When you measure too small or too large

Around 20 weeks your doctor or midwife will likely begin to measure your fundal height. Your fundal height is the measurement in centimeters from the top of your pubic bone to the top of uterus. The measurement will give your provider a good idea of fetal growth. Between 20-36 weeks your measurement should be within 2cm either way. Therefore, at 30 weeks your measurement should be 28-32cm. As you can imagine, there are so many reasons why this measurement could be off.

Some reasons for small fundal measurement:

  • Tall/slim frame of the mother
  • Position of the bladder
  • Placement of the baby
  • Strong abdominal muscles
  • Intrauterine growth restriction (IUGR)
  • Too little amniotic fluid
  • Baby descending into pelvis prematurely

Some reasons for large fundal measurement:

  • Short/Stocky frame of the mother
  • Full bladder
  • Weak abdominal muscles (especially after multiple pregnancies)
  • Macrosomia-excessive fetal growth (many factors could contribute to this)
  • Placement of baby
  • Too much amniotic fluid

Some other reasons for measurements to be off could be that each provider you see could be measuring differently. Many studies have shown that in order to be more accurate the measurement needs to be done by the same provider at each visit and the woman’s height, weight gain and body fat should be taken into account.

Why am I writing about this? Because with my first pregnancy I consistently measured 2cm small and then at week 36 I measured 3cm too small. They scheduled an ultrasound for my 37 week appointment. This meant that I had to wait an entire week to find out why I was measuring small. Being a nervous Nelly and a first time mom I was so nervous and of course was worried about all of the crazy possibilities that could be causing her to be small. When I had the ultrasound they told me that she was small and would not be more than 6lbs at birth, but she was within normal range. I felt better and was shocked to learn that I would be having a small baby. My great grandmother, grandmother and mother all had babies who were 8lbs-11lbs. Well, my daughter was born 5 days early at 7lbs 11oz. Under 6lbs?? Surely, these measurements are not the end all be all. Fast forward to my current pregnancy (I got pregnant with baby #2 the month my daughter turned 1) and I am measuring small earlier. I measured 26cm at 28 weeks and then 27cm at 30 weeks. Naturally, they decided to do an ultrasound to measure his growth and they are measuring him as small and in the 38th percentile of normal range. I do not blame my providers at all for sending me for these tests. I completely understand that they would rather rule out issues, but I kind of have a feeling that he will be similar in size to my daughter. I think my size and frame are really causes these measurements. I also think that because I have tilted uterus he is hidden back farther. We shall see in about 10 weeks!

Reasons for large fundal measurement:

 

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