(722) Admission cardiotocography in low-risk pregnancies and neonatal outcomes, the significance of undetected small-for-gestational age fetuses

To assess the association between undetected small-for-gestational age (SGA) fetuses and abnormal admission cardiotocograph (admCTG) in a low-risk population. To elucidate the risk for neonatal and obstetric distress in this group – undetected SGA fetuses with abnormal admCTG compared to non-SGA fetuses with normal admCTG.

Study Design:

A population-based cohort study including singleton pregnancies from the Stockholm-Gotland Obstetric cohort, Sweden, between February 1st 2012 and June 15th 2020. Elective cesarean deliveries, induction of labor, non-vertex presentation, and preterm births ( < 34 weeks) were excluded. Pregnancies were designated as high- or low-risk at time of admission to labor ward, based on pre-defined risk measures (e.g. maternal morbidity, pregnancy complications, identified fetal growth restriction). SGA was defined as birthweight < 10th percentile and < 3rd percentile for gestational age. Outcomes for neonates born < 6 hours after admission were assessed regarding composite severe neonatal outcome (Apgar < 4 at 5 min, HIE grade 2-3, neonatal seizures, neonatal death) as main outcome. Composite moderate neonatal outcome was defined as Apgar < 7 at 5 min, ua-pH < 7.0, ua-pH < 7.05 and BD ≥ 12 mmol/L, advanced neonatal resuscitation.

Results:

We included 127 461 women assessed as low risk at admission to labor ward. The incidence of abnormal admCTG was 4.9%. The proportion of SGA was higher in the abnormal admCTG group compared to the normal, SGA 10th percentile, 18.6% vs 9.7% (OR 2.1, 95% CI 1.9-2.3), SGA 3rd percentile, 6.5% vs 2.2% (OR 3.1, 95% CI 2.7-3.5). The risk of composites severe and moderate adverse neonatal outcome was higher among neonates with abnormal admCTG born SGA (10th percentile) compared to normal admCTG, non-SGA; 1.2% vs 0.05%, OR 28.2 (95% CI 11.9-66.5) and 6.6% vs 1.0%, OR 6.5 (95% CI 4.6-9.3), respectively.

Conclusion:

In this low-risk population, where known FGR were excluded, there was a non-negligible group of undetected SGA fetuses, who were more prone to present with abnormal admCTG with substantially higher risk of severe and moderate neonatal outcome.