I think you saw a red band on the chart, which I am looking at as I type this, and thought that red band referred to "pregnancy, childbirth and other obstetric complications," when it is actually the red band that corresponds to "heart disease, hypertension, and other circulatory system disease." The legend for which disease category is which is helpfully arranged in the same vertical order in which mortality from diseases is cumulatively shown on the chart--that's why I'm sure the broad red band that has declined the most is heart disease rather than complications of pregnancy. (My reality check is that I know the approximate base rate of both causes of death during the time period shown on the chart, which corresponds to my lifetime.)