The subject of this 2017 Spanish review was human placental epigenetic changes:

“39 papers assessing human placental epigenetic signatures in association with either

• (i) psychosocial stress,
• (ii) maternal psychopathology,
• (iii) maternal smoking during pregnancy, and
• (iv) exposure to environmental pollutants,

were identified.

Their findings revealed placental tissue as a unique source of epigenetic variability that does not correlate with epigenetic patterns observed in maternal or newborn blood.“

Each study’s confounders were summarized by a column in Table 1. Some of the reviewers’ comments included:

“33 out of 39 papers reviewed (85%) reported significant associations between either placental DNA methylation or placental miRNA expression and exposure to any of the risk factors assessed. However, the methodological heterogeneity present throughout the studies reviewed does not allow meta-analytic exploration of reported findings.

Heterogeneity regarding the origin of biological tissues analyzed confounds the replicability and validity of reported findings and their potential synthesis.”

Sponsors and researchers really have to take their work seriously if the developmental origins of health and disease hypothesis can advance to a well-evidenced theory. Study designers should:

1. Sample consequential dimensions. “There were no studies examining histone modifications.” Why were there no human studies in this important category of epigenetic changes in the placenta, the “barrier protecting the fetus“?
2. Correct methodological deficiencies in advance. Eliminate insufficiencies like “Once collected, processing and storage of placental samples also differed across studies and was not reported in all of them.”
3. Stop using convenient but non-etiologic proxy assays such as global methylation. How can a study advance the DOHaD hypothesis if everyone knows ahead of time that its outcome will be yet another finding that epigenetic changes “are associated with” non-causal factors?
4. Forget about non-biological measurements like educational attainment per Does a societal mandate cause DNA methylation?.

Every human alive today has observable lasting epigenetic effects caused by environmental factors during the earliest parts of our lives, and potentially even before we’re conceived. Isn’t this sufficient rationale to expect serious efforts by research sponsors and designers?

https://www.sciencedirect.com/science/article/pii/S0892036217301769 “The impact of prenatal insults on the human placental epigenome: A systematic review” (click the Download PDF link to read the paper)