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If you’ve arrived at the point in your pregnancy where your doctor or midwife is talking about or measuring fundal height, congratulations — you’re more than halfway there! Let’s take a look at what exactly fundal height is, and explore reasons why a person might measure large or small.

What Is Fundal Height?

Definition

Symphysis fundal height — also called SFH or fundal height — is a measurement your healthcare provider uses to help track your baby’s growth. Early in pregnancy, your uterus is small enough to fit inside your pelvic cavity, but it expands upward as it grows. By around week twelve, the top of the uterus (the fundus) can be felt just above the pubic bone (symphysis pubis) (1). Starting midway through pregnancy, the distance from the pubic bone to the top of your uterus, in centimeters, should approximately equal your baby’s gestational age (2). For example, if you’re 25 weeks pregnant, your fundal height should be about 23 – 27 centimeters.

Tracking Baby’s Growth

By measuring your fundal height at each appointment from mid-pregnancy on, your healthcare provider can get an idea of how big your baby is and how she is growing. Over time, they use this measurement to track whether her growth is steady and progressing. For example, if your baby has been consistently in the 25th percentile, that’s a normal track for her. However, if a baby has been measuring consistently in the 80th percentile and is suddenly in the 10th percentile, your doctor may want to do additional tests to ensure that everything is okay.

When And How Is Fundal Height Measured?

Your doctor or midwife will start measuring your fundal height at around week 24, and will continue to do so at each appointment until your baby is born. This is a simple, painless measurement that will take just a few moments. You will lie on your back, and your caregiver will use a tape measure, like the ones used by seamstresses or tailors. Your provider will press gently in order to feel the top of your pubic bone and the top of your uterus, but this should not be uncomfortable for you.

You’re Measuring Large Or Small For Gestational Age

What happens if your measurement is more than two centimeters above or below your baby’s gestational age? Does it mean there’s a problem with your baby’s size or development? The good news is that your baby is still likely perfectly healthy! There are a variety of reasons why measurements may be slightly off, and most of these reasons are no cause for alarm.

Measuring Large for Gestational Age

If your fundal height is measured to be more than two centimeters above your baby’s gestational age, you will be said to be measuring large for gestational age. Here are some reasons you may measure large:

• The estimated due date is incorrect. You may be a little farther along than was originally calculated, especially if your due date was based on a missed period rather than early ultrasound.
• Your BMI is more than 30.
• You have uterine fibroids.
• Your bladder might be very full, or you may really need to have a bowel movement.
• You have a narrow pelvis.
• Your abdominal muscles are looser than average.
• The baby is in an unusual position or breech.
• You have too much amniotic fluid, a condition called polyhydramnios.
• Your baby is large. This may be a condition called macrosomia where a baby is much larger than normal. This is most common if the mother has gestational diabetes.
• Or your baby may just be perfectly healthy and larger than average (3).

Measuring Small for Gestational Age

If your fundal height is more than two centimeters smaller than your baby’s gestational age, you will be labeled as measuring small for gestational age. Here are some reasons you might measure small:

• Your due date is incorrect. You may not be quite as far along as initially estimated.
• You have well-conditioned abdominal muscles.
• Your baby has descended into your pelvis, which happens in late pregnancy.
• You have too little amniotic fluid, a condition called oligohydramnios.
• Your baby has intrauterine growth restriction, also called IUGR. This is a diagnosis given to a fetus who is below the 10th percentile for its gestational age (4).
• You may just be carrying a perfectly healthy baby who is smaller than average (3).

What’s Next If I Measure Large or Small?

If you measure large or small one time, your doctor or midwife will likely just note it and check again at the next appointment. If it seems that your baby isn’t growing the way he or she should, your provider may order additional tests. You may have an ultrasound to check on baby and measure amniotic fluid levels. You may also have more frequent appointments.

It’s important not to put too much worry into fundal height measurements. They’re a useful, yet imperfect, tool to help your healthcare provider keep track of your baby’s growth. But they are just one tool of many. Your doctor can learn a great deal in later pregnancy by palpating your abdomen to determine baby’s position and size. They may also use ultrasound, along with a variety of other tests, to get a more detailed picture of what’s going on in your uterus. So while large or small fundal height measurements may lead to increased tests, it is very likely not a cause for alarm.

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References:

1. The American College of Obstetricians and Gynecologists.  (2010).  Your Pregnancy and Childbirth Month to Month, 5th edition.
2. Simkin, P. (2010). Pregnancy, Childbirth and the Newborn, 4th edition. Meadowbrook Press
3. Miles, K., MD. (n.d.). Fundal height: Measuring large or small for gestational age. Retrieved November 16, 2020, from https://www.babycenter.com/pregnancy/health-and-safety/fundal-height-measuring-large-or-small-for-gestational-age_1453305
4. Peleg, D., Kennedy, C., & Hunter, S. (1998, August 01). Intrauterine Growth Restriction: Identification and Management. Retrieved November 16, 2020, from https://www.aafp.org/afp/1998/0801/p453.html

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