Introduction
Preterm birth (PTB) and low birthweight (LBW) are related to perinatal
mortality, and have been associated with a wide range of adverse
developmental outcomes for children.1 Recently, much
focus has been on the potential impact of maternal distress and anxiety
on birth outcomes. Studies have reported that the prevalence of maternal
anxiety during pregnancy varies from 6.6 to 10.4%.2,3Further, maternal anxiety during pregnancy is associated with
birthweight and gestational age.4,5 Prenatal anxiety
is recognized as a potential risk factor for PTB and
LBW.6,7,8
While associations between prenatal maternal anxiety and PTB and LBW
have been reported, causal inferences are only tentative. For several
reasons, randomization of anxiety or distress during pregnancy cannot be
conducted.9 Thus, in humans, investigations are
limited to observational designs. Using this methodology, associations
between prenatal maternal anxiety and PTB and LBW have been established.
New approaches to estimate the effects of prenatal maternal anxiety on
childhood outcomes are crucial in advancing the
field.9,10
In this study, we estimate the effects of degree (no symptoms, light
symptoms and severe symptoms) and timing of prenatal maternal anxiety on
infant birthweight and preterm birth. Timing was accounted for by
examining whether symptoms were reported at either or both of the
17th or 30th gestational weeks. We
test these associations using a sibling comparison design. The design,
which involves studying birth outcomes following differential exposure
to anxiety during pregnancy across siblings, has been found to reduce
the extent of the impact of family-level confounding
factors.9-11 on examinations of prenatal anxiety
effects.