The National Zoo’s 17-year-old giant panda Mei Xiang had an ultrasound this morning and Zoo veterinarians are excited, suggesting that she really just might possibly be pregnant.
The four centimeter fetus could potentially be reabsorbed or worse, the panda could possibly miscarry. And earlier this week, the research vet on the case Pierre Comizzoli cautioned that the ultrasound could even be picking up bamboo fiber.
If you haven’t been following the #pandastory, which detailed the artificial insemination of the mother panda in May, you probably don’t understand why this news of the ultrasound is such a big deal. Let’s bring you up to speed.
For starters, Mei Xiang had been refusing to even allow keepers to conduct ultrasound examinations. But this morning, the Zoo reports, she responded to the familiar calls of her keepers and allowed them to conduct the procedure.
Of course the birth of any panda is significant because there are fewer than 2,000 total pandas— captive and wild— left in the world. But breeding pandas is complicated and frustrating. Mei Xiang has only given birth just four times in the past ten years. (One cub succumbed to a lung and liver failure in 2012 and another was stillborn in 2013.)
Comizzoli says that a female giant panda bear only experiences one ovarian cycle per year. During that time, which is usually between March and May, there is a window of about 36 hours when she can become pregnant. If she does become pregnant, the embryo will develop through a process called embryonic dispausal or delayed implantation. This means that the embryo will pause development for the following three to five months to allow the mother to give birth at the optimal time says Comizzoli. After those few months, the embryo resumes development for around 45 to 50 days before birth.
Over the past few weeks, veterinarians have followed the progress of the giant panda’s pregnancy by measuring the levels of the hormone progesterone in her system. Those levels rise significantly in the second phase of embryonic development alerting the mother that she should prepare to give birth. That’s why the Smithsonian Conservation Biology Institute’s early August confirmation of Mei Xiang’s increasing progesterone levels sparked an international frenzy about a potential new cub.
Unfortunately for everyone following the #pandastory, and perhaps most unfortunate for Mei, those rising progesterone levels could have indicated, however, that she is not pregnant.
Experts call this phenomenon a pseudopregnancy, of which Mei has had six. During the pseudopregnancy, “the exposure to high progesterone induces specific behaviors in the mother and she’s going to behave like she was really expecting a baby,” says Comizzoli. “So she’s going to start to build a nest and she’s going to start to stay in her den for longer periods of time.” If no cub is born within the hours or days after those progesterone levels decrease, then the mother was never pregnant.
Other than mistaking bamboo fiber for a fetus, ultrasounds can be unreliable, Comizzoli says, because panda cubs are so tiny—weighing less than a pound at birth.
The veterinarians rarely anesthetize Mei Xiang to perform an ultrasound. Rather she has to be a willing participant. So it was not an unusual behavior in early-August for her to start to refuse the tests, “that’s just her character,” according to Comizzoli who has worked with her since 2004.