Fetal Macrosomia: Description, Causes and Risk Factors:Fetal macrosomia is a term used to describe a newborn who's significantly larger than average.A baby diagnosed with fetal macrosomia has a birth weight of more than 8 pounds, 13 ounces (4,000 grams), regardless of his or her gestational age. About 9 percent of babies born worldwide weigh more than 8 pounds, 13 ounces. However, the risks associated with fetal macrosomia increase greatly when birth weight is more than 9 pounds 15 ounces (4500 grams).Fetal macrosomia makes vaginal delivery difficult and puts the baby at risk of injury during birth. Fetal macrosomia also puts the baby at increased risk of health problems after birth.Causes for fetal macrosomia include factors that contribute to excessive fetal growth and weight gain.Diabetes that is poorly controlled in pregnancy is the greatest risk factor for fetal macrosomia. This is believed to be partially explained by excessive growth due to elevated maternal plasma glucose levels and resulting elevated insulin and insulinlike growth factor levels, which stimulate glycogen synthesis, fat deposition, and fetal growth.
Excessive maternal weight gain and/or prepregnancy weight also play the some role in macrosomia by providing excessive growth in selected cases. Whether this is also due to undiagnosed glucose intolerance in these individuals remains to be studied.
Genetic factors also contribute to fetal size. Taller and heavier parents typically produce larger offspring.
Risk Factors:Maternal age. Women older than 35 are more likely to have a baby diagnosed with fetal macrosomia.
Maternal diabetes. If you had diabetes before pregnancy (pre-gestational diabetes) or develop diabetes during pregnancy (gestational diabetes), fetal macrosomia is more likely. If your diabetes is poorly controlled, your baby is likely to have larger shoulders and greater amounts of body fat than would a baby whose mother doesn't have diabetes.
A history of fetal macrosomia. If you've previously given birth to a baby diagnosed with fetal macrosomia, you're at increased risk of having another baby who has the condition. Also, if you weighed more than 8 pounds, 13 ounces at birth, you're more likely to have a large baby.
Maternal obesity. Fetal macrosomia is more likely if you're obese.
Excessive weight gain during pregnancy. Gaining too much weight during pregnancy increases the risk of fetal macrosomia.
Previous pregnancies. The risk of fetal macrosomia increases with each pregnancy. Up to the fifth pregnancy, the average birth weight for each successive pregnancy typically increases by up to about 4 ounces (120 grams).
You're having a boy. Male infants typically weigh slightly more than female infants. Most babies who weigh more than 9 pounds, 15 ounces (4,500 grams) are male.
Overdue pregnancy. If your pregnancy continues by more than two weeks past your due date, your baby is at increased risk of fetal macrosomia.
Variation in the percentage of fetal macrosomia in different ethnic groups has been observed independent of diabetes. In general, Hispanic women have a larger proportion of macrosomic newborns compared with white, African American, or Asian women.Symptoms:Fetal macrosomia is difficult to detect and diagnose during pregnancy. Possible signs and symptoms include:Large fundal height. During prenatal visits, your health care provider might measure your fundal height — the distance from the top of your uterus to your pubic bone. A fundal height that measures larger than expected could be a sign of fetal macrosomia.
Excessive amniotic fluid (polyhydramnios). Too much amniotic fluid — the fluid that surrounds and protects a baby during pregnancy — might be a sign that your baby is larger than average. The amount of amniotic fluid reflects your baby's urine output, and a larger baby produces more urine. Some conditions that increase a baby's size might also increase his or her urine output.
Diagnosis:Estimating or predicting a baby's birth weight is difficult. A definitive diagnosis of fetal macrosomia could not be made until after the baby is born and weighed. If you have risk factors for fetal macrosomia, however, your health care provider will likely try to estimate your baby's birth weight before delivery.Toward the end of your third trimester, your health care provider or another member of your health care team might do an ultrasound to take measurements of parts of your baby's body, such as the head, abdomen and femur. Your health care provider will then plug these measurements into a formula to estimate your baby's weight.Keep in mind that any assessment of a baby's size during pregnancy depends on accurate knowledge of his or her gestational age. If a baby is large for his or her gestational age, it is important to confirm whether your projected due date is correct.If your health care provider suspects fetal macrosomia, he or she might use nonstress testing to monitor your baby's well-being. A nonstress test measures the baby's heart rate in response to his or her own movements. If your baby's excess growth is thought to be the result of a maternal condition, your health care provider might recommend two nonstress tests each week — starting as early as week 32 of pregnancy.Before your baby is born, you might also consider consulting a pediatrician who has expertise in treating babies diagnosed with fetal macrosomia.A glucose tolerance test at 24-28 weeks of gestation screens for gestational diabetes. Early glucose screening is necessary for women with risk factors for the development of diabetes (eg, obesity, strong family history of diabetes, prior pregnancy affected by macrosomia or gestational diabetes).Imaging: Ultrasonographic measurements to obtain estimated fetal weights are indicated when clinical assessments indicate a uterine size greater than that expected for the gestational age. An examination within 1-2 weeks of delivery showing an abdominal circumference of 35 cm or larger should alert the clinician to anticipate a fetus with a birth weight of 4000 g or more. The definitive diagnosis can only be made after delivery of the neonate. Ultrasonography of the fetus and its size can be useful for identifying macrosomic infants.Treatment:If your health care provider suspects fetal macrosomia, a vaginal delivery is not necessarily out of the question. However, you will need to give birth in a hospital — in case forceps or a vacuum device are needed during delivery or a C-section becomes necessary.Inducing labor — stimulating uterine contractions before labor begins on its own — is not generally recommended. Research suggests that labor induction doesn't reduce the risk of complications related to fetal macrosomia and might increase the need for a C-section.If your health care provider recommends an elective C-section, be sure to discuss the risks and benefits. If your health care provider recommends a C-section before week 39 of pregnancy, he or she will test a sample of amniotic fluid — which surrounds and protects your baby during pregnancy — to determine whether your baby's lungs are mature enough for birth (maturity amniocentesis).After your baby is born, he or she will likely be examined for signs of birth injuries, abnormally low blood sugar (hypoglycemia) and a blood disorder that affects the red blood cell count (polycythemia). He or she might need special care in the hospital's neonatal intensive care unit. Keep in mind that your baby might be at risk of childhood obesity and insulin resistance and should be monitored for these conditions during future checkups.Also, if you have not previously been diagnosed with diabetes, after childbirth your health care provider will test you for the condition. During future pregnancies, you will be closely monitored for signs and symptoms of gestational diabetes — a type of diabetes that develops during pregnancy.NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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