The impact of pre-pregnancy body mass index and maternal diseases on the offspring outcomes in preterm infants < 32 weeks: five-year retrospective mediation analysis

Abstract Introduction Different pre-pregnancy body mass index (BMI) may lead to adverse pregnancy complications and unfavorable outcomes, but few studies focus on preterm infants under 32 gestational weeks. The associated mediation mechanisms have not been fully evaluated. This study investigated the association between BMI, pregnancy-associated diseases and offspring outcomes in preterm infants born before 32 gestational weeks, as well as analyzed the mediating role played by pregnancy-associated diseases in this context. Methods A retrospective study involving 1466 preterm infants born before 32 gestational weeks (2017–2023) was conducted. Multivariate regression was utilized to analyze correlations between pre-pregnancy BMI categories, pregnancy-associated diseases, and offspring outcomes. Furthermore, a parallel mediation analysis (“lavaan” package in R software) along with a bootstrap test, was conducted to assess the direct/indirect effects. Results The high-BMI subgroup showed a notably higher prevalence of preeclampsia (OR = 3.273, 95% CI: 2.426–4.436) and gestational diabetes mellitus (GDM) (OR = 1.573, 95% CI: 1.223–2.022), along with lower gestational age and 1-min Apgar score in their preterm infants (P < 0.05). No statistical differences occurred in incidence of long-term complications (P > 0.05). The low-BMI subgroup had a reduced prevalence of GDM (P < 0.05). However, no statistical differences were found in its impact on offspring outcomes and complications (P > 0.05). Further exploration of the mediating effect revealed that both preeclampsia and GDM played a partial mediating role in the association between high BMI and gestational age, as well as between high BMI and 1-min Apgar score. Notably, preeclampsia had a relatively stronger mediating effect than GDM on the variance in gestational age (Indirect effect=-0.049 (-0.090, -0.008)) and 1-min Apgar score (Indirect effect=-0.078 (-0.139, -0.017)), accounted for 20.4% and 17.4% of the total effect, respectively. Conclusion High maternal BMI partially reduced gestational age and 1-min Apgar score in patient with preeclampsia and GDM in preterm infants < 32 weeks. During the window of pre-pregnancy healthcare intervention, promoting weight management strategies could effectively reduce the incidence of GDM and preeclampsia, thereby mitigating adverse outcomes.