Hadassah research: Circumference of fetus’s head most accurate way to decide on cesarean

About five percent of fetuses are exceptionally large and are at risk of getting stuck in the birth canal.

Mother changing baby diaper (photo credit: INGIMAGE)
Mother changing baby diaper
(photo credit: INGIMAGE)
The circumference of a large fetus’s head rather than its estimated weight accurately predicts whether the mother will have to undergo a cesarean section or vacuum to delivery the baby, according to new research at the Hadassah University Medical Center in Jerusalem’s Ein Kerem.
About five percent of fetuses are exceptionally large and are at risk of getting stuck in the birth canal. Obstetricians usually say that any fetus whose estimated weight (using ultrasound) is higher than four-and-a-half kilos should be delivered by cesarean.
Hadassah obstetricians/gynecologists Prof.
Simcha Yagel, who heads Hadassah’s ob/gyn branch, and Prof. Drorith Hochner, who runs the ob/gyn department at Hadassah on Mount Scopus reexamined the criteria for a cesarean along with Prof. Yossi Ezra, head of the highrisk pregnancy inpatient department. They found that the length of the circumference of the fetus’s head was much more accurate a measure than the fetus’s weight.
“It seems that there is greater difficulty dealing with a fetus with a head larger than average who is under the 95th percentile of weight than a big baby who has a higher-percentile weight, but whose head circumference is smaller,” said Yagel.
The research team collected data on 30,000 babies born between 2010 and 2012 at the two Hadassah hospitals to identify which babies had to be delivered by Cesareans or by vacuum and compared them with various parameters.
They compared the babies’ actual weight at birth to the weight estimated when it was in the womb and the circumference of the head after birth, as well as the rate of cesareans and vacuum births.
On the basis of this data, the Hadassah physicians reached their new conclusions.
“Our research shows us that there is a good reason to change the protocol relating to a large fetus. We are now in the middle of a study examining whether the real results are correct also when we base our assessments on ultrasound scans about the head circumference and the weight of the fetus in the womb,” Yagel said.
Since the protocol affects whether one carries out a cesarean or not, many mothers could be allowed to have a natural vaginal birth that is safer both for the mother and the baby. When the team looked at cases in which using a vacuum to deliver the baby failed and a cesarean had to be performed, it turned out that the failure was three times as high if the head circumference was larger than normal. Thus, a baby’s suffering could be reduced by not using a vacuum when it is unnecessary, Yagel said.
The study has just been published in the American Journal of Gynecology and was selected as the “Editor’s Choice” for the issue. Hadassah will change its protocol on delivering large babies already this year as a result of the finding.