Healthy infants who survive their first month of life and who are born to adolescent mothers are at greater risk of dying within their first year than are comparable infants whose mothers are aged 23-29.¹ National data for 1996 and 1997 indicate that between 28 and 365 days after birth (i.e., in the postneonatal period), healthy infants died at a rate of 1.4 per 1,000 full-term births. Infants born to women aged 15 or younger had a substantially higher postneonatal mortality rate (3.2 per 1,000) than those born to 23-29-year-olds (0.8 per 1,000). As a result, the odds of postneonatal death, adjusted for a variety of factors that may affect infant health, were significantly increased among the former relative to the latter (odds ratio, 3.0). The risk declined steadily as mother's age increased.

Infant mortality rates are known to be higher than average among babies born to teen-agers, often because of neonatal deaths related to preterm delivery and low birth weight. This is especially true for infants born to very young mothers (those aged 15 and younger). Past research has focused little, however, on mortality among babies born relatively healthy and surviving beyond the first month of life.

To address this shortcoming, investigators studied comprehensive birth data from 1996 and 1997 that linked birth certificates with infant death certificates. The analysis was restricted to singleton first births among mothers aged 12-29. To minimize the effects of infants' health status at birth, the researchers focused on babies who were born at 37 or more weeks of gestation and who weighed at least 2,500 g at birth; they eliminated those who did not survive the neonatal period and those with congenital anomalies. Analyses were limited to white, black and Mexican American infants. The researchers used logistic regression analysis to determine the risk of postneonatal mortality, after adjusting for the effects of a variety of potentially confounding factors.

Among more than 1.8 million births in the two years under study, a total of 2,516 infants died during the postneonatal period, for a mortality rate of 1.4 deaths per 1,000 births. This rate was highest among babies born to mothers aged 15 and younger (3.2 per 1,000) and lowest among those born to women aged 23-29 (0.8 per 1,000). Rates differed slightly among infants born to white, black and Mexican American women, but in each group, the general pattern of decreasing rates with increasing maternal age was seen.

Teenagers were considerably more likely than older women to be unmarried and to have had inadequate prenatal care. After adjusting for the effects of these factors, as well as race and ethnicity, the investigators found that relative to infants born to women aged 23-29, babies born to the youngest mothers had the highest odds of postneonatal mortality (odds ratio, 3.0). The risk also was significantly elevated in other maternal age-groups, although odds ratios decreased steadily, from 2.4 among infants born to women aged 16-17 to 2.0 among those born to women aged 18-19 and 1.5 among those born to women aged 20-22.

Hypothesizing that single mothers have less social support than married mothers, and that this difference may affect their infants' health, the researchers also examined the risk of postneonatal death among infants born to unmarried women. After adjusting for the effects of adequacy of prenatal care and acknowledgment of the father on the birth certificate, they observed that for infants born to single white and black women, the risk of postneonatal mortality was elevated if the mothers were 15 or younger (odds ratios, 2.4 and 2.1, respectively), remained significantly elevated if the mothers were older teenagers (1.5-1.9) and were only marginally raised if the mothers were in their early 20s. Among infants born to Mexican Americans, the risk was significantly increased only for those with the youngest mothers (2.0).

To shed further light on the differences in postneonatal mortality by maternal age, the researchers focused on mortality resulting from potential neglect or abuse (56% of deaths during the study period).* Rates of postneonatal mortality from these causes followed the same pattern as overall rates, being highest among children of the youngest mothers (1.8 per 1,000) and falling steadily through older maternal age-groups. Among infants born to white and black women, the odds of postneonatal mortality from these causes (adjusted for use of prenatal care and marital status) were highest (odds ratios, 4.0 and 3.8, respectively) for offspring of the youngest women and declined but remained significantly elevated for those born to older teenagers and 20-22-year-olds. For children of Mexican American women, the risk was significantly elevated only if the mother was 17 or younger.

The researchers comment that relying on vital statistics gave their study substantially more analytic power than previous research, but left them unable to examine the effects of potentially important socioeconomic factors that are not routinely reported on birth certificates, particularly mothers' education and poverty status. Additionally, they note that because they studied only healthy infants, overall postneonatal mortality rates are likely to be higher than rates reported in the analysis.

"There is reason to be concerned about the children born to early adolescent mothers," the investigators conclude. They argue that because "a seemingly healthy infant born to an adolescent mother has a significantly lower chance of living to celebrate a first birthday than an infant born to an older mother," efforts to provide support to very young mothers and their infants should not be limited to prenatal and perinatal care, but should include broader postnatal support services.--M. Klitsch

REFERENCE

1. Phipps MG, Blume JD and DeMonner SM, Young maternal age associated with increased risk of neonatal death, Obstetrics & Gynecology, 2002, 100(3):481-486.