Preterm delivery is associated with lower health chances after birth. Women with a migration background often have a higher preterm risk (less than 37 gestational weeks) compared to the nonmigrant majority population. In Germany, little is known about the scope and causes for more adverse birth outcomes among immigrant women. Focusing primarily on two large migrant groups, that is first-generation Turkish and ethnic German immigrants, we examine whether these groups experience elevated preterm risk, and, if so, whether resources (e.g., economic, cultural, and social capital), health behavior (e.g., smoking during pregnancy and low utilization of prenatal care), and/or maternal constitution (height) help to explain the observed inequality relations. For the analysis, we estimate multiple logistic regression models based on the SOEP's newborn questionnaire (years 2003 – 2011). Our findings show that preterm birth is more prevalent among Turkish and ethnic German immigrants compared to women without a migration background. As expected, accounting for maternal constitution and resources decreases the preterm risk for all migrant groups, while – unexpectedly – a mother's and a partner's language proficiency is rather irrelevant. Health behavior during pregnancy then has no further explanatory power. After adjustment for all factors, no significant preterm differences between migrants and the nonmigrant majority population are observed. JEL-Classification: I10