Fetal macrosomia is a term used when your baby is born at a much larger than average birth weight. Average birth weight for a baby is 7 pounds. Macrosomia means large body. Babies who are diagnosed with fetal macrosomia weigh 8 pounds, 13 ounces or more than 9 pounds, 15 ounces. About 9% of babies born worldwide weigh more than 9 pounds, 15 ounces.
Complications
Having a big baby can lead to complications during delivery. There is an increased risk to the mother of sustaining injury to the birth canal, genital tract, or perineum. There is also a risk of postpartum hemorrhage, or a uterine rupture. Long labors are more common with babies that are larger.
Your baby is at risk of complications as well. Your baby’s heart rate may change or fluctuate due to the long labor or the increased stress of them being so large. Shoulder dystocia is the most common one. This is when the baby gets stuck in the birth canal. The baby’s shoulder gets stuck under the pubic bone. It can cause the doctors and nurses to do some maneuvering or to perform an episiotomy to allow space for the baby to come out. Shoulder dystocia can cause bone fractures to the baby, either their clavicle or their upper arm, a brachial plexus injury, or brain damage. Your baby is at higher risk of having high red blood cell counts which can lead to jaundice. Your baby may also be at risk of having low blood sugar, or breathing problems.
In the future fetal macrosomia puts them at higher risk for developing diabetes, insulin resistance, or metabolic syndrome.
Signs & Risks
It can be hard to know if your baby will be born larger than average. Pregnancy symptoms can feel the same regardless of the size of your baby.
One of the signs your doctor may first notice is that your fundal height measures larger than how many weeks you are pregnant. The fundal height is the measurement from the top of the pubic bone to the top of the uterus. It is usually equal in centimeters to the week you are pregnant. At 28 weeks, a normal fundal height would measure 28 centimeters. A large baby may be measuring a fundal height of one to two weeks ahead.
If you have gone past your due date you are at a higher risk of having a large baby.
Too much amniotic fluid can also be a sign your baby is large.
If you started off the pregnancy obese, or have gained a lot of weight during pregnancy, that can also be a sign your baby is large.
Having diabetes prior to being pregnant, or developing gestational diabetes can also lead to fetal macrosomia.
If you have had a previous pregnancy and delivered a large baby you are at a higher risk of having another large baby. Usually each pregnancy the babies will weigh about 4 ounces heavier than the previous one.
Caring a boy can also raise your risk of fetal macrosomia.
Tests & Procedures
Around 34 weeks your doctor will suggest doing growth ultrasounds if they suspect your baby may be larger than normal. These ultrasounds will help the doctors estimate what your baby’s weight will be at birth. Ultrasounds are not entirely accurate. They can be off as much as 10% in estimating the weight of your baby. Meaning if the ultrasound estimates your baby is 9 pounds, your baby really could weigh anywhere between 8 to 10 pounds. An ultrasound cannot predict shoulder dystocia.
Depending on your doctor they may want to monitor the baby another way. They may suggest undergoing some non stress tests to measure the baby’s heart rate and how it responds to his or her own movement. A non stress test can help monitor the baby’s movements, tone, breathing, and the volume of amniotic fluid.
Delivery
Fetal macrosomia does not mean that a vaginal delivery is out of the question. You still may be able to deliver vaginally. Speak with your doctor on how you would navigate different complications with a vaginal delivery. Your doctor may recommend you have a c section delivery if you have diabetes or gestational diabetes, your baby is estimated to weigh more than 11 pounds, or you have delivered a baby previously whose shoulder got stuck. You are at a higher risk of shoulder dystocia happening again if it happened previously.
Your baby cannot be actually diagnosed with fetal macrosomia until after they are born. Your doctor may be more aware of the possibility if you had previous pregnancies where the baby has fetal macrosomia. Fetal macrosomia does cause there to be more complications possible for mother and baby during delivery. Most babies are born healthy.
READ MORE: I’m Pregnant: What to Expect and How to Prepare
Sources:
https://www.babycenter.com/pregnancy/your-body/macrosomia_1152319
https://www.mayoclinic.org/diseases-conditions/fetal-macrosomia/diagnosis-treatment/drc-20372584
https://my.clevelandclinic.org/health/diseases/17795-fetal-macrosomia
https://www.webmd.com/baby/what-is-fetal-macrosomia