“Big Babies” Don’t Always Need a C-Section Delivery

Case: A 28-year old G1 P0 (first pregnancy, no prior births) at 39 weeks is thought to have a large baby. The ultrasound estimated fetal weight (EFW) is 9 lbs. The patient was considered overweight with a BMI of 29 and the total weight gain during pregnancy of 45 lbs. The patient’s glucose screen was negative. The physician recommended a primary Cesarean delivery because the baby was “big” and the mother will most likely end up with a Cesarean regardless. At delivery the baby weighted 7 pounds, 8 ounces. Three days later, the mother developed a fever and wound infection that required an opening of the entire incision. The mother was on IV antibiotics for 72 hours and then sent home six days after giving birth with a wound vacuum. At four weeks post-discharge, the wound was finally closed.

In a review of nearly 1,400 Cesarean delivery event reports in the perinatal category of the CHPSO database, cases like the one mentioned above represent about one third of the identified causes of inappropriate Cesarean delivery: deviation from the standard of care. The mother’s BMI at 29 is not necessarily high and the baby was misdiagnosed as being macrosomic. Babies may be diagnosed with fetal macrosomia, literally “big body” if they are known to weigh 8 pounds, 13 ounces (4,000 grams) or more. The case above illustrates the controversy of performing a Cesarean delivery on a mother with a relatively low BMI and a fetal weight via ultrasound that was borderline. There was no mention of a trial of labor. A recent study found that women who attempted vaginal delivery at term, Cesarean delivery was likely when the estimated fetal weight was documented either clinically or via ultrasonography. The relationship was strongest at higher fetal weight estimates.

Estimating fetal weight via ultrasound is not very reliable. The American College of Obstetricians and Gynecologists issued the following guidelines.

Recommendations based on good and consistent scientific evidence (Level A):

  • The diagnosis of fetal macrosomia is imprecise. For suspected fetal macrosomia, the accuracy of estimated fetal weight using ultrasound biometry is no better than that obtained with clinical palpation (Leopold’s maneuvers).

Recommendations based on limited or inconsistent scientific evidence (Level B):

  • Suspected fetal macrosomia is not an indication for induction of labor, because induction does not improve maternal or fetal outcomes.
  • Labor and vaginal delivery are not contraindicated for women with estimated fetal weights up to 5,000 g in the absence of maternal diabetes.
  • With an estimated fetal weight more than 4,500 g, a prolonged second stage of labor or arrest of descent in the second stage is an indication for cesarean delivery.

Recommendations based primarily on consensus and expert opinion (Level C):

  • Although the diagnosis of fetal macrosomia is imprecise, prophylactic cesarean delivery may be considered for suspected fetal macrosomia with estimated fetal weights of more than 5,000 g in pregnant women without diabetes and more than 4,500 g in pregnant women with diabetes.
  • Suspected fetal macrosomia is not a contraindication to attempted vaginal birth after a previous cesarean delivery.
  • Although the risk of birth injury from vaginal delivery rises with increased birth weight, vaginal delivery is not contraindicated in pregnant women with estimated fetal weights up to eleven pounds, as long as the pregnancy is not complicated by diabetes.

As there are risks involved in both Cesarean delivery and induction, open communication with medical staff and the mother must not be overlooked.

The California Maternal Quality Care Collaborative has had an overwhelming response from hospitals interested in participating in the Collaborative to Support Vaginal Birth and Reduce Primary Cesareans. If your California hospital has an NTSV rate greater than 23.9 percent (the Healthy People 2020 goal) and are not currently participating but would like to, please send an email to

A webinar on trends in CHPSO perinatal event data, and successes of small rural hospitals in achieving the Healthy People 2020 goal will take place on April 20 at 12:00 pm PDT. To register, click here.


Chatfield, J. ACOG Issues Guidelines on Fetal Macrosomia. Am Fam Physician. 2001 Jul 1;64(1):169-170.

Froelich RJ et al. Association of Recorded Estimated Fetal Weight and Cesarean Delivery in Attempted Vaginal Delivery at Term. Obstet Gynecol. 2016 Sep;128(3):487-94.

Fetal macrosomia definition. Mayo Clinic.