Pregnancy Basics: All About the Size of Your Baby Bump

You've probably heard this if you're pregnant: If it's pointy, you're having a boy; if it's round, you're having a girl. The truth is it doesn't matter. Using the shape of your bump to identify the gender of your unborn baby doesn't have any scientific basis. But there is one thing your baby bump can tell you about your pregnancy.  

Once you start showing, your doctor will measure how big your baby bump is growing. The length from the top of the uterus (fundus) to the pubic bone (symphysis pubis) is called the fundal height, also known as the McDonald's rule. It's a measurement tool used by doctors to help date your pregnancy and assess the growth of the baby inside. 

It's not an exact science, but doctors use it as a preliminary gauge up to now. Studies have shown that fundal height measurement can detect pregnancy issues but ideally when it's the same person who measures the bump every prenatal visit. Third-trimester fundal measurements are less accurate than measurements taken earlier in the pregnancy.  

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How does it work? If you don't have a tape measure, the old-school way is to use fingers to estimate the length of your fundus from your navel. The more modern way, of course, is to use a tape measure.  Here's a snapshot of the results of your measurement to the gestational age.  

According to New York City certified nurse midwife Elizabeth Stein, founder of askyourmidwife.com, the fundal height of a pregnant woman should be within two centimeters of the preggo's gestational age. "For example, at 32 weeks pregnant, the range of normal for fundal height is 30 to 34 centimeters," she told Fit Pregnancy. Some doctors give it an allowance of three centimeters.

Fundal height serve as an estimate, not an accurate gauge, so your doctor will recommend an ultrasound and other tests if needed. Several factors could affect your fundal height measurement. Sometimes a full bladder can tweak the measurement, but here are some other reasons why you measure longer or shorter than expected: 

If it's longer than normal range...
Obesity, weaker abdominal muscles, uterine fibroids, a narrow pelvis, or a multiple pregnancy could affect the measurement. Your baby could also be bigger than average. He may be in a breech position or turned sideways. 

If it's shorter than normal range...
A petite built, good abdominal muscles, or if the baby has "dropped" and is ready to come out could also throw the measurement off. 

In either situation, you and the baby can easily be healthy and fine. 

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But if your fundal height measurement increases more or less quickly than average, Dr. Yvonne Butler Tobah of the Mayo Clinic writes that it could indicate slow fetal growth, too little or too much amniotic fluid, or placenta problems. It could also be an early sign of gestational diabetes or pre-eclampsia. It could be a molar pregnancy, but then again, maybe you just need to tweak and improve your diet.

But don't worry too much, though. Any possible reasons for way-off fundal height measurements can easily be pinpointed or resolved by getting an ultrasound. It's the more accurate tool doctors use to monitor your baby's health in your womb. 

Additional sources: ACOG, BabyCenter

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