Differences in study design (prospective and retrospective), patient
populations (patients recruited from mental health settings and patients identified from registries), comparator groups (nondepressed
or depressed controls) and sample sizes make it difficult to
interpret the variability of findings. Many studies are also limited in
their ability to adequately control for important potential confounding
variables such as smoking, substance abuse, medical conditions
(such as pregnancy-induced hypertension and gestation diabetes)
and depression severity — all of which have been found to be
independently associated with adverse birth outcomes [10,11]