http://www.modimes.org

Maternal Hemoglobin Concentration During Pregnancy and Risk of Stillbirth

JAMA v.284, n.20 22nov00

Olof Stephansson, MD; Paul W. Dickman, PhD; Anna Johansson, MSc; Sven Cnattingius, MD, PhD

Context  High and low maternal hemoglobin concentrations during pregnancy have been reported to increase risk of small-for-gestational-age (SGA) birth, which is a predictor of stillbirth. The relationship between hemoglobin concentration during pregnancy and risk of stillbirth is unclear.

Objective  To study the associations among hemoglobin concentration at first measurement during antenatal care, change in hemoglobin concentration during pregnancy, and risk of stillbirth.

Design, Setting, and Participants  Population-based, matched case-control study of births from 1987 through 1996 in Sweden including 702 primiparous women with stillbirths occurring at 28 weeks' gestation or later and 702 primiparous women with live births.

Main Outcome Measures  Risk of stillbirth, classified as malformed or nonmalformed, antepartum or intrapartum, preterm or term, and SGA or non-SGA, compared by maternal hemoglobin concentration at first antenatal measurement and weekly changes in hemoglobin concentration during pregnancy, adjusted for maternal age, body mass index, height, smoking, socioeconomic status, and week of first hemoglobin measurement.

Results  In multivariate analyses, compared with women with hemoglobin concentrations of 126 to 135 g/L at first antenatal measurement, women with concentrations of 146 g/L or higher were at increased risk of stillbirth (odds ratio [OR], 1.8; 95% confidence interval [CI], 1.0-3.3). This risk was slightly increased when the analysis was restricted to antepartum stillbirths without malformations (OR, 2.0; 95% CI, 1.1-3.8). When we further restricted the analyses to preterm and SGA antepartum nonmalformed stillbirths, the ORs increased to 2.7 (95% CI, 1.1-6.4) and 4.2 (95% CI, 1.3-13.9), respectively. Excluding women with preeclampsia and eclampsia further increased these risks. Average weekly change in hemoglobin concentration during early or late pregnancy was not significantly associated with risk of stillbirth, although a larger decrease in concentration tended to be protective. Anemia (hemoglobin concentration <110 g/L) was not significantly associated with risk of stillbirth in multivariate analyses (OR, 1.2; 95% CI, 0.5-2.7).

Conclusions  High hemoglobin concentration at first measurement during antenatal care appears to be associated with increased risk of stillbirth, especially preterm and SGA antepartum stillbirths.

JAMA. 2000;284:2611-2617

Author Affiliations: Department of Medical Epidemiology, Karolinska Institutet, Stockholm, Sweden.

Corresponding Author and Reprints: Olof Stephansson, MD, Department of Medical Epidemiology, Karolinska Institutet, PO Box 281, SE-171 77, Stockholm, Sweden (e-mail: olof.stephansson@mep.ki.se).

Author Contributions: Dr Stephansson contributed to the design of the study, was responsible for collection of the data, performed parts of the analyses, and took main responsibility in writing the manuscript.
    Drs Dickman and Johansson performed the statistical analyses and assisted in the interpretation of the results and writing of the manuscript. Dr Cnattingius developed the study and assisted in the interpretation of the results and writing of the manuscript.

Funding/Support: This study was funded by grants from The Swedish Council for Social Research (project 98-0265:1B) and Karolinska Institutet.