12. Emily Oster, PhD: Breastfeeding Recommendations, Rising C-section Rates, and Other Controversies

In this interview, Mitch Belkin and Daniel Belkin speak with Brown Economics Professor Emily Oster about the studies behind breastfeeding recommendations, the dramatic increase in the U.S. C-section delivery rate over the last half century, and how she approaches analyzing studies. 

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Who is Emily Oster?

Emily Oster is the Royce Family Professor of Teaching Excellence and Professor of Economics at Brown University where she studies health, behavioral, and development economics. She received her PhD from Harvard University and taught at the University of Chicago Booth School of Business. She is the author of three popular books on pregnancy and parenting: Expecting Better, Cribsheet, and The Family Firm. 

What topics do we cover in this episode?

This interview focuses on two major topics: breastfeeding and the C-section rate, which are best covered in Cribsheet and Expecting Better, respectively.

Breastfeeding

What are the official recommendations on breastfeeding?

The CDC and the American Academy of Pediatrics recommend exclusive breastfeeding for 6 months and then continued breastfeeding while introducing food until 12 months of age or older. The benefits of breastfeeding are said to include: decreased risk of asthma; decreased ear, respiratory, and gastrointestinal infections; lower rates of obesity and type 1 diabetes. Some also claim that breastfeeding can lead to increased infant IQ and higher wages in adulthood, among many other purported benefits. For mothers, the benefits of breastfeeding are said to include decreased risk of ovarian cancer, breast cancer, type 2 diabetes, and hypertension.

What does Professor Emily Oster think about breastfeeding?

Professor Oster argues that at least some of these claims are overblown or based on relatively weak evidence. In large part, this is because most of the claims come from observational and case-control studies, which do not allow one to draw causal conclusions. As Professor Oster reiterates in this podcast, women in the developed world who choose to breastfeed differ from women who choose not to breastfeed in significant ways. For example, they tend to be wealthier and more educated. These demographic factors are already correlated with better infant outcomes independent of whether women choose to breastfeed or not.

Do any large breastfeeding RCTs exist?

Yes, the PROBIT study (AKA the Promotion of Breastfeeding Intervention Trial) is a Randomized Controlled Trial in Belarus conducted in the 1990s that took 17,046 healthy mother-infant pairs of full-term singleton infants and randomly assigned them to either an intervention arm that encouraged breastfeeding or a control group that had the usual infant feeding recommendations.

What were the results of the PROBIT study?

At 12 months, infants from the intervention group were about twice as likely to be breastfed compared to the control group (19.7% vs 11.4%). This demonstrates that the encouragement intervention was effective in promoting breastfeeding. At 3 months, the intervention group was six times more likely to be exclusively breastfed (43.3% vs 6.4%; P<.001). The intervention group also had a significant reduction in the risk of 1 or more gastrointestinal tract infections (9.1% vs 13.2%) and of atopic eczema (3.3% vs 6.3%). However, there was no significant reduction in respiratory tract infection.

Cesarean sections

Where does the name Cesarean section come from?

There are numerous explanations of where the word came from. One apocryphal story is that Julius Caesar was actually born by C-section, which is almost certainly untrue given that his mother survived long after childbirth. There are also many other etymological explanations for the name, including the root of the word coming from a similar root as the Latin word for “to cut” (caedere).

Why are C-sections performed?

C-sections are a surgical procedure used to deliver a baby through an incision in the abdomen and uterus. They are usually performed when a vaginal delivery presents increased risks for baby and/or mom. Medical reasons for the surgery include prolonged or abnormal labor, twin pregnancy, pre-eclampsia, breech birth, fetal distress, and problems with the placenta or umbilical cord.

The rise in C-sections:

In 1970, 5% of U.S. births were by Caesarean section. In 2019, the CDC’s official C-section rate was 31.7%.  This 6-fold increase could be due to a number of factors, which we discuss in this episode. Though we do not discuss it in great detail, the WHO has a so-called “ideal C-section rate” which is between 10-15%. This ideal rate stems from the following argument: as caesarean sections rise towards 10% in a given population, the number of maternal and newborn deaths decreases. However, when the rate is greater than 10%, there is no evidence of improvements in mortality. Some possible explanations for the increase in the U.S. C-section rate include:

1. An increase in the number of high risk pregnancies due to increases in obesity, diabetes, pre-eclampsia, hypertension, and maternal age.
2. Increased litigation (or fear of litigation). For example, malpractice premiums are positively correlated with higher rates of C-sections.
3. The advent and increasing use of continuous fetal heart rate monitors, which have been demonstrated to increase the rate of c-sections. 
4. Increased patient preference for c-sections.
5. Attending preference. Studies show an increased number of C-sections just prior to the end of shifts and before lunch time.
6. Insufficient training with breech births leading physicians to opt for c-sections in circumstances that previously would have been delivered vaginally.
7. Higher physician and/or hospital compensation for c-sections as compared to vaginal births may lead hospitals to incentivize performing more c-sections.

Please note this is not a complete list of the possible reasons for the increased C-section rate.

Miscellaneous:

In our podcast, we reference the following papers, ideas, and talks:

• The 2007 TED Talk on AIDS in Africa by Professor Emily Oster
• A paper in which Professor Oster argues that the the increased ratio of men to women in Asia could be explained in part by Hepatitis B infection (2005)
• Another paper in which she retracts the claims of her previous paper (Hepatitis B Does Not Explain Male-Biased Sex Ratios in China) (2008)
• The Term Breech Trial – Lancet (2000)
• Door-to-Balloon time
• Amy Finkelstein paper on Source of Geographic Variation in Healthcare spending: evidence from patient migration
• Judith Rich Harris Argument – The Nurture Assumption
• Professor Emily Oster’s Parent Data Substack

Errata:

1. In the introduction, we accidentally say Academy of Pediatrics at one point when we meant to say American Academy of Pediatrics.
2. In the introduction, we state that one reason for C-section delivery is “protracted vaginal delivery”. We meant to say “protracted labor” defined as the arrest of cervical dilation prior to vaginal delivery.