http://www.ajcn.org/content/72/1/241S.full
Causes of decline in maternal mortality after the mid-1930s
To answer the third question pertaining to the reason for the sudden decline in maternal mortality rates in the 1930s, it is necessary to look at changes in obstetric care. The initial impetus for the decline in maternal mortality rates was the introduction of sulfonamides, which were extremely effective against strains of Streptococcus pyogenes (the ß-hemolytic streptococcus, Lancefield group A), which was the cause of most deaths of puerperal fever (6, 11) as shown in Figure 3. Other factors that contributed to the reduction in maternal mortality rates were introduced gradually. They included the use of ergometrine, blood transfusions, and penicillin; better training; better anesthesia; improved organization of obstetric services; less interference in normal labors; and the decline in virulence of the streptococcus.

Maternal mortality, home deliveries, and midwives
Historical data show that maternal mortality rates were lowest for home deliveries undertaken by trained and supervised midwives with no exceptions. Two examples from a wide range of evidence are presented below (6).

The rural nurse midwives of the Queen's Institute of Nursing, which was an organization of highly trained and supervised midwives in England and Wales, kept meticulous records on all maternal deaths occurring at home or after transfer to a hospital. This organization was particularly active between the 1920s and 1940s and achieved very low rates of maternal mortality similar to, if not better than, the rates achieved in the northwestern European countries.

Similar low levels of maternal mortality were achieved during the 1920s and 1930s in the United States by a remarkable service in the history of maternal care that was founded by Mary Breckinridge. Midwives in the Kentucky Frontier Nursing Service traveled on horseback to assist with deliveries, which were all at home in a poor rural farming community with low living standards. Despite the poverty, maternal mortality rates were ≈10 times lower than those in the nearby city of Lexington and the United States as a whole (Table 1) (6).
High maternal mortality due to unnecessary interference
In contrast with the above findings, maternal mortality rates were very high in countries, states, regions, or areas where most deliveries were performed by physicians, especially in the hospital. Maternal mortality rates were also high when maximum surgical interference in normal or potentially normal labors was encouraged or advocated. A leading American obstetrician in the 1920s, Joseph Bolivar DeLee (13, 14), wrote a paper entitled "The prophylactic forceps operation" in which he advocated that procedures for ordinary deliveries be changed to include anesthetizing every patient in the second stage of labor, delivering the baby with forceps, and manually removing the placenta using the "shoehorn maneuver." His advice was heeded by many obstetricians and horrendous examples of iatrogenic mortality resulted. Another example, from Britain, was the widespread use of chloroform and forceps by general practitioners in uncomplicated deliveries between ≈1870 and the 1940s. This was described by one observer as a tendency a "little short of murder" (15) and accounted for many unnecessary deaths.

Maternal mortality and social class
Another unexpected finding related to maternal mortality, which was the basis for the second question raised at the beginning of this paper, was the inverse relation between maternal mortality rates and social class. Here the evidence comes almost entirely from Britain. Infant mortality is known to be strongly related to social class; the highest rates are found among the working classes, whereas the lowest rates are among the professionals. From at least the 1830s, however, the risk of dying in childbirth was higher in social classes I and II (the upper and professional classes, respectively) than it was in social classes IV and V (the skilled and unskilled laborers, respectively). An example of this is shown in Table 2, which gives data for 1930–1932 (16). The only plausible explanation for this social class difference is that the upper classes were more often delivered by physicians and, therefore, more likely to suffer unnecessary interference, whereas the lower classes were delivered by midwives, almost all of whom were trained by 1930–1932.