A baby that weighs more than 8 lbs 13 ounces at the time of delivery is considered a "macrosomic" or "large for gestational age" baby. There are certainly women delivering all over the world that are able to deliver these larger babies vaginally. The issue with large babies, however, is two-fold. There are maternal issues (potential problems for mom) and fetal issues (potential problems for baby). Let's talk about issues that can affect moms first. There is automatically an increased risk of needing a C-section once in labor. This is because women with larger babies have longer labors and an increased risk of not having the cervix dilate fully or not having the fetus' head drop down. There is also an increased risk of trauma to the vagina and surrounding areas, including an increased risk of a 4th degree laceration (a tear that extends into the rectum). There is an increased risk of something called shoulder dystocia. This occurs when a baby's head is delivered, but his or her shoulder gets stuck behind mom's pubic bone. In fact, in baby's estimated to be over 10 lbs, there is a 10-fold increased risk of this happening. Lastly, there is an increased risk of postpartum hemorrhage (excessive bleeding after delivery).
Now let's take a look at the risks to baby. As mentioned above, shoulder dystocia can be very dangerous for babies. It can lead to nerve damage in the baby's shoulder and arm, a clavicular fracture (broken collar bone), lower Apgar scores once born and fetal death. There is also an increased risk of having the baby spend some time in the NICU (neonatal intensive care unit).
It is because of these risks that women who are carrying fetuses suspected to be over 10 pounds (if diabetic) and over 11 pounds (if not diabetic) are offered a C-section. Many women who are planning on a vaginal delivery or a natural birth often have a wrench thrown into the plan when a condition arises that could be dangerous for mom or baby. Ultimately, at the end of everything, the goal is a healthy mom and a healthy baby. Talk to your doctor about your concerns and if you are completely aware of all the risks and benefits of both delivery modes, then you will be making an educated decision for you and your unborn child.