Analysis of Risk Factors Influencing Imminent Distress in Growth-Retarded Fetuses Undergoing Oxygen Test

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Abstract
We previously demonstrated a prognostic significance of maternal oxygen test in predicting imminent fetal distress. The purpose of this study was to investigate eventual other factors related to the length of the time interval elapsing between the Doppler diagnosis of brain sparing effect and abnormal fetal heart rate patterns. To this end we considered 101 growth-retarded fetuses free of structural and chromosomal abnormalities with a ratio between the pulsatility indices of umbilical and middle cerebral artery above the 95th centile in presence of a normal fetal heart rate pattern. The factors, other than the oxygen test, analyzed for a potential influence on this time interval were gestational age, presence of hypertension or preeclampsia, amniotic fluid index, severity of growth retardation (centile of the ultrasonographic estimated fetal weight) and 9 different Doppler indices calculated from extra- and intracardiac districts. Statistical actuarial methods were used to determine the effect of these prognostic factors on the duration of this time interval. The occurrence of abnormal fetal heart rate patterns (antepartum late heart rate decelerations) was used as censoring variable. The time interval between the entry in the study and delivery ranged from 1 to 39 days. Indications for delivery were fetal distress in 53 fetuses (52.4%) and different maternal or fetal complications in the remaining 48 fetuses. Multivariate analysis showed that the factors that independently affect the time interval between Doppler abnormalities and development of abnormal fetal heart rate patterns are the oxygen test (p ≤ 0.001), the percentage of reverse flow in inferior vena cava (p ≤ 0.001), gestational age (p ≤ 0.01) and the presence of hypertension (p ≤ 0.05). The knowledge of these prognostic factors may be useful in the clinical management of growth-retarded fetuses.

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