Home pregnancy tests have made it easy to find out when a woman is expecting.

But as this ScienCentral News video reports, things are a lot more complicated if you’re a giant panda.

So unlike humans

The fact that giant pandas can only become pregnant once a year in a two- or three-day window isn’t the only thing hindering the breeding process, says Nancy Czekala of the San Diego Zoo. There are other complications of impregnating pandas in captivity: They live mostly solitary lives, only come together to mate, and have to be mutually interested if they are to mate without artificial insemination (San Diego’s male, Shi Shi, does not like the female, Bai Yun).

Also, information about the timing of a panda’s pregnancy and delivery is crucial to breeders in order to have proper support on hand. Giant Panda mothers typically will raise only one of the babies if they have twins, which happens in at least 40 percent of captive births.

Unfortunately, panda pregnancies are extremely difficult to detect. Human pregnancies can be foretold by several means: ultrasound, the telltale expanded belly, and hormones collected from urine in a typical home-pregnancy test. None of these work for pandas—they generally won’t sit still for ultrasounds, their babies are born too small (the size of a stick of butter) to create any noticeable belly under the panda’s fur, and their pregnancy hormones remain mysterious.

Researchers trying to discover a pattern to the hormones typical to a panda’s pregnancy have few examples to draw from; only about 150 pandas live in zoos around the world, and few were born in captivity. The scant patterns that have been found indicate that a pregnant panda’s urine hormones track exactly to a non-pregnant panda’s, except for a four- or five-day period about 30 days before delivery.

The change in hormones is thought to correspond to the implantation of the panda fetus, another mysterious event. Called variable delayed implantation, this phenomenon of pandas means that the embryo floats freely in the uterus until, researchers think, conditions for a successful birth are deemed to be favorable and the fetus implants in the wall of the uterus late in the three-to five-month pregnancy. A human embryo implants within days of fertilization.

Czekala’s colleague, Lee Hagey, has developed a new way to use an old machine to monitor levels of chemicals in a panda’s urine. The machine separates chemicals in the urine out according to weight and gives a computerized profile of the amounts of each chemical in the sample. In addition, researchers are focusing on a new set of steroid hormones as possible markers of pregnancy. Hagey and Czekala are hopeful that together, these will prove to be a more reliable technique than prior methods.

Good news abroad

Twins pandas were born on August 20 at the Giant Panda Breeding Research Center, located in the southwestern Sichuan Province of China. The center also reports that nine other pandas are expected to give birth within the next month. Nearby Wolong Nature Reserve says four of their pandas are expecting this year as well. However, as their detection methods could prove as unreliable as the San Diego Zoo’s, only the appearance of pink panda cubs will provide proof of panda pregnancy.