Q: My OB recently started measuring my belly every time I see her. Why does she do this?
A: Starting between the 12th and 14th week, many doctors and midwives perform a fundal height measurement at each prenatal visit to monitor the fetus’s growth. This involves measuring the distance from the top of the pelvic bone (symphysis pubis) to the top of the uterus (fundus).
In addition to looking for continued and appropriate growth from visit to visit, your doctor or midwife is watching for specific growth markers. “Measurements between 20 and 36 weeks should be within 2 centimeters of the weeks of gestation,” explains Elizabeth Stein, C.N.M., M.S.N., M.P.H., a midwife in New York City and the founder of askyourmidwife.com. “For example, at 32 weeks gestation, the range of normal for fundal height is 30 to 34 centimeters. Any measurement larger or smaller should be a red flag that needs further evaluation.”
If your doctor or midwife does see a red flag, she will likely recommend a biophysical profile, which typically includes an ultrasound to evaluate the fetus’s growth and weight and your amniotic fluid level. “In addition, the woman’s nutrition should be reviewed to make sure she is eating properly, and she may need additional testing for gestational diabetes,” Stein says.
So how accurate is fundal height measurement at detecting potential problems?
Studies show detection rates range anywhere from 17 percent to 93 percent, with an average of 65 percent (but with a 50 percent false-positive rate). In other words, Stein says, “It’s subjective at best and most accurate when done by the same person at every visit.” She points out that a woman’s height, weight gain and body fat should also be taken into account.