A fundal height measurement is typically done to determine if a baby is small for its gestational age. The measurement is generally defined as the distance in centimeters from the pubic bone to the top of the uterus. The expectation is that after week 24 of pregnancy the fundal height for a normally growing baby will match the number of weeks of pregnancy — plus or minus 2 centimeters. For example, if you're 27 weeks pregnant, your health care provider would expect your fundal height to be about 27 centimeters.

A fundal height measurement might be less accurate, however, if you have a body mass index of 30 or higher (obesity) or have a history of fibroids.

A fundal height that measures smaller or larger than expected — or increases more or less quickly than expected — could indicate:

• Slow fetal growth (intrauterine growth restriction)
• A multiple pregnancy
• A significantly larger than average baby (fetal macrosomia)
• Too little amniotic fluid (oligohydramnios)
• Too much amniotic fluid (polyhydramnios)

Depending on the circumstances, your health care provider might recommend an ultrasound to determine what's causing the unusual measurements or more closely monitor your pregnancy.

But fundal height is only a tool for gauging fetal growth — it's not an exact science. And further research is needed to determine how effective it is in detecting intrauterine growth restriction. Typically, fundal height measurements offer reassurance of a baby's steady growth. If you're concerned about your fundal height measurements, ask your health care provider for details.