To evaluate the interobserver variability of lung to head ratio (LHR) during pregnancy in fetuses with left congenital diaphragmatic hernia (CDH), at different levels of LHR. LHR was taken in 29 fetuses with isolated CDH without prenatal intervention with a mean of gestional age (28.7 w), by two independent observers. Reproducibility was evaluated by the interclass correlation coefficient (interCC) and limits of agreement. Reproducibility was assessed in three groups: group A, LHR: < 1.0, group B, LHR: 1.0–1.4 and group C, LHR: > 1.4. Overall, there was a good inter-observer agreement, with an interCC of 0.89 p < 0.0001, 95%CI: 0.77–0.94 and limits of agreement of—0.38, 0.51. The limits of agreement decreased with LHR values (group A, − 0.29, − 0.25, group B, − 0.38, 0.51, group C − 0.51, 0.66). Interobserver agreement for LHR is globally high, showing narrow limits of agreement at the most clinically relevant interval of LHR < 1.0.