The article by Vintzileos and Smulian highlights the importance of longitudinal assessment of fetal heart rate (FHR) patterns. This is quite unlikely to be the key eluding us for 60 years because, to be fair, most front-line clinicians do inherently consider FHR changes over time during labor in a practical way rather than just cross-sectionally. Nevertheless, the judgment about any intervention remains complex.

The studies on longitudinal FHR changes would be very desirable but may be problematic. With no need for prospective study/control groups, a robust retrospective study design would suffice. Hence, such studies could (should) be done on already available clinical material/data. However, could the study methodology (eg, the definition of normal versus abnormal longitudinal patterns) be so imprecise and subjective as to render the results inconclusive? Many studies with less complex methodology involving cross-sectional cardiotocography (CTG) interpretation have been inconclusive.

The article acknowledges the major drawback of the American 3-tier system that category III is too late to intervene. Second, the distinction between absent and reduced FHR variability (<5 beats per minute) is often difficult and clinically unimportant. Hence, a 3-tier system (similar to the United Kingdom), which classifies persistent reduced variability or pathological decelerations into the pathological/III category seems more useful clinically. The British system also classifies a combination of multiple milder FHR abnormalities into the pathological category. However, it needs to be supplemented by a further confirmatory test like fetal stimulation test or fetal scalp blood sampling because of the low positive predictive value of the pathological category of CTG.

Postdeceleration overshoots (apart from being extremely rare) seem unimportant because two recent well-designed large clinical studies confirmed complete lack of correlation with fetal acidemia. Only 1 out of 5331 nonacidemic fetuses and none out of 57 acidemic fetuses had “overshoots”. Moreover, the theoretical basis for these “overshoots” arises from animal experiments where umbilical cord was occluded for 2 minutes every 4 minutes – not relevant to human labor except in worst cases of cord prolapse. Benign FHR decelerations during the expulsive second stage are common; hence, progression from category I to II based on those should not warrant operative intervention. The overriding emphasis on the loss of FHR variability (considering about 90% of babies born with pH <7.10 have normal FHR variability ) may reflect shortcomings with meaningful interpretation of FHR decelerations, which are center stage in CTG interpretation.

The British 3-tier system functioned well when the subcategorization of FHR decelerations was based primarily on time relationship to contractions as by Hon. Should early decelerations be defined as gradual despite the fact that head compression (and other nonhypoxic reflex mechanisms) actually causes rapid decelerations? Should all rapid decelerations be defined as variable despite the fact that the decelerations in confirmed cord compression (predominant chemoreceptor mechanism) have descent time often much more than 30 seconds with nadir much later than peak of contractions? Could these be some of the most substantial framing and confirmation fallacies in modern medicine?

The categorization of FHR decelerations is a theoretical/conceptual framework. If it contradicts careful observations and critical analysis, then it would be incompatible with the scientific method/approach and best be corrected for any system of CTG interpretation to be meaningful.