Ten FETO patients and 22 control patients met inclusion criteria. Demographic and clinical characteristics are described in Table 1. Fetal observed/expected lung-to-head ratio was lower in FETO patients compared to controls [median (25%, 75%): 21.7 (21.4, 25.6) vs. 24.9 (23.5, 27.7), p = 0.06] as was gestational age at delivery [35.1 (34.5, 36.2) vs. 39.2 (38.8, 39.6), p < 0.001]. Extracorporeal membrane oxygenation (ECMO) utilization and pulmonary hypertension medications at discharge were lower in the FETO group compared to control patients (ECMO: 30% vs. 64%; medications: 0% vs. 27%), although these findings did not reach statistical significance. Overall survival was 90% in the FETO group and 82% in the control group.

At first echocardiogram, both groups demonstrated RV systolic dysfunction measured by low TAPSEZ, RVFAC, and RV strain (Table 2). RV/LV ratio and LVEI were lower in FETO patients compared to control patients [RV/LV: 1.10 (1.03, 1.24) vs. 1.57 (1.26, 1.76), p = 0.01 and LVEI 1.50 (1.38, 1.57) vs 1.94 (1.56, 2.31), p = 0.01], reflecting less RV dilation and less ventricular septal displacement, respectively. LV hypoplasia measured by 2-dimensional M-mode Z-scores was less severe in FETO patients compared to control patients [LVIDDZ − 2.12 (− 3.07, − 1.41) vs. − 3.50 (− 4.48, − 2.72), p = 0.01 and LVIDSZ − 1.55 (− 2.56, 0.80) vs. − 3.93 (− 4.69, − 2.67), p = 0.01]. While LV shortening fraction was lower in FETO patients [31.0 (25.0, 36.0) vs. 44.5 (36.0, 48.7), p = 0.02], LV function measured by GLS was similar.

The directionality of the effects noted at baseline were similar in the immediate pre-operative period, but there were no statistically significant differences in RV size or ventricular function between the two groups.

In the post-operative period, FETO patients demonstrated better RV function compared to control patients as measured by RVFAC [44.8 (42.8, 49.4) vs. 36.8 (29.4, 39.9), p < 0.01], RVGLS [24.8 (19.9, 26.6) vs. 19.5 (17.3, 21.2), p = 0.02], and RVFWS [28.5 (22.5, 31.5) vs. 23.3 (18.7, 26.3), p = 0.05] (Table 3). However, at last available echocardiogram there were no longer any differences in RV size or ventricular function between the two groups.

Changes in ventricular size and function from first to last echocardiogram differed between the groups. FETO patients demonstrated smaller increases in LV size measured by LVIDDZ and LVIDSZ compared to control patients (Table 4, Fig. 2). At last available echocardiogram, the increases in LVIDDZ and LVIDSZ from baseline were on average 2.22 and 2.75 units smaller, respectively, in the FETO patients than the control patients. RV/LV ratio and LVEI (adjusted for LV size) improved over time in both groups, but the improvements were greater in the FETO group on average (Table 4, Fig. 3). Improvements in RV function by TAPSEZ, RVFAC, RVFWS, and RVGLS were similar between the groups.

Changes in LV Z-scores for FETO and control patients. At last available echocardiogram, the increases in LVIDDZ and LVIDSZ were on average 2.22 and 2.75 units smaller, respectively, in the FETO patients than the control patients

Changes in RV/LV ratio and LVEI for FETO and control patients. RV/LV ratio and LVEI decreased over time from first to last echocardiogram, and the decrease was greater in the FETO group on average