Fetal growth restriction and other risk factors for stillbirth in a New Zealand setting

Background: Stillbirth affects almost 1% of pregnant women in the Western world but is still not a research priority. Aims: To assess in a cohort of stillbirths: the demographic risk factors, the prevalence of small for gestational age (SGA) by customised and population centiles, and the classification of death using the Perinatal Society of Australia and New Zealand Perinatal Death Classification (PSANZ‐PDC). Methods: The study population comprised 437 stillborn babies (born from 1993 to 2000 at National Women's Hospital, Auckland, New Zealand) and their mothers. The referent population for demographic factors was live births n = 69 173. Results: After multivariable analysis, risk factors for stillbirths were: Indian (odds ratio (OR) 1.85, 95%CI (1.18, 2.91)), or Pacific Islander (OR 1.65, 95%CI (1.27, 2.14)); smoking (OR 1.33, 95%CI (0.99, 1.79)) or unknown smoking status (OR 2.87, 95%CI (2.30, 3.58)); nulliparity (OR 1.42, 95%CI (1.10, 1.83)), and para 2 (OR 1.36, 95%CI (1.01, 1.83)). One hundred and twenty‐nine (46%) stillbirths born ≥ 24 weeks (n = 278) were SGA by customised, and 94 (34%) by population centiles. Customised SGA was more common in preterm versus term stillbirths (101 of 198 (51%) vs 28 of 80 (35%), respectively, P = 0.02) but rates of population SGA did not differ (72 of 198 (36%) vs 22 of 80 (28%) P = 0.16). ‘Spontaneous preterm’ was the most common cause of stillbirth at < 28 weeks and ‘unexplained’ at ≥ 28 weeks using PSANZ‐PDC classification. Conclusions: This study again emphasises the importance of suboptimal fetal growth as an important risk factor for stillbirth. Customised centiles identified more stillborn babies as SGA than population centiles especially preterm.