I felt the need to back up my assertion that post-partum infection was, at the time, the most common cause of maternal mortality.
From a description of the book The Tragedy of Childbed Fever, by Irvine Loudon:
Childbed Fever, or as it soon became known, “puerperal fever”, was by far the most common cause of maternal mortality throughout the Western World until the late 1930s. It was an infection of the uterus following childbirth, which rapidly spread into the peritoneal cavity causing agonising peritonitis, and into the bloodstream causing septicaemia or “blood poisoning” which was almost invariably fatal…Most cases of puerperal fever were sporadic, but the most frightening form were the epidemics, which swept through “lying-in” (i.e. maternity) hospitals and also through towns and villages where it could suddenly appear without warning. In epidemics, fatality rates were often as high as 80 per cent…Almost all fatalities due to puerperal fever were due to one microorganism, the Group A Streptococcus, which is also the cause of scarlet fever, erysipelas and several other conditions…Puerperal fever, before World War II, was universally acknowledged to be by far the greatest problem in obstetrics…
And from another review of the same book:
What we now recognize as a bacterial infection (usually streptococcal) of the uterus or genital tract of women after childbirth, puerperal fever or childbed fever in the 18th and 19th centuries affected, on average, 6 to 9 women in every 1000 deliveries, killing 2 to 3 of them with peritonitis or septicemia. During times of epidemics, many more suffered and died. It was the single most common cause of maternal mortality, accounting for about half of all deaths related to childbirth, and was second only to tuberculosis in killing women of childbearing age.
From the World Health Organization:
*In the 19th century the notorious childbed fever took many victims. Today puerperal infections are still a major cause of maternal mortality in developing countries and, to a lesser degree, in developed countries…
One of the most dangerous causative agents of puerperal sepsis and the concomitant maternal mortality is the Group A Streptococcus (GAS) or Streptococcus pyogenes. It was the main cause of childbed fever in Europe in the 19th century. Since then the virulence of GAS seems to have diminished, but in recent years a new period of increased virulence has arrived (Gaworzewska & Colman 1988, Swingler et al 1988). Concurrently a new syndrome was introduced, the Streptococcal Toxic Shock Syndrome (Strep TSS), caused by endotoxin producing GAS (Hoge et al 1993).*
And, in case you were wondering, WHO states that the most common cause of maternal mortality today is post-partum hemorrhage.