Sources of heterogeneity when studying the cardiovascular effects of fetal growth restriction: an overview of the issues.

Intrauterine growth restriction (IUGR) has been repeatedly identified as a risk factor for cardiovascular disease (CVD). A possible explanation for this association is the effect of IUGR on cardiovascular structure and function. However, the specific changes observed are not consistent among studies. In this paper, we analyze several sources of heterogeneity within and between studies related to exposure, outcome and co-variables. A broad IUGR definition might include different phenotypes, expressing heterogeneity as an outcome. Outcome heterogeneity may also be the result of the postnatal effect modification that can be explored within studies. In order to do so, it is important to move beyond mean differences between groups, for example using unsupervised, stratified or interaction analysis. Different definitions of IUGR and the inclusion of different postnatal variables as confounders are potential sources of heterogeneity between studies. Researchers should be aware that postnatal variables may play different roles throughout a person's life and are not limited to behave as confounders. Therefore, their inclusion in the statistical model needs to be carefully considered. We discuss when sources of heterogeneity need to be controlled, and when they need to be identified and shown as a result.

Characterizing cardiac dysfunction in fetuses with left congenital diaphragmatic hernia.

OBJECTIVE: To evaluate cardiac function by conventional echocardiography and tissue Doppler imaging in fetuses with left congenital diaphragmatic hernia (CDH). METHODS: Conventional echocardiography (myocardial performance index, ventricular filling velocities, and E/A ratios) and tissue Doppler imaging (annular myocardial peak velocities, E/E' and E'/A' ratios) in mitral, septal, and tricuspid annulus were evaluated in a cohort of 31 left-sided CDH fetuses and compared with 75 controls matched for gestational age 2:1. RESULTS: In comparison to controls, CDH fetuses had prolonged isovolumetric time periods (isovolumetric contraction time 35 ms vs 28 ms, P < .001), with higher myocardial performance index (0.49 vs 0.42, P < .001) and tricuspid E/A ratios (0.77 vs 0.72, P = .033). Longitudinal function assessed by tissue Doppler showed signs of impaired relaxation (mitral lateral A' 8.0 vs 10.1 cm/s, P < .001 and an increased mitral lateral E'/A' ratio 0.93 vs 0.78, P < .001) in the CDH fetuses as compared with controls, with preserved systolic function. CONCLUSION: Left CDH fetuses show echocardiographic signs of diastolic dysfunction, probably secondary to fetal heart compression, maintaining a preserved systolic function.

Risk of perinatal death in early-onset intrauterine growth restriction according to gestational age and cardiovascular Doppler indices: a multicenter study.

OBJECTIVE: To assess the value of gestational age and cardiovascular Doppler indices in predicting perinatal mortality in a multicenter cohort of early-onset intrauterine growth-restricted (IUGR) fetuses. METHODS: A multicenter prospective cohort study including 157 early-onset (<34 weeks) IUGR cases with abnormal umbilical artery (UA) Doppler was conducted. Cardiovascular assessment included the ductus venosus (DV), the aortic isthmus flow index (IFI), and the myocardial performance index (MPI). Isolated and combined values to predict the risk of perinatal death were evaluated by logistic regression and by decision tree analysis, where the gestational age at delivery, UA, and middle cerebral artery (MCA) were also included as covariates. RESULTS: Perinatal mortality was 17% (27/157). All parameters were significantly associated with perinatal death, with individual odds ratios (OR) of 25.2 for gestational age below 28 weeks, 12.1 for absent/reversed DV atrial flow, 5.3 for MCA pulsatility index <5th centile, 4.6 for UA absent/reversed diastolic end-flow, 1.8 for IFI <5th centile, and 1.6 for MPI >95th centile. Decision tree analysis identified gestational age at birth as the best predictor of death (<26 weeks, 93% mortality; 26-28 weeks, 29% mortality, and >28 weeks, 3% mortality). Between 26 and 28 weeks, DV atrial flow allowed further stratification between high (60%) and low risk (18%) of mortality. CONCLUSIONS: Gestational age largely determines the risk of perinatal mortality in early-onset IUGR before 26 weeks and later than 28 weeks of gestation. The DV may improve clinical management by stratifying the probability of death between 26 and 28 weeks of gestation.

Cerebral venous blood flow in growth restricted fetuses with an abnormal blood flow in the umbilical artery before 32 weeks of gestation.

OBJECTIVE: To evaluate the brain venous circulation in fetuses with severe intrauterine growth restriction (IUGR) before 32 weeks of gestation. STUDY DESIGN: Fifty fetuses with severe IUGR diagnosed between 27 and 32 weeks of gestation and 50 appropriate-for-gestational age (AGA) fetuses matched by gestational age were evaluated. IUGR fetuses were classified according to their hemodynamic deterioration pattern in relation to the Doppler examination of the umbilical artery (UA), middle cerebral artery (MCA) and ductus venosus (DV). The fetal venous brain blood flow was evaluated in the vein of Galen (VG), superior sagittal (SS), straight and transverse venous sinuses. RESULTS: Only the transverse sinus (TS) showed a significant reduction in the pulsatility index (PI) values in IUGR fetuses. All other veins showed similar PI values between IUGR and AGA fetuses. All cerebral veins of IUGR fetuses showed significantly increased maximum and mean velocities. All these findings did not change in relation to the hemodynamic IUGR deterioration. In nearly all normal and all IUGR fetuses, a pulsatile blood flow pattern was observed in the straight and transverse sinuses, whereas an increased pulsatile pattern in the VG and in the SS was noted in IUGR fetuses. CONCLUSION: Brain venous blood flow in IUGR fetuses shows an increment in the maximum and mean velocities of all veins and a reduction in the PI in the transverse sinus.