How long do normal contractions last before possibly leading to fetal distress?

Normal contractions during labor typically last between 30 to 90 seconds. When a contraction exceeds this duration, particularly reaching around 90 seconds or more, there is an increased risk for potential complications, including fetal distress. This is due to the fact that longer contractions can reduce the blood flow to the fetus as the uterus tightens, leading to decreased oxygen supply.

In the context of labor, the duration and intensity of contractions are crucial for both maternal and fetal well-being. It's important for healthcare providers to monitor contraction patterns closely for any signs that could indicate the fetus is not tolerating the stress of prolonged labor well. Thus, the 90-second duration marks a critical threshold, beyond which vigilance is necessary to assess for fetal distress.