New fetal heart valve growth charts unveiled for mid-pregnancy ultrasound scans

Researchers have built gestational age-specific reference ranges and Z-score equations for the diameters of the fetal aortic and pulmonary valve annuli between 18 + 0 and 24 + 6 weeks of gestation, using data from a routine second-trimester screening population. The work, published as an open access study in Archives of Gynecology and Obstetrics, also examined the ratio between the two valve diameters as a marker of proportionate semilunar valve growth during standard anomaly scanning.

This design choice matters for measurement consistency: valve annuli are small structures, typically a few millimeters across at this stage of pregnancy, and variation between operators can rival the biological differences the measurements are meant to detect.

The resulting equations were AV = 2.9273 + 0.0342 × (GA − 150), with an R² of 0.370, and PV = 3.6650 + 0.0420 × (GA − 150), with an R² of 0.395. In practical terms, each additional day of gestation was associated with an average increase of about 0.034 mm in the aortic valve annulus and about 0.042 mm in the pulmonary valve annulus, with the pulmonary valve running larger than the aortic valve throughout the window. The moderate R² values indicate that gestational age explains roughly a third to two-fifths of the variation in these diameters, leaving substantial individual variability that reference ranges are designed to accommodate.

This approach tests whether the equations generalize to fetuses that played no role in building them, rather than simply describing the same data they were derived from.

The validation results were close to statistical ideals. In held-out data, the pooled mean Z-score was +0.023 (standard deviation 1.048) for the aortic valve and +0.016 (standard deviation 1.046) for the pulmonary valve, against nominal values of 0 for the mean and 1 for the standard deviation. Some 93.86 percent of aortic valve observations and 93.49 percent of pulmonary valve observations fell within ± 1.96 Z-score units, compared with the nominal 95 percent. Z-scores express how far a given measurement sits from the gestational age-specific expected value, in units of standard deviations, which allows clinicians to interpret a raw millimeter reading against the distribution expected for that exact day of pregnancy.

The mean ratio was 1.262 (standard deviation 0.146) and remained stable across gestation, with an R² below 0.001. In other words, the pulmonary valve annulus was on average about a quarter larger than the aortic valve annulus, and this proportional relationship did not meaningfully change between 18 and 24 weeks. The authors suggest this stability may make the ratio an additional parameter for assessing proportionate semilunar valve growth during routine anomaly scanning.

Why does this matter? Fetal cardiac anomalies can involve semilunar valves that are too small, too large, or disproportionate to one another, and interpreting any single measurement requires knowing what is normal for the gestational age in question. Reference ranges and Z-score equations of this kind provide the statistical backbone for such judgments in the second trimester, when detailed anomaly scans are typically performed. Because the equations were derived from a routine screening population rather than a selected high-risk cohort, they are intended to reflect the fetuses most commonly encountered in everyday practice.

The authors conclude that these internally validated reference ranges and Z-score equations may support standardized second-trimester assessment of fetal semilunar valve dimensions. As with any single-center retrospective study, the findings describe one population and one measurement protocol, and the reported equations are presented as tools to support, not replace, clinical assessment during routine mid-pregnancy ultrasound examination.

Subject of Research: Gestational age-specific reference ranges and Z-score equations for fetal aortic and pulmonary valve annulus diameters in the second trimester

Article Title: Gestational age-specific reference ranges and Z-score equations for fetal aortic and pulmonary valve annulus diameters at 18–24 weeks of gestation

Article References: Beyhekim, F., Beyhekim, H., Soykan Sert, Z., Örgül, G., Taşpınar, M. N., & Tazegül Pekin, A. (2026). Gestational age-specific reference ranges and Z-score equations for fetal aortic and pulmonary valve annulus diameters at 18–24 weeks of gestation. Archives of Gynecology and Obstetrics. https://doi.org/10.1007/s00404-026-08596-9

Image Credits: AI Generated

DOI: 10.1007/s00404-026-08596-9

Keywords: fetal echocardiography, aortic valve annulus, pulmonary valve annulus, Z-score equations, reference ranges, second trimester, anomaly scan, PV/AV ratio, gestational age, cross-validation, fetal heart, prenatal screening