Identification of Clusters of Prenatally Detected Fetal Defects in the San Joaquin Valley of California

Abstract

Objective:

This retrospective study using a causal-comparative design addressed the question: Can clusters of prenatally detected defects be identified, based on a sample of fetal sonographic reports, for maternal patients that reside in rural and urban regions across five counties in the San Joaquin Valley of California?

Materials and Methods:

The fetal defects were identified by advanced perinatology sonography students and graduates who retrospectively reviewed a purposeful sample of 8667 obstetrical sonographic or fetal echocardiographic reports between October 30, 2024, and April 30, 2025. The reports were based on those maternal patients who were examined and resided in the counties of Fresno, Kings, Madera, Merced, and Tulare, California.

Results:

A total of 414 structural fetal defects (e.g., cardiac, ventral, cerebral/central nervous system (CNS), skeletal, renal, growth restriction, masses/tumors) were reported. Based on the record review, fetal cardiac abnormalities were the most frequently identified (229/414, 55.3%). Chromosomal (57/327, 17.4%) and multiple fetal abnormalities (89/395, 22.5%) were also commonly reported. The standardized incidence ratio of fetal defects in the sampled region of the San Joaquin Valley (414/8667, 4.8%) was greater than the national average incidence rate of birth defects (3.0%). The approximate prevalence rates of fetal defects in the populations of the San Joaquin Valley (2.0% in urban regions and 6.3% in rural regions) were greater than the global prevalence rate of congenital birth defects (1.57%).

Conclusion:

Clusters of fetal defects were identified, specifically in the urban regions of Fresno and Tulare counties. Further research is recommended to evaluate the effects of multiple potential factors (e.g., maternal age, race/ethnicity, socioeconomic status, delays in detection, environmental exposure to agricultural/industrial chemicals, contaminated water or air, and drug abuse) to explain this cohort of fetal defects that developed in the San Joaquin Valley.