What is a significant risk factor for preterm labor?

Multiple pregnancies, such as twins or triplets, are indeed a significant risk factor for preterm labor. This increased risk is due to the heightened demands on the mother's body when carrying more than one fetus, which can lead to uterine overdistension and increased contractions. Additionally, women with multiple pregnancies often experience complications such as gestational hypertension or preeclampsia, both of which can contribute to preterm labor.

In contrast, while advanced maternal age, low maternal weight, and a sedentary lifestyle can potentially pose risks to pregnancy, they are not as directly related to the likelihood of preterm labor in the same way that multiple pregnancies are. Advanced maternal age may lead to other complications, low maternal weight can affect fetal development, and a sedentary lifestyle may have various health implications, but extra uterine burden is a more immediate factor that influences the timeline of labor.