Una destinatio, viae diversae: Does exposure to the vaginal microbiota confer health benefits to the infant, and does lack of exposure confer disease risk?

Abstract

There are two ways by which a baby can come into this world: vaginally or by Cesarean delivery. Although the developmental paths that result in either vaginal or Cesarean birth a.re highly diverse and very similar at the same time, the actual indication of whether a pregnant woman has to undergo surgery is usually clear. In most cases, Cesarean deliveries are performed for obstetric, fetal, or maternal indications, some of which are considered absolute. For example, if the placenta or its vessels obscure the cervix (complete placenta previa or vasa previa, respectively), vaginal delivery would be lethal to the mother and/or her newborn. What is less clear, however, is the child's developmental path after delivery. In particular, there is much debate on whether Cesarean delivery increases the risk of several diseases later in life, and whether any of these diseases result from a lack of exposure to the mother's vaginal microbiota during birth. Cesarean delivery is the most common abdominal surgery in the USA, accounting for more than 1 million operations annually. Four decades ago, 1 in 20 births occurred via Cesarean, now it is 1 in 3 to 1 in 4. The appropriate rate of Cesarean delivery is not easily determined, since it depends not only on multiple maternal, fetal, and obstetrical comorbidities and risk factors, but also on whether the mother had a Cesarean delivery before. The relative safety of Cesarean delivery—if performed by a competent obstetrical surgeon in a hospital—is recognized by patients and their providers alike, and the attributable risk of morbidity and mortality for both mother and child is extremely low. However, Cesarean delivery as a procedure has come under increasing scrutiny in recent years, in part owing to its real or perceived risk of future …