Women's Healthcare Topics

Large for Gestational Age

Reviewed by James Brann, M.D.

Is Your Baby Big?

Infants who are born “big” or large for gestational age (LGA), are at risk for complications during and immediately after birth.

The definition of Large for Gestational Age is a birth weight of your baby that is greater than 90 percent of babies born at a similar age. For example, if your baby was born on their due date at 40 weeks and was in the 90th percentile your baby would weigh greater than 4000 grams or 8 lbs-8 ounces.

In contrast babies born on their due date at 40 weeks of gestation and who are appropriate for gestational age (AGA) have birth weights between 2500 grams or 5lbs-5 ounces and 3999 grams or 8lbs-7oucnes.

LGA infants are more likely to be delivered to mothers who are obese, have diabetes, and those with pregnancy weight gain greater than 40 lbs. These maternal conditions result in excessive amounts of nutrients transferred to the fetus that contributes to increased fetal weight.

Large for Gestational Age and Complications

The larger the baby the more complications for both mom and baby are seen. Maternal complications includes an increased likelihood of cesarean delivery, severe postpartum hemorrhage, and vaginal lacerations.

Baby complications are as follows:

  • Compared to AGA infants, the risk of birth injuries is twofold.
  • Increased chance of your baby being supported by mechanical ventilation for 30 minutes or more increases 2 times.
  • Increased risk of the five-minute Apgar score being lower than three.
  • The risk of respiratory distress syndrome (referred to as hyaline membrane disease) is increased.
  • The risk of meconium aspiration is greater for LGA infants.
  • Higher admission to the neonatal intensive care unit when compared with AGA infants.
  • LGA predisposes the baby to birth trauma, of which the shoulder injury is the most common, including brachial plexus nerve damage and clavicle fracture.  Hypoglycemia or low blood sugar.
  • Increase risk for perinatal asphyxia requiring oxygen support.
  • Twofold increased risk of deaths in term infants with birth weights greater than the 97th percentile or 4400 grams ( 9 pounds – 7 ounces) compared with AGA term infants.

How do You Know if Your Baby is Growing Big

From 20 weeks pregnant until you deliver, your doctor will be using a measuring tape to measure your belly at each of your prenatal visits. While this may look strange, there is a purpose – your healthcare provider is measuring your "fundal height" to assess the size of your baby.

What is the Fundal Height Measurement?

Fundal height measurement is a tool that allows your caregiver to assess your baby's growth rate and size. The fundal height is the distance from the public symphysis (or your pubic bone) to the top of the uterus. This measurement was used in the past before ultrasounds were routinely used. Today, ultrasounds and fundal height measurements are used together to monitor the baby's growth rate and size.

In general, the fundal height closely matches your pregnancy week or baby’s gestational age. For example, if you are 25 weeks pregnant, your fundal height should be around 25 centimeters, give or take a centimeter or two.

Some women measure "large for dates." This basically means that their fundal height is two centimeters longer than expected for that specific week of pregnancy. When the fundal height doesn't match up with your pregnancy week, your caregiver will schedule an ultrasound scan to find out why.

Ultrasound

Learn about a large for gestational age baby.

Ultrasound examination is the standard test to evaluate the size of your baby. The diagnosis of large for gestational age is made when ultrasound measurements of your baby’s estimated fetal weight is predicated to be above the 90th percentile for growth. Ultrasound examination to assess your baby’s weight typically involves measurement of the head diameter, head circumference and leg bone length (femur).

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