Fetus Too Large

Four weeks ago, ultrasound showed my baby at two and a half pounds. I'm now 30 weeks pregnant and the baby is already five pounds. I started out at 190 pounds and have only gained 12 pounds. All of my tests have been normal and my blood pressure is fine. I quite sure of my dates, but all the ultrasound measurements put her at 32 1/2 to 33 1/2 weeks, not 30. Will I have a 12-pound baby?

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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

Second babies are usually larger, but I doubt you will have a 12-pounder, especially without a large pregnancy weight gain.

Ultrasound is notoriously inaccurate at predicting fetal weight. If the earlier one was done before 20 weeks, that is the more accurate in terms of a due date. Other things should be considered such as the growth of the uterus at your clinic visits and the provider's estimation of size and dates. If the care began early (before 10 to 12 weeks), a more accurate estimation of uterine size was done at your first visit. Clues such as possible conception date, LMP, quickening, fetal heart tones can add to the picture.

Sometimes a large-for-gestational-age baby can be caused by maternal blood sugars as would occur in gestational diabetes. I am assuming a test was done about 28 weeks and this was within normal limits. If it was not done, you should have the screening test followed by a three-hour GTT, if this was not normal.

Try not to worry. Sometimes we allow our technology to cloud our clinical reasoning and judgment. I hope all goes well for you and for your family.

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