Eclampsia: is there a seasonal variation in incidence?

The Association Between Season and Hypertensive Disorders in Pregnancy: a Systematic Review and Meta-analysis

There is increasing and inconsistent evidence of a relationship between hypertensive disorders in pregnancy (HDPs) and season of delivery or conception. In this systematic review and meta-analysis, we assessed the association between season and HDPs. The review protocol was registered in PROSPERO (CRD42021285539). Four databases, the Cochrane Library, PubMed, EMBASE, and Web of Science, were searched until September 29th, 2021. Two authors extracted data independently and used the Newcastle-Ottawa quality assessment scale (NOS) to evaluate study quality. A random effects model and the Mantel-Haenszel method were used to calculate pooled Odds ratios (ORs) and 95% confidence intervals (95% CIs). Subgroup analyses and sensitivity analyses were performed to find the source of heterogeneity and Begg's funnel plot and Egger's test were used to check for the risk of publication bias. Finally, twenty articles were included in the systematic review, and 11 articles were included in the meta-analysis. The quantitative analysis of the association between delivery season and HDPs showed that the odds of HDPs was higher in women who delivered in winter than in those who delivered in summer (OR = 1.18, 95% CI 1.02-1.38, P < 0.001) and all other seasons (OR = 1.17, 95% CI 1.03-1.34, P < 0.001). In the qualitative analysis of the association between conception season and HDPs, four of seven studies suggested that women who conceived in summer had a higher risk of HDPs than those who conceived in other seasons. Based on the evidence to date, we found weakly positive relationships between HDPs and summer conception and winter delivery.

Associations of meteorology with adverse pregnancy outcomes: a systematic review of preeclampsia, preterm birth and birth weight

The relationships between meteorology and pregnancy outcomes are not well known. This article reviews available evidence on the relationships between seasonality or meteorology and three major pregnancy outcomes: the hypertensive disorders of pregnancy (including preeclampsia, eclampsia and gestational hypertension), gestational length and birth weight. In total 35, 28 and 27 studies were identified for each of these outcomes. The risks of preeclampsia appear higher for women with conception during the warmest months, and delivery in the coldest months of the year. Delivery in the coldest months is also associated with a higher eclampsia risk. Patterns of decreased gestational lengths have been observed for births in winter, as well as summer months. Most analytical studies also report decreases in gestational lengths associated with heat. Birth weights are lower for deliveries occurring in winter and in summer months. Only a limited number of studies have investigated the effects of barometric pressure on gestational length or the effects of temperature and sunshine exposure on birth weight, but these questions appear worth investigating further. Available results should encourage further etiological research aiming at enhancing our understanding of the relationships between meteorology and adverse pregnancy outcomes, ideally via harmonized multicentric studies.