Birth prevalence

Birth prevalence is a special type of prevalence. Just like prevalence it's a proportion, in this case, the number of children born with a congenital anomaly compared to the total number of births.

Unlike normal prevalence, this can't be measured at any one point in time as births occur consecutively over a given period. Whether the baby has a defect is determined solely at the time of birth and birth prevalence is followed over a period of time sufficiently long to obtain a statistically significant result.

As the period of observation is often quoted, it's tempting but wrong to confuse birth prevalence with incidence; in fact the period only affects the total number of births that are inspected for defects.