Study Links Low Birth Weight to Miscarriage

A new study published in the Journal of Epidemiological Community Health suggests that women who have a history of abortions or miscarriage are three times more likely to give birth to infants with low birth weight. Since infants with low birth weights are more likely to suffer neonatal morbidity and mortality, this study alerts physicians to the potential risks factors leading to low birth weights.

The study defines a low birth weight as less than 2500 grams, or 5.5 pounds. Approximately half of all infants born with low birth weight are pre-term (before 37 weeks gestation). The remainder were below the tenth percentile for weights by their gestational dates.

Notably, the study did not differentiate between previous spontaneous abortion, or miscarriage, and previous induced abortion, regardless of the reason. The researchers also indicate that the reports of previous abortions are based solely on anecdotal evidence, namely voluntary reporting by mothers.

The study showed a significant association between abortion or miscarriage and low birth weight even after the data was adjusted for other factors such as race, maternal age, and smoking and alcohol use.

In addition to previous miscarriage and abortion, other factors that contributed to low birth weights include increasing maternal age after the age of 30, inadequate prenatal visits (less than 10 visits), and increased smoking. Weight loss and the lack of adequate weight gain during pregnancy were also significant risk factors for low birth weight, as was a BMI of less than 25.

The underlying cause of the correlation between miscarriage or abortion and low birth weight is unresolved. The researchers suggest that the risks associated with induced abortion vary depending on the mechanism used, such as vacuum aspiration, or other complications resulting from the abortion. In contrast, biological factors contributing to miscarriage may include cervical incompetence or associated genetic, immunological, infectious, or uterine abnormalities that could affect both a fetus' intrauterine growth and at what week the fetus is delivered. Unfortunately, the study does not examine these underlying causal factors.

What the evidence does suggest, however, is that women with three or more abortions are three times more likely to have a pre-term (before 37 weeks gestation) birth. These women were also nine times more likely than women with no previous abortion or miscarriage to have infants with low birth weight (less than 5.5. pounds pre-term) or low birth weight at term (low birth weight at 37 weeks of gestation or later).

Sources:

J Epidemiol Community Health, "Previous abortion and the risk of low birth weight and preterm births," J.S. Brown Jr., T. Adero, S.W. Masho.