What does my pregnancy ultrasound report imply?

Q: My child weighs approximately 4 lbs 6oz. I am 36 weeks and 5 days pregnant and my placenta is already a grade 3. What could cause this?

A:We increasingly get queries based on ultrasound reports of a pregnant woman. I want you to understand that a stand alone ultrasound report tells little about your pregnancy. Your baby being healthy or not depends on a lot of factors put together and your treating physician is the best person to tell you that. Ultrasound came into clinical use in pregnancy about 25 years ago and the initial excitement was of looking at the baby (something that could never be done before) but all the benefits claimed have not proven to be true over time. Somehow people have too much faith in ultrasound reports. There are two problems with that. One is that ultrasound is totally observer dependant. Meaning thereby that 3 people doing an ultrasound on the same woman may give three different reports and you cannot base anything on an ultrasound report alone. The second problem is that there is a very wide variation in normal fetuses of weight, size, shape and placental grades. One fetus may be 41/2 pounds and completely normal and the other may be 5 or 6 pounds and still be small for dates. It depends on what the fetus was destined to be under optimal intrauterine conditions. Similarly about the placental grade. In other words Grade I placenta at 36 weeks may be normal and so would grade III. Please understand Placental grade is a sign of prognosis of the fetal outcome but the interpretation is extremely subjective. So please understand that an observer error is possible. And if it is indeed grade III it should not be a problem unless there are other signs of fetal compromise like a significant decrease in the amniotic fluid. Similarly fetal weight estimation at best is approximate. We measure three or four parts of the fetal body like the head abdomen and femur (thigh bone) and make a computer assessment of the volume of the fetus. Then we assume all fetuses in the world have the same specific gravity and calculate the weight. In the best of hands the weight estimations are wrong in up to 30% cases by up to one pound or more. The weight estimates are most wrong when you most need it which is in very low birth weight and very large birth weight. Well on the whole what I am trying to say is that from what you have written the weight and placental grades at this stage are quite OK but ultrasound reveals little in terms of fetal health. Moreover fetal weight depends on your height weight and that of your husband. You are not very tall and we know that petite women have petite babies. Your baby is bound to be smaller that one born to a couple who are 6 feet tall. Well actually in nature if you are small and your baby is large normal labour would be impossible so nature adjusts everything. And just like you may be petite but normal so would your child be, small and normal. From what you have written, assuming that the weight estimate and placental grading in the reports is correct, I do not think you have to worry too much at all. The fetus seems to quite normal though the final assessment is purely clinical depending upon you health (Blood pressure, blood sugars and Hb levels etc and presence or absence of maternal disease) and the decision should be taken accordingly. And the best person to do that is your treating physician.