12/28/2025
BIG BABIES
Let’s talk about them. What’s evidence based and what isn’t? There’s a lot that gets discussed when a big baby is expected, but what if all of that’s useless and can cause more harm than benefit? Let’s get into it.
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This is a long post, so here’s a complete summary that’s also listed at the bottom of the Evidence Based Birth article:
-Non-Diabetic Mothers-
•Ultraounds are only right about 50% of the time. Ultrasound weight results anywhere from 15% above or below baby’s actual weight.
•7-15% of big babies will experience shoulder dystocia.
•Permanent nerve damage risk is as follows:
—> 1 in every 555 babies (0.18%) between 8lbs 13oz - 9lbs 15oz.
—> 1 in every 175 babies (0.57%) 9lbs 15oz or more.
*Regular training for shoulder dystocia is extremely important.
•Providers suspecting big babies are more harmful than the baby actually being big. This is because of the way providers manage labor with a suspected big baby that increases the risk of cesarean and complications.
•Very early induction (37-38w) can prevent some cases of shoulder dystocia, but it doesn’t show to decrease brachial plexus palsy or other risks that come with early induction.
•Elective cesarean likely does more harm than good.
-Diabetic Mothers-
•Ultrasounds are slightly more accurate.
•Providers should follow the standard definition of slow labor.
•There might be some benefit to elective cesarean with babies over 9lbs 15oz, but this is not conclusive.
•Management of diabetes such as diet, exercise, or medication lowers the chance of having a big baby or shoulder dystocia down to normal levels.
Read below for all the details!
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Macrosomia is the medical term for “big baby”. A big baby is any baby that is 4,000g or 8lbs 13oz or bigger. Some say 4500g+, or 9lbs 15oz. For most, when a big baby is referred to, they’re referring to a baby larger than 8lbs 13oz. An extremely large baby would be a baby 5,000g or more, or 11+ lbs. Large for gestation age is referring to any baby larger than the 90th percentile at birth. This means that there are only 10% of babies that are larger.
Risk factors that can contribute to a big baby are:
•Big babies in families (genetics)
•Male baby
•Higher BMI before pregnancy
•Older age
•Post term
•Previous big baby
*Exercise has been shown to decrease the risk of a large baby.
-Routine Care For Suspected Big Baby-
Only 1 in 10 babies are born large, but in one study 2 out of 3 families were told they could expect a large baby. In the end, the average weight was only 7lbs 13oz. Two of three mothers had discussions with their provider about induction, and one of three had discussed a planned cesarean simply due to suspicions of a large baby. 67% were induced and 37% tried self-induction. One in five were not even offered a choice when it came to induction. One in three went with a planned cesarean, and two of five respondents said their discussion was framed that cesarean was the only option. Not only is this incorrect, but it majorly lacks informed consent.
“Big baby” concerns were the 4th most common reason for induction, and the 5th most common reason for cesarean.
Is cesarean or induction even evidence based for suspected large babies? This approach is based off these 5 assumptions:
•Higher risk of shoulder dystocia
•Higher risk of birth problems
•Providers can accurately tell baby’s size
•Induction keeps baby from getting bigger; therefore, decreasing risks.
•Elective cesareans are only beneficial IF they don’t have major risks that could outweigh the benefits
-ASSUMPTION #1: SHOULDER DYSTOCIA-
Truth: 7-15% of large babies will have issues with birth of their shoulders. Most are handled without harm. Permanent nerve damage happens in 1 out of every 555 babies, (0.18%), between 8lbs 13oz and 9lbs 15oz, and 1 out of 175 in babies, (0.57%), over 9lbs 15oz or larger.
Providers get nervous of large babies because the possible risk of nerve damage. Brachial plexus palsy is the most common cause of litigation.
A combination of multiple studies found that shoulder dystocia happened to 6% of babies over 8lbs 13oz, and 0.6% who were not “big”. The risk raised to 14% for those 9lbs 15oz or larger.
Rates were higher in those with Type I or II diabetes. 2.2% that were less than 8lbs 13oz, 13.9% that were 8lbs 13oz - 9lbs 15oz, and 52.5% that were over 9lbs 15oz. Treatment and management of gestational diabetes drastically reduced the chance of having a large baby with dystocia. Mothers with high blood sugars during pregnancy are at an increased risk for shoulder dystocia even when baby is not big because weight can be distributed differently on baby. Problems are mostly likely to occur when baby’s head is smaller in comparison to their shoulders and abdomen. Half of all dystocias occur in a baby who is NOT big. Shoulder dystocia can NOT be predicted. This is why ALL providers must know how to accurately diagnose dystocia and quickly and effectively manage it.
