BOSTON (CBS) – An ultrasound on a gorilla at Franklin Park Zoo confirmed that the primate is expecting her fourth baby this spring.

Workers used an over-the-counter home pregnancy test to confirm that Kiki, one of the zoo’s seven western lowland gorillas, was indeed expecting. Her due date is sometime in May.

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Zoo staff has also been able to perform ultrasounds on the gorilla. According the zoo officials, Kiki held her belly up to the mesh while zookeepers and veterinarians performed the test.

“We’re thrilled to share this wonderful news with everyone. Kiki is a very experienced mother, and our visitors will have the unique opportunity to watch this baby grow up and observe the family dynamics,” said Zoo New England President and CEO John Linehan.

According to Franklin Park Zoo, western lowland gorillas are considered “critically endangered” in the wild.

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The species is found in Nigeria, Cameroon, Gabon, Equatorial Guinea, Republic of Congo, Angola, and Central African Republic.

Kiki’s daughters Kimani and Kambiri reside in the Tropical Forest Pavalion while her oldest child, Kira, was moved two years ago into the Philadelphia Zoo.

“Kiki, who last gave birth in 2010, is doing great so far but, as with any pregnancy, we are carefully monitoring her health as her pregnancy progresses. Through the ultrasounds we have been able to see that the baby is active with a steady heartbeat, which are both very good signs,” said Zoo New England Associate Veterinarian Dr. Susie Bartlett. “The staff has done an incredible job with the training programs, which play an instrumental role in assisting us in monitoring the health of the animals.”

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Watch Kiki’s Ultrasound