We are so pleased to learn of the birth of Zoo Atlanta’s newest panda cub. The 3-D pictures of Lun Lun’s cub in utero certainly were amazing. This advanced imaging is normally used in humans to detect skeletal and cardiovascular defects, but has become popular among human parents-to-be for getting a “sneak peek” at what their baby may look like at birth. Should our own Bai Yun become pregnant again, it is possible that we will also invite a local expert to help us obtain 3-D images of a cub (or cubs), as we do not currently own equipment that allows us to capture these images. In our case, 3-D imaging would not replace our routine 2-D ultrasound scanning to monitor the growth of Bai Yun’s fetus(es).
In addition to the standard tests our veterinarians and researchers would run to monitor Bai Yun’s health and pregnancy status after breeding, we will certainly measure her ceruloplasmin levels. This protein may give us information about the presence of a fetus before our standard tests are able to detect a pregnancy.
We have seen with thermal imaging and ultrasound that many giant panda pregnancies are lost during gestation. There are a few reasons that a fetus might be reabsorbed. Fetal defect or death, uterine disease, maternal disease, or hormonal disruption of a pregnancy could all cause a fetus to be reabsorbed. This phenomenon is widely reported in mammals, including humans. During the process of reabsorption, the fetus breaks down in the uterus and through natural processes is eliminated. In Bai Yun’s pregnancies, when a twin died our veterinarians did a follow-up ultrasound to verify that no fetal tissues remained in the uterus.
Our vets and animal care staff continually monitor Bai Yun’s health, so we can rule out maternal or uterine disease as a factor in fetal resorption. In our endocrine lab we monitor Bai Yun’s hormone levels and know that there were no deviations from the normal pregnancy profile. With ultrasound we have been able to see fetuses begin to break down and sometimes disappear completely. But the exact cause of fetal death in giant pandas is still a mystery. Through our work with ultrasound and thermal imaging, we suspect that Bai Yun routinely conceives multiple fetuses, then reduces that number to one through a process called “prenatal litter pruning.” Because it is very rare that a giant panda mother raises more than one cub, there may be a mechanism within the uterus that reduces a multiple pregnancy to a singleton before birth about 50 percent of the time.
There is no evidence that twinning is more common following artificial insemination (AI). With our own Bai Yun, we know she was pregnant with twins (or even triplets in one case) following natural breeding. The fact that she gave birth to a single offspring was not related to the method of insemination (artificial or natural). Some giant panda researcher believe that artificial insemination following natural breeding will increase the incidence of twins, but there are no data to support this belief. Regardless of our ever-improving AI techniques and timing, it is not a substitute for natural breeding! The male giant panda always knows the right time for insemination, and fresh, unprocessed sperm is always the most fertile.