Cardiotocographic parameters in small-for-gestational-age fetuses: How do they vary from normal at different gestational ages? A study of 11687 fetuses from 25 to 40 weeks of pregnancy.

AIM: The aim of this study was to assess how cardiotocographic (CTG) parameters differ between small-for-gestational-age (SGA) and normal fetuses at different gestational ages.

METHODS: This was a retrospective cross-sectional study using the first antepartum tracing of singleton pregnancies with no malformations. Fetuses with birthweight ≥10th percentile for gestational age and other normal pregnancy outcome criteria (term birth, normal umbilical artery pH and Apgar scores, no intensive care unit admission) were compared with fetuses with birthweight <10th and <3rd percentiles for gestational age (SGA < p10 and SGA < p3, a subgroup of the latter). Each CTG parameter was compared, by gestational age, using both statistical tests and percentile curves derived from normal outcome cases. Tracings were analyzed with the OmniviewSisPorto® 3.7 system.

RESULTS: A total of 11 687 tracings (from the same number of fetuses) were analyzed: 9701 normal, 1986 SGA < p10, and 543 SGA < p3. SGA fetuses had lower long- and short-term variability, and number of accelerations, with more pronounced differences between around 28 and 35 weeks. In contrast, baseline was lower in SGA fetuses from 34 weeks onwards. All differences were more pronounced for SGA < p3 fetuses. Similar trends throughout gestation occurred in all groups: decrease in baseline, and increase in long- and short-term variability, and accelerations.

CONCLUSIONS: This study represents an important step for accurate CTG interpretation in SGA fetuses and, consequently, management of fetal growth restriction (FGR), as it contributes to differentiate between maturational CTG changes that occur physiologically throughout pregnancy, and possible signs of fetal compromise in FGR.