During the third trimester normal Braxton Hicks contractions increase in frequency and intensity. They may even become uncomfortable and cause you to worry that you are going into premature labor. How to tell if it’s preterm labor: True labor contractions show a definite pattern. Employ the 1-5-1 formula: if your contractions last at least one minute, are five minutes (or less) apart, and continue for at least one hour you are, most likely, in labor. (This would mean you should alert your healthcare provider immediately.) Braxton-Hicks contractions come and go and don’t settle into a regular pattern. Don’t forget to practice relaxing and breathing with these trial-run contractions.