The MFMU VBAC Success Calculator: statistical prediction and race in an ethnography of obstetric thinking
Skip to main content
Open Access Publications from the University of California


UC San Francisco Electronic Theses and Dissertations bannerUCSF

The MFMU VBAC Success Calculator: statistical prediction and race in an ethnography of obstetric thinking


In 2015 some 29.7 million women gave birth via cesarean, the majority of whom will subsequently give birth via repeat cesareans. The steep rise in surgical births might outpace the abilities of health systems to safely conduct the surgery, potentially reversing hard fought gains in reducing maternal mortality in low- and middle-income countries. The United States too has witnessed a sharp increase in cesarean use over the last 20 years, now accounting for 1 in 3 births, or 1.2 million per year. Even in California, the state that leads the nation in reducing avoidable maternal morbidity and mortality, 40% of the rise in maternal morbidity over the last 20 years can be explained by cesarean overuse, with Black women most seriously affected. After decades of advocating for universal facility-based childbirth, the global health community must now deal with the consequences of a sometimes necessary but often overused surgery. The U.S. cesarean rate is sustained by increases in primary cesareans and decreases in the number of women attempting a Vaginal Birth After Cesarean (VBAC). Down from a peak of 28% in the late 1990s, the VBAC rate is persistently low at 13%. After a first cesarean, most women in the U.S. continue to schedule an Elective Repeat Cesarean Delivery (ERCD). In a 2010 consensus statement the NIH found that several prediction models could accurately predict VBAC using varying combinations of individual risk factors. The rationale for the development of accurate VBAC prediction tools was to support clinicians in identifying those candidates with the highest chance for a successful VBAC. The VBAC rate might increase if only those candidates assessed to have the highest chance for success went on to attempt VBACs, on the assumption that a proportion of these women currently underwent repeat cesareans. One VBAC prediction tool rose to prominence in the United States: the Maternal-Fetal Medicine Units (MFMU) VBAC Success Calculator. The VBAC calculator predicted the probability for a successful VBAC by combining the indication for the prior cesarean with a woman’s age, Body Mass Index (BMI), and her race or ethnicity, categorized as White, Black, or Hispanic. All these factors were known at the first prenatal visit, allowing clinicians and women to make an early plan for the ultimate mode of birth. On average the VBAC calculator gave scores to Black and Hispanic women that were 5-15 points lower than White women with similar risk factors. The MFMU VBAC calculator was invented and widely disseminated without seeking input from those who were thought to most benefit from the tool, namely pregnant women and birthing individuals who have had a prior cesarean. The aims of this dissertation were two-fold. First, I critically evaluated the invention of the VBAC calculator, paying attention to scientific paths not taken and to the ways in which practices that sustained the calculator silenced alternative approaches to the uncertainty of planning a VBAC. Second, I assessed the impact of the VBAC calculator on the pregnancy and birth experiences of a diverse group of women with varying birth histories and racial/ethnic identifications. The methodological approach for the study was critical and ethnographic, including an 18-month immersion in scientific papers, blog posts, podcasts, visual artifacts, interviews, audio recordings of prenatal visits, and observations. In order to obtain the full range of engagements with this technology, I purposively selected 22 key informants as users and non-users of the calculator based on their research publications or public statements. In order to understand the practical applications of the calculator, I interviewed 17 providers (perinatologists, general obstetrician-gynecologists, and Certified Nurse Midwives or CNMs) who worked across 4 different institutions. I enrolled 27 pregnant and 4 postpartum women who spoke Spanish or English, were over 18-years old, and had at least one prior cesarean. Women had diverse birth histories and racial/ethnic identifications, whose calculated likelihood of successful VBAC ranged from 12% to 95%. Ultimately, 13 women went on to have VBACs, 10 had unplanned cesareans, and 8 had ERCDs. Qualitative data were analyzed thematically on multiple levels, using modified grounded theory. In Chapter 1, I argue that the VBAC calculator marginalized the diverse ways in which VBAC candidates approached risk and uncertainty. I present evidence from VBAC candidates whose experiences run counter to the calculator, including women who saw their pregnancies as an embodied and unfolding process rather than as a pre-ordained statistical fact. In Chapter 2, I directly address the racial dimensions and consequences of the calculator. I argue that the VBAC calculator automated the reproduction of racism by foreclosing the possibility that racism, not race, explained the differences in successful VBAC rates between White, Black, and Hispanic women. In Chapter 3, I examine how non-numeric elements influence the decision to attempt a VBAC or a repeat cesarean. That VBAC prediction models appear to be a globally ascendant approach to counseling should concern Global Health scholars. Under conditions of cesarean overuse, which is rapidly becoming most of the world, VBAC prediction models turn more prior cesareans into recurring indications, thus challenging Global Health efforts to safely reduce cesarean use. To date, the Global Health discussions around mistreatment of women in birth facilities has largely focused on measuring and describing experiences of mistreatment, violence, and abuse. In the mistreatment research literature, violations of autonomy are among the most common, and many recommend that women worldwide transition into the decision making role in order to fulfill their fundamental right to self-determination in childbirth. However, due to the ways that the VBAC calculator both engaged women as decision makers and reproduced racism in the process, the VBAC calculator complicates the notion that mistreatment, violence, and abuse during childbirth is adequately addressed through the concept of choice.

Main Content
For improved accessibility of PDF content, download the file to your device.
Current View