The femur bone's connected to the ... due date

A femur, or thigh bone, is the longest and strongest bone in the human body. Orangutans, who share about 94 percent of their DNA with humans, also have femur bones. When Ibu received ultrasounds, the El Paso Zoo veterinary staff was able to take femur measurements from the sonogram pictures. From the femur, the staff predicted Ibu’s due date.

Dr. Misty Garcia looks at the sonograms (and so does Ibu!) 

while Dr. Victoria Milne uses the ultrasound probe on Ibu’s belly.

Using these images and the limited data available, the vet staff made their best prediction on a due date for Ibu. Similarly to other zoos, the baby was earlier than expected. This is because compiling the data for a gestational growth curve is an ongoing process – one that the El Paso Zoo, using the baby’s data, hopes to contribute to for future births.

When a human mommy-to-be goes for an ultrasound, fetal biometry, or baby measurements, are taken from the sonogram pictures to determine the gestational and age and to assess the fetal size. These measurements generally include:

BPD, biparietal diameter, the diameter of your baby's head;

HC, head circumference, the length going around your baby's head;

CRL, (crown-rump length, the length from the top of the head to your baby's bottom;

AC, (abdominal circumference), the length going around your baby's belly and;

FL, (femur length), the length of a bone in your baby's leg.

Zoo veterinarian Dr. Victoria Milne said while these numbers have not been complied for orangutans, measurements taken here will contribute to the data for future growth curve measurements. Having these measurements helped the staff determine when Ibu would give birth to her baby orangutan. Based on the size of Ibu and Butch’s baby’s femur, the veterinary staff estimated the baby would be born in late May. This was based on the data available from other orangutan sonogram measurements. The El Paso Zoo vet staff does “awake” ultrasounds. Ibu liked watching the sonogram pictures appear on screen while the vet staff examined her.

While hundreds of thousands of human fetuses have been measured using ultrasound technology, comparatively, very few orangutan fetuses have been measured. This is in part because only orangutans in the care of humans have full medical monitoring during their pregnancy and because not all veterinary staffs have the necessary equipment to collect but also because orangutan births are so special and rare.

Dr. Brittany Rizzo at the Toledo Zoo in Ohio began collecting ultrasound data in January 2014 with the approval of the Association of Zoos and Aquariums Orangutan Species Survival Plan (SSP) after the zoo staff in Toledo also had an orangutan baby arrive a month earlier than predicted. Dr. Rizzo said creating a better orangutan growth curve is long-term project. She believes it will probably take at least a decade to get the necessary data to accurately predict orangutan baby due dates. The project is collecting the same measurements in sonogram pictures for orangutans that we have for human babies: BPD, HC, CRL, AC, and FL.

An average of 15 baby Sumatran orangutans are born each year in zoos worldwide. According to the AZA Orangutan SSP, in order to preserve biological diversity, there should be five orangutan births in AZA-accredited institutions annually. There were three births in 2014, including the one in Toledo. Ibu and Butch's baby is the second one born this year. 

Sumatran orangutans are classified as critically endangered by IUCN, the World Conservation Union. Orangutans were found in forests across Sumatra in Indonesia, but now only survive in two providences where one of their greatest threats to survival is habitat loss. Oranguntans are the only great apes found in the wild today outside of Africa.