What does it mean if a woman measures 29 weeks when she is only 27 weeks pregnant?

"Measuring 29 weeks" implies that the patient measures 29 centimeters, or roughly 9 centimeters above the umbilicus (belly button). Measurements can be off by a few centimeters without any cause for concern--2 cm off would not prompt most physicians to change any treatment plan. The concern becomes if the patient is measuring a large number off; this can mean the baby is either very large or very small (depending if the number is higher or lower than expected), which could prompt the physician to order an ultrasound to give a better estimate of how large the baby is. Where I practice, most insurance companies will not pay for an ultrasound with the diagnosis of LGA (large for gestational age, meaning a much larger measurement than expected) unless the patient is measuring at least three centimeters more than expected.

The measurement also needs to be considered in the context of the whole patient; if the patient's diabetes screen was negative (diabetes can lead to larger babies) and there are no other concerns during the pregnancy, an isolated measurement that is somewhat more than expected doesn't mean as much as it would in a higher risk pregnancy.

Also keep in mind that measuring is somewhat user-dependent; not all physicians measure the same way, so what is 29 weeks to one may be 27 to another.

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Dr. B.

Don't forget of course that 29 weeks pregnant is actually 27 weeks from conception.

The measurement is made from the top of the pubic bone (more or less the bikini line) to the top of the uterus, and is most accurate when done each time by the same person as each person may do it a little differently.

It is the trend which is most important as a big baby will be big all along and a small baby is small all along, a sudden change in size is more important.