-Brachial Plexus Palsy-
Brachial plexus palsy refers to weakness or paralysis of an arm, shoulder, or hand. This happens to 1.3 out of every 1,000 (0.13%) of all vaginal births. This can occur with or without dystocia being present. 48-72% of BPP cases happen without dystocia. Rarely, this can happen during a cesarean. In a study with 387 children who experienced BPP, 92% were born vaginally and 8% by cesarean. Other researched have found it occurs in 3 per 10,000 cesareans, (0.03%). About 10-18% end up with permanent injury, defined as arm or shoulder weakness after 1 year.
After combing 5 studies, babies over 8lbs 13oz vs babies who were not born big had significantly more brachial plexus palsy injury, (0.74% vs 0.06%). The rate increased to 1.9% for babies over 9lbs 15oz. In a recent study, extremely large babies (over 11lbs), 17 out of 120, (14.2%) experienced shoulder dystocia. 3 out of 17, (17.6%) had temporary brachial plexus palsy, but were healed within 6 months. The overall rate was about 1 BPP cases happen per 40 vaginal births, (2.5%), when baby is 11lbs or larger.
-Can A Baby Die From Shoulder Dystocia?-
Yes, it’s possible, but it’s rare. Out of 15 studies, there were 0 deaths to of 1,100 cases. Two other studies showed 1%* and 2.5%**.
—>*One baby out of 101 “died at delivery”, possibly due to shoulder dystocia, but not clear.
—>**One baby out of 40 cases of shoulder dystocia.
In a 2011 study, 132,098 women gave birth. 1.5% had shoulder dystocia, and of those 101 were injured, (brachial plexus palsy or collar bone fracture). There were 0 deaths and 6 cases of brain damage due to an average time of 11 minutes between birth of babies head and body.
-ASSUMPTION #2: BIG BABY LEADS TO AN INCRASED RISK OF HEALTH PROBLEMS AND COMPLICATIONS-
Truth: Risk of complications with a big baby are higher along a spectrum. So babies lower on the big baby scale have less risk and those higher have a higher risk. The same risk doesn’t apply to a 8lbs 13oz baby like it does a baby larger than 11lbs. A providers suspicion of a big baby also carries its own risks.
-Unplanned Cesareans-
In a meta-analysis, babies larger than 8lbs 13oz are more likley to end in a cesarean. The average rate was 19.3% compared to 11.2% when a baby that was not suspected to be big. With babies suspected to be over 9lbs 15oz, the unplanned cesarean rate rose to 27%. A providers suspicion can also lead to an increased risk of unplanned cesarean.
-Perineal Tears-
The largest study showed that a 3rd degree tear had a rate of 0.87% with a big baby, and 0.45% without a big baby. Forceps and vacuums were more likely to be used with big babies, and both of these increase the risk of severe tears.
-Postpartum Hemorrhage-
Mothers with babies over 8lbs 13oz had a rate of 4.7% of hemorrhage compared to 2.3% when mothers didn’t have big babies. With a baby over 9lbs 15oz, the rate was 6%. It is not clear whether the higher rate is due to the big baby or induction or cesarean that was recommended by the provider.
-Newborn Complications-
One study found that large babies had a higher rate of low blood sugar, 1.2%, compared to 0.5% when baby was not large. Larger babies had higher rates of temporary breathing issues, (1.5%), compared to those who were not large, (0.5%). Higher temp was also seen more in large babies than average sized babies, (0.6% vs 0.1%). Birth trauma was experienced at a rate of 2% for large babies rather than 0.7% of average sized babies. Lastly, there were more large babies born via cesarean (33% vs 15%). The cesarean births for larger babies could also explain the temporary breathing issues since that is a side effect to cesarean births.
A combined 5 studies shows that birth fractures occurs in 0.54% in larger babies versus 0.08% in average sized babies. This rate increases to 1.01% in babies 9lbs 15oz or larger.
-Stillbirth-
Some doctors will recommend cesareans for suspected big babies because they believe there is a higher risk of stillbirth in larger babies. A study grouped babies together in this fashion:
•4th-10th percentile
•11th-20th percentile
•21st-80th percentile
•81st-90th percentile
•91st-97th percentile
•98th-100th percentile
The group with the highest stillbirths was the smallest group. The third highest risk group for stillbirth was the 98th-100th percentile group.
—>This could be partially explained by mom being diabetic, but also a higher risk of unexplained stillbirths happen in this group as well. The group with the lowest risk of stillbirth was the 91st-97th percentile.
