Variations in gestational length and preterm delivery by race, ethnicity and migration

- Preterm delivery (PTD) rates vary by race/ethnicity and migrant status; however, disparities are poorly understood.
- The higher risk of PTD found among US-born, but not foreign-born Blacks, reflects lasting disadvantage.
- Studies of migrants suggest that environmental influences drive the PTD rate.
- Comparisons should be based on standardized pregnancy dating to avoid bias.
- Race/ethnicity or country of origin may serve as flags for further individual inquiry.

Preterm delivery rates within industrialized countries have been reported to vary according to the parents' race, ethnicity and migrant status; however, such disparities are poorly understood. In this paper, the available evidence and potential clinical significance of racial/ethnic and migrant disparities in gestational length and preterm delivery are assessed alongside potential explanatory factors. Although measurement bias in gestational length has the potential to inflate disparities, there is a consistently higher risk of preterm birth among some racial/ethnic groups. These differences most likely reflect lasting socio-economic disadvantage and discrimination rather than genetic mechanisms. The effect of migrant status is less conclusive due to heterogeneity of populations and the healthy migrant effect; however, environmental influences in the receiving country are implicated in driving increases of overall preterm rates. When assessing preterm delivery rates across ethnic and migrant groups, the use of standardized, ultrasound-based pregnancy dating methods is crucial to minimize bias. Current evidence does not justify the provision of a different clinical care approach to minority or immigrant women solely based on their race, ethnicity or country of origin; however, these labels may serve as flags for further inquiry on individual risk factors and a detailed obstetric history.