Canada: Obese pregnancies pose a higher risk of perinatal death that may be mediated by a lower gestational age at delivery, concludes a recent study in the journal PLOS One.
The pathophysiology behind the link between obesity and perinatal death is not fully understood and is thought to be due to higher rates of pregnancy complications at earlier gestation amongst obese women. Jeffrey N. Bone, University of British Columbia and the Children's and Women's Hospital and Health Centre of British Columbia, Vancouver, BC, Canada, and colleagues, therefore, aimed to quantify the proportion of perinatal deaths amongst obese and overweight women mediated by gestational age at stillbirth or live birth.

All singleton births at ≥20 weeks' gestation in British Columbia, 2004–2017 were included, and pregnancy terminations were excluded. Using natural effects models with adjustment for potential confounders, the researchers estimated the proportion of the association between BMI and perinatal death mediated by gestational age at delivery (in weeks). Sensitivity analyses for unmeasured confounding and women missing BMI were conducted.
The researchers reported the following findings:
Of 392,820 included women, 20.6% were overweight and 12.8% obese.
· Women with higher BMI had a lower gestational age at delivery. Perinatal mortality was 0.5% (1834 pregnancies); and was elevated in overweight (adjusted odds ratio [AOR] = 1.22) and obese women (AOR = 1.55).
· Mediation analysis showed that 63.1% of the association between obesity and perinatal death was mediated by gestational age at delivery (natural indirect effect AOR = 1.32, natural direct effect AOR = 1.18). Similar, but smaller effects were seen when comparing overweight women vs. women with a normal BMI.
· Estimated effects were not affected by adjustment for additional risk factors for perinatal death or sensitivity analyses for missing data.

To conclude, women with pre-pregnancy obesity are at a higher risk of perinatal mortality. Results from mediation analysis suggest that earlier gestational age at delivery may be implicated in many of these obesity-related perinatal deaths.
Based on the results, the researchers suggest that "timely obstetric intervention combined with access to neonatal intensive care earlier in gestation may reduce the risk of neonatal death among infants in these women."
"To better inform the pregnancy management among obese women further studies will be required to disentangle the causal pathways under which obesity increases the risk of perinatal death, including, for example, gestational diabetes and other obesity-related pregnancy complications."
Reference:
Bone JN, Joseph KS, Mayer C, Platt R, Lisonkova S (2022) The association between pre-pregnancy body mass index and perinatal death and the role of gestational age at delivery. PLoS ONE 17(3): e0264565. https://doi.org/10.1371/journal.pone.0264565
KEYWORDS: Plos One, obesity, perinatal death, pregnancy, BMI, gestational age, body mass index, women, obese women, gestation, Jeffrey N Bone, delivery, pregnancy complications, overweight