Another study showed several other risk factors for stillbirth, such as:
•High BMI in mom
•Smoking during pregnancy
•Older age
•High blood pressure and gestational diabetes
•Small for gestational age
*Being large for gestational age looked to be protective against stillbirth unless it was due to gestational diabetes or mom with type I or II diabetes. Remember, though, diabetes can be improved with diet and exercise which showed a drastic decrease in bad outcomes. The largest study on gestational diabetes showed NO increased risk for stillbirth. The Canadian study showed a link to stillbirth IF gestation diabetes and baby was large for gestational age were both factors.
In the largest study of more than 100 million babies, about 10% were large. There were 1.2 per 1,000, (0.12%) stillbirths for large babies compared to 1.1 per 1,000, (0.11%) for average sized babies.
Because stillbirth has many factors and varies so much from situation to situation, each pregnancy should always be individualized.
-Is It Harmful to Suspect a Big Baby?-
Suspecting a big baby leads to a higher rate of cesareans. Research consistently shows perception of a big baby is more harmful than a big baby itself. NINE different studies showed suspicion of a big baby leads to higher cesarean rates and higher diagnoses of stalled labors. Suspicion of big baby, and those who actually had one, had triple the inductions, more than triple the cesareans, and quadruple the amount of maternal complications compared to those who weren’t suspected to have a large baby but actually did. Researchers suggested a weigh cut-off of 9lbs 15oz, or larger, to trigger counseling to avoid unnecessary interventions and maternal complications.
-ASSUMPTION #3: WE CAN TELL WHICH BABIES WILL BE BIG-
Truth: Physcial exams and ultrasounds are equally bad at predicting a large baby. 14 studies looked at ultrasound reliability to predict a baby larger than 8lbs 13oz. It was accurate 15-79% of the time. Most studies showed the accuracy was less than 50%.
—> In other words, for every 10 babies, 5 will weigh more than 8lbs 13oz and 5 will weigh less.
Ultrasound was less accurate at predicting babies over 9lbs 15oz. Accuracy of extremely large babies was 22-37%.
—> In other words, for every 10 babies, 2-4 weighed more than 9lbs 15oz and 6-8 weighed less.
In women with diabetes, ultrasounds were more accurate at 44-81% accuracy.
—> In other words, for every 10 babies of mothers with diabetes, 6 will weigh more than 8lbs 13oz and 4 will weigh less.
Over all, when there is a suspicion of a large baby, there is only a 40-53% accuracy.
—> In other words, half will weigh more than 8lbs 13oz and half will weigh less.
A systematic review concluded: “No clear consensus with regard to prenatal identification, prediction, and management of macrosomia”. The authors also stated that macrosomia can only be diagnosed AFTER birth.
The Warsof2 formula, which goes by abdominal measurements, came within 15% of baby’s true weight.
-ASSUMPTION #4: INDUCTION ALLOWS BABY TO BE BORN AT A SMALLER WEIGHT, WHICH HELPS AVOID DYSTOCIA AND LOWERS RISK OF CESAREAN-
Truth: There is conflicting evidence about whether induction for suspected big babies can improve outcomes.
A Cochrane review split mothers into two groups. One was induced at 37-40w and the other would wait for labor to begin. The induction group had a decrease in dystocia (4.1% vs 6.8%), a decrease in fractures (0.4% vs 2%), an increase in perineal tears (2.6% vs 0.7%), and an increase in jaundice (1.1% vs 0.7%). There was no difference in cesarean, instrumental delivery or NICU admissions, brachial plexus palsy, or low APGAR. There were also 0 deaths.
The second largest study included women who were at least 38 weeks, suspected to have a big baby, (over 8lbs 13oz), no gestational diabetes, and no previous cesarean. Those results showed that women who waited for labor had babies about 5 days later, had slightly larger babies (3.5oz heavier), no dystocia difference, no nerve damage, no cesarean rate difference. Ultrasound overestimated the weight 70% of the time and under-estimated 28% of the time.
In summary, ultrasound estimates of weight was inaccurate, shoulder dystocia and nerve damage is unpredictable, and induction did not decrease cesarean or shoulder dystocia risks.
-ASSUMPTION #5: ELECTIVE CESAREAN FOR BIG BABY HAS BENEFITS THAT OUTWEIGH POTENTIAL HARMS-
Truth: Researchers have never carried out a study to determine the effects of elective cesarean for suspected big babies.
Evidence did NOT support elective cesarean as a way to prevent bad outcomes due to big babies. Some known cesarean risks are serious infections, blood clotting disorders, postpartum hemorrhage requiring transfusion, and newborn breathing problems.
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For those who have read my personal summary, thank you! You can find the entire article at: https://evidencebasedbirth.com/evidence-for-induction-or-c-section-for-big-baby/
