In a Ghanaian pregnancy cohort, hotter pregnancies came with higher psychosocial stress

Most of what is known about heat and pregnancy concerns birth outcomes — preterm delivery, low birthweight, stillbirth. Much less is known about the mother's mental state during the pregnancy itself, and almost none of that evidence comes from sub-Saharan Africa, where the heat is greatest and the health systems thinnest. A paper in Environmental Research: Health addresses that gap directly [s1].

The cohort and the measurements

The analysis uses psychosocial stress scores and covariate data from the Ghana Randomized Air Pollution and Health Study (GRAPHS) [s1]. Stress was measured with the Crisis in Family Systems-Revised Life Events Questionnaire, which asks about life events rather than mood symptoms [s1].

Exposure was daily maximum and minimum shaded wet bulb globe temperature, linked to participants' stress scores [s1]. Wet bulb globe temperature is a heat-stress index rather than a thermometer reading: it combines air temperature with humidity and radiant heat, which is the combination the body actually has to cope with.

The authors used ordinal logistic regression on pregnancy-average and trimester-average exposures, plus distributed lag non-linear models to look at how associations varied across gestation [s1].

What was found

Higher average maximum wet bulb globe temperature across pregnancy was associated with increased odds of higher psychosocial stress. Each 1 degree C increase in maximum WBGT was associated with 64% higher odds of belonging to a higher stress category (OR 1.64; 95% CI 1.17–2.31; p = 0.0040) [s1].

In trimester-average models, higher first-trimester maximum WBGT was also associated with higher stress (OR 1.44; 95% CI 1.15–1.81; p = 0.0014) [s1].

The lag models suggested timing matters in a way the averages hide. Relatively cooler daily maximum WBGT values — at the 25th percentile — were associated with decreased odds of stress in early pregnancy, whereas extreme daily maximum values at the 99th percentile showed a pattern consistent with increased odds of stress in mid-to-late gestation [s1].

How much weight this can carry

An odds ratio of 1.64 per degree is large, and the confidence interval is wide — 1.17 to 2.31 — which is what a modest number of participants buys. This is a single cohort in a single country, and the exposure and the outcome are both measured against calendar time, so anything else that tracks the seasons in rural Ghana is a candidate explanation: agricultural work cycles, food availability, disease seasonality, income.

The stress instrument matters too. A life-events questionnaire captures reported crises, and heat plausibly affects both the occurrence of hardship and how a person answers questions about it. Neither channel is a nervous-system effect of temperature, and the study cannot separate them.

The authors' own framing is careful. They present the findings as highlighting gestational windows in which heat exposure may influence stress, and emphasise the need for further research into underlying mechanisms and effective interventions to protect maternal mental health in heat-vulnerable settings [s1]. Psychosocial stress is described as an established antecedent of perinatal depression [s1] — an antecedent, not the condition.

The wider evidence on heat and pregnancy

A systematic review and meta-analysis published on August 21 gives a sense of how the broader field is doing on the birth-outcome side, and of its limits [s2].

Searching five databases to June 2024, the authors ran a random-effects meta-regression to estimate heat thresholds for acute effects on adverse outcomes [s2]. Across 21 studies covering 5,589,862 participants, they identified maximum-temperature thresholds of 30.55 degrees C, 34.11 degrees C and 39.07 degrees C for 5%, 10% and 20% increases in risk respectively [s2].

The narrative synthesis was far larger — 103 studies covering 41,951,950 participants — and its main conclusion is a methodological one: the field uses heterogeneous indicators and lacks comprehensive heat stress indices [s2]. The review's authors also state its own limitations plainly, including no independent dual data extraction and quality assessment performed by a single person [s2].

That is the context in which the Ghana study's use of wet bulb globe temperature stands out. Studies that measure heat as air temperature alone are measuring something different from what the body experiences, and the review's finding that the literature lacks comprehensive heat stress indices [s2] is a direct statement of the problem.

What to watch

Whether the association replicates in another sub-Saharan cohort with an independent stress measure, and whether any trial tests an intervention — cooling, work rescheduling, antenatal mental health support — against a heat-exposure outcome. Threshold estimates are useful for warning systems only if something follows the warning.

Sources

• Heat exposure and maternal stress: evidence from the GRAPHS pregnancy cohort in Ghana — Environmental Research: Health, 2026-08-25
• A systematic review and meta-analysis on heat thresholds for maternal health and birth outcomes — Nature Communications, 2026-08-21