The uk equivalent report is much more nuanced - note the use of "might have made a difference" vs "preventable":
"Mental health remains one of the leading causes of maternal death in pregnancy and the first postnatal year. Many of the women who died from suicide or substance misuse faced multiple adversity. Assessors felt that improvements in care might have made a difference in outcome for 67% of women who died by suicide, 29% who died from substance misuse and 18% of those who died by homicide. This report emphasizes once again the importance of immediate risk management and the potential for rapid deterioration, particularly postnatally. These messages are equally important across pregnant women of all ages, especially those who have had a pregnancy loss event, but this report does show a need for special attention around mental health for pregnant teenagers."