Psychosocial stress has been identified as a potential risk factor for preterm birth. However, an association has not consistently been found, and a consensus on the extent to which stress and preterm birth are linked is still lacking. A literature search was performed with a combination of keywords and MeSH terms to detect studies of psychosocial stress and preterm birth. Studies were included in the review if psychosocial stress was measured with a standardized, validated instrument and the outcomes included either preterm birth or low birth weight. Within the 138 studies that met inclusion criteria, 85 different instruments were used. Measures designed specifically for pregnancy were used infrequently, although scales were sometimes modified for the pregnant population. The many different measures used may be one factor that accounts for the inconsistent associations that have been observed.