Measuring large for due date

A lot of us on the July Expecting Club board are "measuring big," meaning fundal height is two or more inches greater than our number of weeks pregnant. Does measuring big mean we might deliver early or be more at risk for a cesarean?


Peg Plumbo CNM

Peg Plumbo has been a certified nurse-midwife (CNM) since 1976. She has assisted at over 1,000 births and currently teaches in the... Read more

Hello to the July Expecting Club board!

Measuring "large for dates" can be very normal, especially in the third trimester, when individual variations in mothers and babies tend to be more pronounced.

Your own accurate LMP (first day of last normal period) is the best indicator of your due date. Add or subtract the number of days that your cycle is longer or shorter than 28 days to or from your due date.

Actually, the later in pregnancy, the more inaccurate are fundal heights at predicting due dates. If a woman has an internal exam in the first trimester and the uterus is appropriate for her gestational/menstrual age, that is the best predictor of an accurate due date. Remember that a normal pregnant women, even with very accurate dates, can still deliver two weeks early or two weeks late.

Most babies who have not suffered an insult during the pregnancy are roughly the same size until about 32-weeks when the babies who are destined to be bigger start to show themselves. Obviously, mothers who will have ten pound babies grow bigger than those who will have six pound babies.

Large babies can be the result of maternal weight gain, genetics or gestational diabetes. We screen all mothers for gestational diabetes to make sure that we identify those women who may be at risk for having especially large babies. You've undoubtedly already been tested for this.

Multiparity (pregnancy after one or more previous pregnancies) is the most common reason for being large for dates. The uterine muscle and the abdominal muscles are a bit more relaxed so mothers show earlier and the uterus tends to start out a bit larger. Women who have had previous cesarean births may also start out a bit larger.

If a woman is measuring three or more centimeters ahead of her dates, I usually examine all the parameters for dating (LMP, conception, contraception used, positive pregnancy test, size at first visit, quickening, growth pattern, previous growth patterns, ultrasound results). If all the data still points to the original due date, one must consider that this is normal for this particular mother. It does not necessarily mean that she will deliver earlier.

One may or may not consider requesting another ultrasound if the provider is concerned. This could give a guess as to the estimated fetal weight and the amount of amniotic fluid. Rarely, an excess of fluid known as "hydramnios" or "polyhydramnios" is diagnosed and efforts must be directed at discovering why this condition exists.

All mothers and babies are different. A one to three centimeter discrepancy is a very normal finding and should not be a concern for any of you.

I wish you all the best and hope you can escape the summer heat. Be sure to rest more and get plenty of fluids!

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