Evidence of lower oxygen reserves during labour in the growth restricted human foetus: a retrospective study

The aim of the present study is to test the hypothesis that Growth Restricted foetuses (FGR) have the tendency to develop more pathological cardiotocograpic tracings during labour than do appropriate for gestational age foetuses and that there is a shorter time lapse from the beginning of labour and the advent of a pathological cardiotocograpic tracing.

The study was carried out at the Maternal-Foetal Medicine Unit of the Sant'Anna University Hospital, Turin, Italy. A total of 930 foetuses born at term between January and December 2012 were analysed: 355 small for gestational age (SGA) comprising both constitutional small for gestational age and growth restricted foetuses (cases group) and 575 Appropriate for Gestational Age (AGA) foetuses (control group). Tracings were evaluated independently by two obstetric consultants, according to the International Federation of Gynaecology and Obstetrics (FIGO) classification. The main outcomes considered were the incidence of pathological cardiotocograpic tracings and the time interval between the beginning of labour and the advent of pathological cardiotocograpic tracing. The Student's t-test, chi-square test and ANOVA were used for comparisons between cases and controls and amongst groups. Significance was set at <0.05. Univariate and multivariate odds-ratios were calculated.

Foetuses with birthweight <3rd centile (growth restricted foetuses) more frequently presented pathological cardiotocograpic tracings in labour than did controls (43.8% vs. 21.6%; p < 0.001). Pathological cardiotocograpic tracing developed faster in the foetuses with birthweight <3rd centile group (53', 0'-277') than it did in the control group (170.5', 0'-550'; p < 0.05). A higher induction rate was observed in the cases (29.6%) than in the control group (17%), with statistical significance p < 0.001. To correct for this possible confounding factor a multivariate logistic regression analysis was performed. It confirmed a statistically significant increased risk of pathological cardiotocographic tracings in the FGR group (OR 1.63; CI 1.30-2.05).

The results confirm the hypothesis that Growth Restricted foetuses (FGR) have fewer oxygen reserves to deal with labour. Our results underscore the importance of the prenatal detection of these foetuses and of their continuous cardiotocographic monitoring during labour.