Longitudinal changes of cardiotocographic parameters throughout pregnancy: a prospective cohort study comparing small-for-gestational-age and normal fetuses from 24 to 40 weeks.

OBJECTIVE: To compare longitudinal trends of cardiotocographic (CTG) parameters between small-for-gestational-age (SGA) and normal fetuses, from 24 to 41 weeks of pregnancy.

METHODS: A prospective cohort study was carried out in singleton pregnancies without fetal malformations. At least one CTG was performed in each of the following intervals: 24-26 weeks+6 days, 27-29 weeks+6 days, 30-32 weeks+6 days, 33-35 weeks+6 days, 36-38 weeks+6 days and ≥39 weeks. Tracings were analyzed using the Omniview-SisPorto® 3.6 system. Cases with a normal pregnancy outcome, including a birthweight ≥10th percentile for gestational age, were compared with two groups of SGA fetuses: with birthweight <10th percentile (SGA<p10) and <3rd percentile (SGA<p3; a subgroup of the latter). Generalized linear mixed-effects models were used for analysis.

RESULTS: A total of 176 fetuses (31 SGA) and 1256 tracings (207 from SGA fetuses) were evaluated. All CTG parameters changed significantly throughout pregnancy in the three groups, with a decreasing baseline and probability of decelerations, and an increasing average long-term variability (LTV), average short-term variability (STV) and accelerations. Baseline showed a more pronounced decrease (steeper slope) in SGA fetuses, being higher in these cases at earlier gestational ages and lower later in pregnancy. Average LTV was significantly lower in SGA<p3 fetuses, but a parallel increase occurred in all groups. There was a considerable inter-fetal variability within each group.

CONCLUSION: A unique characterization of CTG trends throughout gestation in SGA fetuses was provided. A steeper descent of the baseline was reported for the first time. The findings raise the possibility of clinical application of computerized CTG analysis in screening and management of fetal growth restriction.