To save babies from suffocation, scientists study sheep births
In human babies, a lack of oxygen during birth can have tragic consequences. This suffocation, called fetal asphyxia, can cause severe brain damage and stillbirth. To better understand the causes of fetal asphyxia, a team of Uruguayan scientists recently conducted a study of sheep, an animal that closely resembles humans during birth.
Like in humans, the availability of oxygen to lambs depends on oxygen transfer from the mother’s blood supply through the placenta and umbilical cord. Sheep are often studied as models for human pregnancies because their placentas are similar. Drs. Fernando Dutra and Georgett Banchero studied whether factors like duration of birth, fetal body weight and birth order affected rates of fetal asphyxia in sheep. In a study published in the October issue of the Journal of Animal Science, Dutra and Banchero reported that a prolonged duration of birth is closely tied to a lack of oxygen for the newborn.
Prolonged birthing time harmed the lambs in several ways. The longer birth took, the greater the risk of damage to the placenta, umbilical cord compression and decreased maternal oxygen. These factors led to asphyxia in the lambs.
To test oxygen conentration, the researchers analyzed blood samples from the newborn lambs. They also performed Apgar tests, tests of reflexes and appearance originally designed to evaluate the health of human infants.
“Approximately 30% of the newborn lambs evaluated with the modified Apgar tests in this experiment had a low or medium viability score at birth,” wrote the researchers. “These data coincide with the number of lambs that were born asphyxiated.”
Another major risk-factor for asphyxia was the birth of twins. According to the study data, twin-born lambs had a “16-fold greater risk of asphyxia.”
These data from sheep are similar to the risks for human twins. According the Dr. Michael Ross, a professor of obstetrics, gynecology and public health at UCLA, the risk of fetal distress for human twins leads many doctors to reduce birthing duration through Cesarean sections.
“The more we get into multiple births, the more we get into C-Sections,” Ross said in an interview.
Ross said that in cases of twins, one baby might be smaller than the other, and this smaller baby may be more susceptible to asphyxiation. He said fetal asphyxia is a risk with any pregnancy.
“It’s the main reason we monitor the heart rate during birth,” said Ross.
In humans, Ross explained, duration of birth is not actually a risk for the baby. A prolonged birth just means there is more time for things to go wrong. Ross has also performed studies of sheep in labor. He says sheep are helpful models for human births because their fetal physiology is similar.
“Sheep are an excellent model,” he said. “Even how labor begins is studied in sheep.”
Now that Dutra and Banchero have linked birth duration and multiple births to risk for asphyxia, they hope to study other factors in ewes and lambs that could cause suffocation. Their work could help sheep producers, and perhaps doctors like Ross, deliver healthy infants.
This study is titled “Polwarth and Texel ewe parturition duration and its association with lamb birth asphyxia.” It can be read in full at http://journalofanimalscience.org/
ASAS Scientific Communications Associate
MadelineMS@asas.org / 217-689-2435