Sure, the cherry blossoms are D.C.’s most famous sign of spring. But locals finely tuned in to the reproductive cycle of the National Zoo’s most famous residents know another certain mark of the season: discussion of urinary hormone analysis and panda artificial insemination.

After indication that the zoo’s female giant panda, 20-year-old Mei Xiang, was experiencing an increase in estrogen levels and engaging in “breeding behavior,” scientists took advantage of a very small fertility window to artificially inseminate her with long-time partner Tian Tian’s semen.

Though previous reports showed Tian Tian was taking strides to be present and helpful to his furry companion, the two have always had a rocky breeding relationship. “Mei Xiang made it clear she wasn’t interested in spending time with Tian Tian until yesterday. We usually listen to her and give her what she needs in that moment. Over the many breeding seasons we’ve learned that the two aren’t compatible mates,” said National Zoo spokesperson Devin Murphy. But they’ve successfully used artificial insemination in the past.  

Mei Xiang is nearing the end of her reproductive years, and veterinarians have been hoping to see another cub before the loan agreement between the National Zoo and the China Wildlife Conservation Association ends in 2020. But they won’t know if the artificial insemination took for another three to six months.

Scientists will begin giving Mei Xiang ultrasounds this summer to try to determine if the pregnancy is real. But it’s often nearly impossible to confirm because of the nature in which pandas carry their babies, showing signs of pregnancy without being pregnant—called pseudopregnancy. Giant pandas are also very small at birth, weighing about three to five ounces.

Mei Xiang last gave birth in 2015, to Bei Bei. Since then, she’s had two pseudo-pregnancies.

A potential cub would make the couple’s fourth child together. Mei Xiang’s other children, Bao Bao and Tai Shan, are both in China as part of the loan agreement, which returns cubs at the age of 4. Bei Bei is expected to join his siblings sometime within the next year as he approaches his fourth birthday in August.