Monitoring Fetal Growth via Ultrasonography

Ultrasonography is a valuable tool for detecting pregnancy and establishing pregnancy loss, but it can also be used to evaluate equine fetal growth, said W.K. (Karin) Hendriks, DVM, Dipl. ECAR. Veterinarians could use a combination of transrectal and transabdominal ultrasounds to provide good information about fetal development.

Because it is difficult to define normal development for gestational age in a fetus, Hendriks and her colleagues in the Department of Equine Sciences at Utrecht University in The Netherlands evaluated 32 Dutch Warmblood mares from 100 days of gestation until parturition to see which maternal factors influence fetal development and to find parameters other than fetal aorta diameter to predict gestation length.

"Maternal age and parity both affect fetal development," said Hendriks. "For example an older mare (greater than 15 years of age) will bring a smaller foal to term than a young (around 5 years of age) mare."

The researchers found that the ventral uterine wall and placenta (CTUPv) close to the cervix was thicker in mares carrying their first foal (primiparous) than in multiparous mares between 100 and 250 days of gestation. After day 220 the cross-sectional area of the eye orbit and cranium was greater in primiparous than in multiparous mares.

The fetal aorta diameter was smaller in older mares than in younger mares. The cross-sectional surface area of the cranium and the aorta diameter increased linearly throughout late gestation and could be used to predict gestation length.

"The parameters CTUPv, eye orbit diameter, eye orbit cross-sectional surface area, biparietal diameter, biparietal cross-sectional surface area, aorta diameter, and fetal heart rate are relatively easy to evaluate with simple, portable ultrasound machine of a type affordable for most practices," she said.

The aorta diameter, biparietal cross-sectional surface area, and CTUPv increase linearly during late gestation. While these parameters could be useful for monitoring fetal growth and development, they are influenced by maternal age or parity, and varied considerably among horses in the study. Taking measurements through gestation might more accurately predict gestation length or better identify abnormal fetal development.

The study, "Maternal age and parity influence ultrasonographic measurements of fetal growth in Dutch Warmblood mares," was published in the October issue of Animal Reproduction Science. The abstract is available on PubMed.  

About the Author

Marie Rosenthal, MS

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