Some women are smaller than average for a variety of reasons. Find out why this happens.
Q. During my last prenatal visit, my midwife measured my uterus and said that I'm a little small. Now I'm worried that something is wrong. What causes this?
A. If your midwife didn't order another diagnostic test, such as an ultrasound, and if she didn't seem concerned about the baby's heart rate or activity level, there's nothing to worry about. Some women may measure smaller than expected for many reasons: The baby may be small because you are small, the baby may be transverse, or the baby's head may be positioned deep in the vagina.
If your baby doesn't gain adequate weight in the 3rd trimester, however, you may have a condition known as intrauterine growth restriction (IUGR). This describes any baby that consistently measures smaller than he should given the length of the pregnancy. It's most common in situations where the expectant mother suffers from a chronic health condition such as high blood pressure or when there are twins or more. It can also be a sign of abnormalities in the baby or the placenta.
Typically, a practitioner who suspects IUGR will first carefully review the gestational age, which in most cases was based on a sure last menstrual period, early pelvic exam, and/or an ultrasound prior to 20 weeks. Due dates do not get shifted at this late date based on the baby's size unless there was a mistake made early on.
If the due date is accurate and the baby simply isn't growing, the next step is an ultrasound to measure the baby's head, long bones, and abdominal circumference. This will show an estimated fetal weight and where your baby is on the growth curve. The ultrasound also allows the doctor to see if your baby is small but healthy and moving around or if your baby is small and sluggish. If he is healthy, the doctor may tell you to be patient and let your baby grow in his own time. If he is too small or not perky enough, the doctor may order more fetal testing. He may even decide to deliver the baby, especially if you are at 37 weeks or later.
Originally published in You & Your Baby: Pregnancy.
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