Elucidating the role of maternal environmental exposures on offspring health and disease using two-sample Mendelian randomization

BACKGROUND

There is considerable interest in estimating the causal effect of a range of maternal environmental exposures on offspring health-related outcomes. Previous attempts to do this using Mendelian randomization methodologies have been hampered by the paucity of epidemiological cohorts with large numbers of genotyped mother-offspring pairs.

METHODS

We describe a new statistical model that we have created which can be used to estimate the effect of maternal genotypes on offspring outcomes conditional on offspring genotype, using both individual-level and summary-results data, even when the extent of sample overlap is unknown.

RESULTS

We describe how the estimates obtained from our method can subsequently be used in large-scale two-sample Mendelian randomization studies to investigate the causal effect of maternal environmental exposures on offspring outcomes. This includes studies that aim to assess the causal effect of in utero exposures related to fetal growth restriction on future risk of disease in offspring. We illustrate our framework using examples related to offspring birthweight and cardiometabolic disease, although the general principles we espouse are relevant for many other offspring phenotypes.

CONCLUSIONS

We advocate for the establishment of large-scale international genetics consortia that are focused on the identification of maternal genetic effects and committed to the public sharing of genome-wide summary-results data from such efforts. This information will facilitate the application of powerful two-sample Mendelian randomization studies of maternal exposures and offspring outcomes.

Placental and fetal effects of antenatal exposure to antidepressants or untreated maternal depression

OBJECTIVE

To assess systematically the effects of antidepressants and untreated maternal depression on human placenta and the developing fetus.

METHODS

Pertinent medical literature information was identified using MEDLINE/PubMed, SCOPUS and EMBASE. Electronic searches, limited to human studies published in English, provided 21 studies reporting primary data on placental and fetal effects of antidepressant exposure or untreated gestational depression.

RESULTS

The impact of antidepressants and non-medicated maternal depression on placental functioning and fetal biochemical architecture seems to be demonstrated, although its clinical significance remains unclear. More robust data seem to indicate that exposure to either antidepressants or untreated maternal depression may induce epigenetic changes and interfere with the physiological fetal behavior. Two cases of iatrogenic fetal tachyarrhythmia have also been reported.

CONCLUSIONS

Future research should clarify the clinical relevance of the impact of antidepressant and untreated maternal depression exposure on placental functioning. Moreover, ultrasound studies investigating fetal responses to antidepressants or maternal depressive symptoms are mandatory. This assessment should be performed during the whole duration of gestational period, when different fetal behavioral patterns become progressively detectable. Analyses of biochemical and epigenetic modifications associated with maternal mood symptoms and antidepressant treatment should also be implemented.

A statistical framework for testing the causal effects of fetal drive

Maternal genetic and phenotypic characteristics (e.g., metabolic and behavioral) affect both the intrauterine milieu and lifelong health trajectories of their fetuses. Yet at the same time, fetal genotype may affect processes that alter pre and postnatal maternal physiology, and the subsequent health of both fetus and mother. We refer to these latter effects as 'fetal drive.' If fetal genotype is driving physiologic, metabolic, and behavioral phenotypic changes in the mother, there is a possibility of differential effects with different fetal genomes inducing different long-term effects on both maternal and fetal health, mediated through intrauterine environment. This proposed mechanistic path remains largely unexamined and untested. In this study, we offer a statistical method to rigorously test this hypothesis and make causal inferences in humans by relying on the (conditional) randomization inherent in the process of meiosis. For illustration, we apply this method to a dataset from the Framingham Heart Study.

Increasing use of atypical antipsychotics and anticonvulsants during pregnancy

PURPOSE

To quantify maternal use of atypical antipsychotics, typical antipsychotics, anticonvulsants, and lithium during pregnancy.

METHODS

Tennessee birth and death records were linked to Tennessee Medicaid data to conduct a retrospective cohort study of 296,817 women enrolled in Tennessee Medicaid throughout pregnancy who had a live birth or fetal death from 1985 to 2005.

RESULTS

During the study time period, the adjusted rate of use of any study medication during pregnancy increased from nearly 14 to 31 per 1000 pregnancies (β = 0.08, 95% CI = 0.07, 0.09). Significant increases were reported in use of anticonvulsants alone among mothers with pain and other psychiatric disorders, atypical antipsychotics alone among mothers with bipolar disorders, schizophrenia, unipolar depressive disorders, and other psychiatric disorders, and more than one studied medication for mothers with epilepsy, pain disorders, bipolar disorders, unipolar depressive disorders, and other psychiatric disorders. Significant decreases were reported in use of lithium alone and typical antipsychotics alone for all clinically meaningful diagnosis groups.

CONCLUSIONS

There was a substantial increase in use of atypical antipsychotics alone, anticonvulsants alone, and medications from multiple studied categories among Tennessee Medicaid-insured pregnant women during the study period. Further examination of the maternal and fetal consequences of exposure to these medications during pregnancy is warranted.