Design: Systematic review and meta-analysis of 17 randomised trials with usual-care or no-intervention controls
Population: Pregnant and postpartum women; prevention-oriented and symptomatic populations analysed separately
Primary outcome: Depressive and anxiety symptom scores, antenatal and postpartum
Effect: Antenatal depressive symptoms SMD -0.52 (95% CI -0.75 to -0.30), I-squared 46%; antenatal anxiety SMD -0.03 (-0.31 to 0.25)

Advice to stay active in pregnancy is universal and usually vague. This meta-analysis isolates what standalone physical activity does to perinatal mood by including only trials in which the control arm received usual care or nothing — no education package, no added counselling — so the exercise is doing the work. Seventeen randomised trials were included from 10,938 records screened.

In prevention-oriented trials — women not selected for symptoms at baseline — physical activity was associated with lower antenatal depressive symptom scores (SMD -0.52, 95% CI -0.75 to -0.30, I-squared 46%, seven trials), and with lower postpartum scores (SMD -0.33, -0.57 to -0.09), though the postpartum pool was severely heterogeneous at I-squared 86%. In a separate exploratory analysis of women who were already symptomatic, postpartum depressive scores were also lower (SMD -0.38, -0.72 to -0.04). Antenatal anxiety showed nothing (SMD -0.03, -0.31 to 0.25, I-squared 0%, three trials). Certainty was low to very low throughout. Secondary analyses favoured structured programmes of about an hour, three times a week.

The change this should make is small and concrete. Stop saying 'try to stay active' and instead prescribe what the trials actually delivered: structured, supervised where possible, three sessions a week of about 60 minutes, started antenatally and continued after birth. Say plainly that it is for mood as well as for weight and glycaemia — women adhere better to an intervention whose purpose they have been told. And do not offer it for anxiety, where the pooled estimate is flatly null with no heterogeneity to hide behind.

Write the prescription: three sessions weekly, about 60 minutes, structured rather than 'more walking'.
State the mood indication explicitly when you give it.
Screen with EPDS antenatally and again postpartum regardless — this is not a substitute for detection.
Do not extend the claim to anxiety; the antenatal anxiety estimate was null.
Check for obstetric contraindications before recommending a structured programme.

Why it matters

It converts a piece of generic antenatal advice into a specific prescription with a dose.

The statistics, in plain English

An SMD of -0.52 is a moderate effect on symptom scores, roughly half a standard deviation. It is not a reduction in diagnosed depression, which these trials were not designed or sized to measure. The postpartum estimate carries I-squared of 86%, meaning the trials disagree with each other so much that the pooled number describes no single programme well — treat it as a direction, not a magnitude. The antenatal anxiety result is the opposite case: a confidence interval straddling zero with I-squared of 0% is consistent agreement on no effect, which is more informative than a wide interval would be.