WUNRN
The Lancet - March 2014
Women
older than 35 years had the highest maternal mortality ratios; and although
this pattern has been described before, no previous study has reported such
convincing data from such a wide range of countries.
Maternal Mortality by Age - Who Is Most at Risk?
The
estimated number of women who die each year from causes related to pregnancy or
childbirth has dropped substantially—from 543 000 deaths in 1990 to about
287 000 in 2010.1, 2 Nevertheless, maternal
mortality ratios remain among the least equitable of all health indicators,
ranging from less than five maternal deaths per 100 000 livebirths in
high-income countries to more than 500 per 100 000 livebirths in several countries
in sub-Saharan Africa.2
Sadly, most countries are expected not to achieve the maternal mortality target
set for the Millennium Development Goals.1
Identifying
high-risk groups is important for the design of intervention programmes. For
example, the risk of death is often stated to be twice as high for adolescent
mothers as for those in their 20s.3,
4 This statistic fits
well with the agenda of reducing adolescent childbearing, which is being
championed as a priority by international and bilateral agencies.4,
5
Nevertheless,
advocacy must be backed up by solid data. In The Lancet Global Health,
Andrea Nove and colleagues6 report the
results of an analysis of data from 144 countries, which together account for
93% of the world's annual births.6 The large and
diverse amount of data allowed for analysis of national age-specific estimates
of maternal mortality at a scale that was not previously possible.
Some
important findings emerge from this work. First, the risk of mortality
associated with adolescent pregnancy is only about a third higher than that of
women aged 20—24 years (260 [uncertainty 100—410] vs 190 [120—260]
maternal deaths per 100 000 livebirths), and therefore not as high as
previously believed. Second, women older than 35 years had the highest maternal
mortality ratios, and although this pattern has been described before, no
previous study has reported such convincing data from such a wide range of
countries. Third, age-specific maternal mortality varied substantially between
countries and regions; some showed the classic J-shaped curve for maternal
mortality ratio by age, whereas in others adolescents had the lowest maternal
mortality ratio of any age group. This group included several countries in
sub-Saharan Africa with very high maternal mortality ratios (eg, Central
African Republic, Democratic Republic of the Congo, and Zambia). Fourth, the
data source—vital registration or censuses and surveys—does not seem to affect
the overall conclusions. Finally, most uncertainty estimates for the 15—19
years age group overlap with those for mothers aged 20—24 years.
The
reasons behind these age patterns warrant further investigation. Previous
studies have shown that confounding by socioeconomic status is important in the
association between maternal age and several adverse perinatal outcomes, and a
descriptive study such as Nove and colleagues' analysis cannot take this issue
into account. For young mothers, who tend to be poorer and less educated than
older mothers in all types of settings, confounding will lead to increased
risks; for older mothers, confounding might mask even stronger associations in
many countries where older mothers tend to be better off.7
Parity also plays a part, since both nulliparous and high-parity women are
generally at increased risk of adverse maternal outcomes.8
Nove
and colleagues' findings also raise the issue of whether all adolescents have a
similar mortality risk. Analyses of maternal mortality ratios have
traditionally treated adolescents as a single age group (15—19 years), but this
approach could mask important differences related to biological maturity and
social conditions. Such a broad age group includes both very young mothers, for
whom childbearing has a high social and biological risk, and those aged 18—19
years, who are possibly in their prime biological—albeit not social—reproductive
status.8
Therefore, the risk for the 15—19 years age group is affected by the
proportions of younger or older adolescents within this group. Further analyses
could bring new insights into the age-gradient risk pattern for maternal
mortality.
These
results have to be interpreted with respect to present trends in age at
childbearing. Worldwide, adolescent fertility rates fell from 71 to 52 per
thousand women aged 15—19 years between the 1970s and the 2000s.9 This reduction
was seen in all regions, with the possible exception of Latin America. For
birth rates in women aged 35 years and older, substantial reductions were seen
in Africa, Asia, and Latin America, but slight increases were noted in
high-income countries.9
These patterns, taken together with Nove and colleagues' findings,6 suggest that
existing trends in age-specific fertility will contribute to a reduction in
maternal mortality in the near future.
Irrespective
of the size of the increased risk of maternal mortality for adolescents, many
overwhelming reasons exist for adolescent women to avoid early childbearing,
including the widespread adverse social, educational, and economic consequences
for young mothers.5
However, the most striking finding from Nove and colleagues' study6
is the very high risk for women older than 35 years. On the basis of these
data, delaying 100 000 adolescent pregnancies until ages 20—24 years would
prevent 70 maternal deaths, whereas more than 1000 deaths would be prevented if
100 000 pregnancies currently in women aged 40 years or older occurred
when the same women were in their early 20s. Whereas late motherhood in
high-income and middle-income countries might be an unavoidable consequence of
the broadly positive improvement of women's role in society, in low-income
countries many maternal deaths could still be prevented by improving access to contraception
to reduce unplanned, high-parity births.10