In clinical practice, infants born after 28 weeks but before 37 weeks of pregnancy are considered preterm. The survival rate of these babies varies; the earlier the birth, the lower the likelihood of survival. Clinically, babies born at 23 weeks have a 17% chance of survival; those born at 24 weeks have a 39% survival rate; at 25 weeks, the rate is 50%; at 26 weeks, it increases to 80%; and at 27 weeks, it rises to about 90%. Babies born between 28 and 31 weeks have an even higher survival rate, approximately 95%; and from 32 to 33 weeks, the survival chances are comparable to those of full-term babies. Records indicate that the earliest preterm baby to survive was born at 21 weeks and five days, in Canada.