This post was updated April 4 at 9:07 p.m.

Obstetricians at the Harbor-UCLA Medical Center found that while second-year residents are more accurate than first-year residents in estimating fetal weight, first-year residents are also capable of estimating within 10% of the true weight.

The study, published in February, compared first and second-year obstetrics residents’ ability to estimate fetal weight using two different procedures. Because residents are some of the first doctors with whom patients interact, it is critical for them to be able to provide accurate estimates, said Dr. Kimberly Huynh, a third-year OB-GYN resident at Harbor-UCLA and a co-author of the study.

“Especially at teaching institutions, the residents are the first line of health care that these patients interact with,” Huynh said. “It’s really important that our residents know how to do accurate fetal weights.”

Knowing fetal weight is helpful during the delivery process, said Dr. Hindi Stohl, the study’s senior author. If babies are larger, obstetricians might recommend a C-section rather than vaginal birth, whereas for smaller babies, obstetricians might prepare for more delivery room support or choose not to use certain devices, Stohl added.

In the study, 35 first and second-year residents each estimated the fetal weight of 10 preterm and 10 term patients each year, evaluating a total of 434 preterm and 693 term patients. The residents used two different methods depending on the patient’s weeks of pregnancy, said Dr. Alicia Lunardhi, a first-year OB-GYN resident at Harbor-UCLA and a co-author of the study.

For term patients who are over 37 weeks pregnant, residents used an ultrasound in combination with Leopold’s maneuver – a method in which physicians use their hands to measure the position and weight of the fetus, Lunardhi said. For preterm patients who are between 24 to 37 weeks of pregnancy, residents used ultrasound because the fetus is too small to be measured by hand, she said.

The actual birth weight was then recorded for babies born within two weeks of estimation and compared to the residents’ measurements, Stohl said.

Though the data was collected several years ago, it was not thoroughly analyzed until Huynh and Lunardhi discovered it. Huynh said the data caught her eye because it focused on improving residents’ education.

“We’re training future OB-GYN providers, and trying to help optimize their education as much as possible felt really important to me,” Huynh said.

The researchers also identified variables that could have affected the residents’ estimations of fetal weight, such as maternal age, past pregnancies and births, and the mother’s body mass index, Huynh said. She added that an increase in maternal BMI led to a decrease in accuracy of the estimations.

The researchers also found that there were no significant differences in accuracy between the two methods tested. This indicates that residents early in their training can estimate fetal weight accurately for both term and preterm patients, according to the study.

The research is especially important for Harbor-UCLA, which Huynh said is a safety net hospital for the surrounding community. Many patients at Harbor-UCLA do not have regular access to care, meaning they often enter care close to their delivery date, Huynh said.

One limitation of the study was that it had a relatively small sample size because of the limited size of the hospital’s OB-GYN program, said Stohl, who is also the associate program director of the OB-GYN residency program at Harbor-UCLA.

Additionally, since residents performed estimations on patients in a real-life clinical setting, researchers could not control for differences among patients, Huynh said.

Stohl said she hopes the research encourages other academic hospitals to assess their trainees’ performances in estimating fetal weight. Future studies can also include third- and fourth-year residents to observe overall trends across a residency, Huynh added.

“It’s (Fetal weight estimation is) definitely something that we want to make sure our residents are proficient in prior to graduation, both for the sake of our current patients that they’re taking care of at Harbor-UCLA and also for the sake of their future patients once they graduate,” Stohl said.