Prospective risk of stillbirth according to fetal size at te
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Fetal size at term is a major determinant of the risk of stillbirth, and one of the key considerations for clinicians regarding their advice to mothers about the best time to deliver the baby. The author wanted to investigate the predictive value of different small for gestational age (SGA) bands and the effect of conservative management on the prospective risk of stillbirth.

The study cohort consisted of an anonymised database of 1,120,758 term deliveries in the GAP program 2015–19, including 2,460 stillbirths. Gestational age of stillbirth was adjusted for death to delivery interval. Prospective stillbirth risk was defined as fetal deaths in the current week divided by total undelivered pregnancies (e.g. prospective risk at week 37 = deaths in week 37 / total births 37–41+ weeks * 1000). The data were analysed in bands determined by customized centiles: less than 3, 3 less than 10, and 10 less than90. Risk ratios were calculated using the 10<90 centile band at 37 weeks as reference.

The baseline prospective stillbirth risk (10<90 centile at 37 weeks; per 1000) was 0.27 and rose to 1.39 at 41+ weeks. In comparison, risk in the 3 less than 10 centile band rose from 0.64 to 2.42, and in fetuses less than 3 centiles from 1.79 to 6.84 (table 1). The table also shows the risk ratios for waiting additional weeks at term for each of the centile categories.

SGA fetuses have an increasing risk of fetal death at term which is related to the degree of smallness. The information provided, together with other considerations and results of investigations where available, will help clinicians to determine the advice to give to mothers about their baby's risk of stillbirth and help plan management and timing of delivery.