Objective To estimate the effect of low maternal age on late fetal death an
d infant mortality and to estimate the extent of any increase in infant mor
tality attributable to higher rates of preterm birth among teenagers.
Design Population-based cohort study.
Setting Births recorded in the nationwide Swedish Medical Birth Registry.
Population All single births to nulliparous women aged 13-24 years (n = 320
,174) during 1973-1989.
Methods Using information recorded in the medical birth registry, linked to
a national education register, the effect of low maternal age on adverse o
utcomes was estimated using logistic regression analysis.
Main outcome measures Late fetal death, neonatal and postneonatal mortality
and preterm birth.
Results Compared with mothers aged 20-24 years, adjusted risks of neonatal
and postneonatal mortality were significantly increased among mothers aged
13-15 years (odds ratios = 2.7 and 2.6, respectively) and among those aged
16-17 years (odds ratios = 1.4 and 2.0, respectively), while mothers aged 1
8-19 years had a significant increase in risk of postneonatal mortality onl
y (odds ratio = 1.4). Rates of very preterm birth (less than or equal to 32
weeks), according to maternal age, were: 13-15 years, 5.9%; 16-17 years, 2
.5%; 18-19 years, 1.7%; and 20-24 years, 1.1%. The high rates of very prete
rm birth among young teenagers almost entirely explained the increased risk
of neonatal mortality in this group.
Conclusions The increased risks of neonatal and postneonatal mortality amon
g young teenagers may be related to biological immaturity. The increase in
risk of neonatal mortality is largely explained by increased rates of very
preterm birth.