Teen Childbearing as Cause or Effect?
A premise of most public discussions about teen fertility is that having a baby
as a teen leads to inferior outcomes for the mother and the child. Indeed, women
who give birth during their teenage years are more likely than other women to
drop out of high school, to remain unmarried, and to live in poverty. The children
of teenage mothers fare worse than other children on economic, social, and cognitive
dimensions (Hoffman and Maynard 2008). If teen childbearing causes large
adverse consequences, then the natural response is to consider policies that can have inferior outcomes regardless of when they give birth.
Providing free contraception, for instance, could (modestly) reduce the likelihood
of giving birth as a teen, but it does not alter the underlying calculus that leads
disadvantaged women to “drop out” of the mainstream climb toward economic
and social prosperity—the path of completing school, investing in human capital,
and putting marriage before motherhood.
This section reviews the most compelling evidence to date on whether teen
childbearing itself causes adverse outcomes for teen mothers and their children.11
We also review a related, important issue regarding “unintended” pregnancies.
A large share of teen (and nonmarital) births are reported by the mother to be
“unintended,” which would suggest that providing teens with better access to sex
education, contraception, and related policies could help them achieve their
“intended” goal of not becoming pregnant. However, we believe that many births
that are labeled as “unintended” actually reflfl ect a degree of ambivalence on the
part of the teen mother, in which case the policy prescription is less clear.
The Effect of Teen Childbearing on Mothers and their Children
To what extent are the inferior outcomes of teen mothers driven by the event
of having given birth as a teenager, as opposed to other factors, such as growing
up in disadvantaged circumstances? A comparison of the outcomes of women who
did and who did not give birth as teens is inherently biased by selection effects:
teenage girls who “select” into becoming pregnant and subsequently giving birth
(as opposed to choosing abortion) are different in terms of their background characteristics
and potential future outcomes than teenage girls who delay childbearing.
We know that girls who grow up in poverty are more likely to become pregnant
and to give birth as teenagers. Tabulating data from the 2003 Panel Study of
Income Dynamics, we report that in a sample of women age 20 to 35, 24 percent
give birth before age 20; but among the subsample of those women who were born
into poverty, 49 percent give birth before age 20 (Kearney and Levine 2010).
A number of authors have tried to isolate the causal effect of teenage
childbearing on subsequent outcomes, holding constant family background characteristics.
To isolate the effect of teen childbearing, Geronimus and Korenman
(1992) employ a “within-family” estimation approach that compares differences
in subsequent socioeconomic status of sisters who experienced their fifi rst births at
different ages. They analyze samples from three datasets: the National Longitudinal Survey Young Women’s Sample (NLSYW), the Panel Study of Income Dynamics
(PSID), and the 1979 National Longitudinal Survey of Youth (NLSY79). They
fifi nd that cross-sectional comparisons that do not control for detailed family background
greatly overstate the costs of teen childbearing. In fact, once background
characteristics are controlled for, the differences are quite modest. Furthermore,
even these modest differences likely overstate the costs of teen childbearing, since
the sister who gives birth as a teen is likely to be “negatively” selected compared
to her sister who does not. In addition to differences in observed and unobserved family background
characteristics, girls who are more committed to achieving higher levels of educational
attainment and economic success may be more committed to preventing a
pregnancy from occurring during their teenage years. Such girls may also be more
inclined to choose abortion if they do get pregnant. From a research perspective, we
ideally want to observe a sample of women who have the same potential outcomes
and the same inclination to get pregnant and give birth, but by random chance,
some do and some do not become teen mothers. A number of papers attempt to
exploit quasi-experimental variation in who becomes a teen mother to isolate the
causal consequences of teen childbearing.
Hotz, Mullen, and Sanders (1997) and Hotz, McElroy, and Sanders (2005)
exploit the fact that some women who become pregnant as teenagers experience
a miscarriage and thus do not have a birth. Their strategy essentially identififi es the
effect of delaying childbearing for women who become pregnant as teenagers.
Using data from the 1979 National Longitudinal Survey of Youth (NLSY79) on
women who were aged 13 to 17 between 1971 and 1982, the authors begin by replicating
previous fifi ndings of a correlation between teen childbearing and later life
outcomes.12 But when the authors of these studies employ their miscarriages “experiment,”
and thereby avoid confounding selection effects, none of the differences
are statistically signififi cant, and some are even reversed in sign. Hoffman (2008)
reexamines this data and fifi nds that the estimated impacts of a teen birth are more
negative for teen mothers who had births in the early 1980s relative to 1970s.13 Ribar
(1994) also employs an instrumental variables framework using the NLSY79 data.
He uses age at menarche in an instrumental variables framework, noting that earlier
age at menarche leads to more years at risk of becoming pregnant. The negative
consequences of teen birth for high school completion rate also seem to disappear
with this instrumental variable approach.