00:55 - Source: CNN
Officers rush toward choking baby in mall
choking baby mall deputies save newsource orig_00004509.jpg
Clackamas County Sheriff's Office
choking baby mall deputies save newsource orig_00004509.jpg
Now playing
00:55
Officers rush toward choking baby in mall
CNN; USACW Hospital; Molli Potter
Now playing
01:06
Hospital hosts graduation for NICU baby
nurses pregnant arizona hospital dnt vpx_00000202.jpg
nurses pregnant arizona hospital dnt vpx_00000202.jpg
Now playing
00:55
16 Arizona nurses pregnant at same hospital
Packer Family Photography
Now playing
00:44
Photo of baby encircled by IVF needles goes viral
AUCKLAND, NEW ZEALAND - JUNE 24:  New Zealand Prime Minister Jacinda Ardern and partner Clarke Gayford pose for a photo with their new baby girl Neve Te Aroha Ardern Gayford on June 24, 2018 in Auckland, New Zealand. Prime Minister Ardern is the second world leader to give birth in office, and the first elected leader to take maternity leave. Arden will take six weeks of leave with Deputy Prime Minister Winston Peters assuming the role of Acting Prime Minister  (Photo by Fiona Goodall/Getty Images)
Fiona Goodall/Getty Images AsiaPac
AUCKLAND, NEW ZEALAND - JUNE 24: New Zealand Prime Minister Jacinda Ardern and partner Clarke Gayford pose for a photo with their new baby girl Neve Te Aroha Ardern Gayford on June 24, 2018 in Auckland, New Zealand. Prime Minister Ardern is the second world leader to give birth in office, and the first elected leader to take maternity leave. Arden will take six weeks of leave with Deputy Prime Minister Winston Peters assuming the role of Acting Prime Minister (Photo by Fiona Goodall/Getty Images)
Now playing
01:09
New Zealand prime minister gives birth
jason biggs baby meets eugene levy
Jason Biggs
jason biggs baby meets eugene levy
Now playing
01:05
Jason Biggs introduces baby to movie dad
Courtesy Cleveland Clinic News Service
Now playing
00:36
Doctor delivers baby 35,000 feet in the air
Now playing
00:59
Couple's announcement stuns grandma
Now playing
01:01
Troops reveal gender of fallen soldier's baby
Skype
Now playing
02:37
Baby born from embryo frozen 25 years ago
australia large baby born dnt_00002723.jpg
Seven Network
australia large baby born dnt_00002723.jpg
Now playing
01:16
One of Australia's biggest babies
Now playing
02:14
Baby girl arrives early, so dad did this ...
The Cebu Pacific crew on duty during the birth
Courtesy Cebu Pacific
The Cebu Pacific crew on duty during the birth
Now playing
01:12
Baby born on plane gets 1M air miles
ultrasound image jesus crucifixion pkg_00001221.jpg
WFIE
ultrasound image jesus crucifixion pkg_00001221.jpg
Now playing
01:02
Mom-to-be was shocked to see THIS ...
47 year old pregnant didnt know pkg_00002610.jpg
WCVB
47 year old pregnant didnt know pkg_00002610.jpg
Now playing
01:39
Woman goes to ER with stomach pain, delivers baby
Now playing
00:59
NYPD officer delivers baby during rush hour

Story highlights

Only 5% of pregnant women deliver on their estimated due date

Predicting labor is a tough thing for doctors to do

(CNN) —  

Of all the pregnant women you’ve known in your life, how many delivered their precious bundle of joy on their due date?

Probably not many. Only 5% of pregnant women deliver on their estimated due date, with most celebrating baby’s arrival one to three weeks early or late. But a new meta-analysis from Thomas Jefferson University in Philadelphia says a routine test might help moms late in pregnancy narrow the window when baby is expected.

“Measuring cervical length via ultrasound at around 37-39 weeks can give us a better sense of whether a mother will deliver soon or not,” Dr. Vincenzo Berghella, a senior author of the analysis, said in a press release.

The study analyzed the use of transvaginal ultrasound measurements of cervical length for 735 women with single-child term pregnancies and found when the cervix was 10 millimeters or less, there was an 85% chance the baby would be born within the next seven days. When the cervix was less than 30 millimeters, there was a 50% chance.

“Women always ask for a better sense of their delivery date in order to help them prepare for work leave, or to make contingency plans for sibling-care during labor,” said Berghella, who is director of maternal fetal medicine at Thomas Jefferson University Hospital. “These are plans which help reduce a woman’s anxiety about the onset of labor,” allow “providers and birth locals” to better plan staff and coverage, and help women decide if they should go with repeat caesarean delivery or attempt vaginal birth.

Doctors contacted by CNN weren’t so sure about the study’s conclusions.

“This seems more like a party trick, rather than a useful tool,” said Dr. Katie Babaliaros, an OB-GYN with Peachtree Women’s Specialists in Atlanta. “At the very best, there’s still 15% of these women who are going to be saying ‘Where’s my baby?’”

“Checking a cervical length at term only gives a window of time, in weeks, in which a woman may deliver,” said Dr. Dian Tossy Fogle, a perinatologist at Northside Hospital Center for Perinatal Medicine in Atlanta. “Most patients are already prepared that delivery will be occurring in the near future and have taken precautions. I do not see a real use for this in daily clinical care.”

How due dates are determined

To determine a due date, doctors use a simple calculation using the first day of a woman’s last menstrual period. They then add 280 days to get to what would be considered a “term” baby: 40 weeks of gestation.

“This can be confirmed, ideally, by a first trimester ultrasound,” Fogle said. “If the menstrual period is unknown, then an ultrasound may be performed to establish a due date. First trimester ultrasounds are very accurate in determining the due date.”

The problem with knowing if baby will actually be born on that due date is that science isn’t sure about all the reasons why a woman goes into labor.

“There are many factors that are unknown and beyond the control of women or the best medical experts that will predict when a baby will deliver,” said Dr. Pratima Gupta from Physicians for Reproductive Health.

“We just don’t know how all the pieces all fit together,” Babaliaros said. “In the weeks leading up to delivery, there are a ton of hormones and chemicals that are released by the mom and the baby to trigger labor and those occur in very complicated ways.”

Potential downsides to ultrasounds

To further burst the bubble of women hoping for a more accurate delivery date, the experts CNN talked to mentioned several downsides to transvaginal ultrasounds.

“My concern with this study is that it will increase health care costs with no clinical benefit,” Fogle said. “If the goal is to reduce ‘maternal anxiety’ regarding timing of delivery, a simple physical exam of the cervix performed at a routine OB visit can also give a patient an idea of how soon they will deliver.”

The transvaginal ultrasound also won’t necessarily produce a more accurate measurement, experts said.

“Cervical length measurement can vary depending on the provider performing it,” Gupta said of the ultrasounds. “Therefore, the potential downside to this new technique is that a woman is given an (estimated due date) that is inaccurate due to the subjectivity of who did the measurement.”

Fetal medicine specialist Dr. Ashley Roman, director of the division of maternal fetal medicine at NYU Langone Medical Center, said it might be helpful for some patients with rare planning needs.

“The patient who has a partner who is traveling out of town or who is serving abroad in the military,” Roman said. “If the cervical length is less than 10 millimeters, it might be time to hang around.”

“But even if the cervical length is greater than 30 millimeters, the chance of delivering in the next week is like flipping a coin. ‘Who knows?’ This data isn’t that helpful because this is what we already tell our patients.”