Hi,
Calcification is a sign of placental aging. In fact the amount of calcification, seen as white specks on the ultrasound, can tip off a doctor as to how near term a pregnancy is. But it can also be a sign of premature aging, which will decrease the amount of nutrition and oxygen going to the baby. The more calcification, the less placenta is normal tissue for supplying the baby. Don't panic, though.
The placenta has a lot of slack. There can be considerable calcification before there's really any compromise to the baby. Certainly a placenta that's very calcified (Grade 3) during the 2nd trimester, instead of the 3rd trimester, will be a concern. But for the most part, the grading of the placenta (Grades 1, 2, and 3) is a fuzzy parameter at best. It can be useful, though, in warning of the bad effects of smoking and hypertension on a placenta, and with it, on a pregnancy.

It is said that smoking has a direct effect on calcification of placenta. So it is advised to avoid smoking. Also, there are some dietery recomendations for decreasing premature calcification in placenta. For more information read here...

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regards
Dr. Gupta