Ultrasounds

FAQ

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This is a compilation of inquiries asked concerning ultrasounds.

Question:
I have been diagnosed with polyhydramnios. I am now 30 weeks pregnant. I went to see a specialist for a more advanced sonogram and was told the only problem I have is the polyhydramnios. I was given a tri-screen at 18 weeks gestation and the results of this were also negative. However I can't help but worry that there is something wrong.

My worry is that a there may still be an undetected birth defect that hasn’t shown on a sonogram or that the ultrasound technician may be keeping something from me. The doctor is reluctant to carry out an amniocentesis. It feels as though they want to give me as little information as possible and part of me is wondering why if everything is okay

Answer:
Most, if not all recognizable causes of polyhydramnios should be clearly diagnosable through ultrasounds examination at 33 weeks. A high percentage of pregnancies with polyhydramnios do not have any visible birth defects in the fetus.

It is true that an amniocentesis may be useful for planning necessary treatment; however your doctor probably felt that the chance of finding a problem with the amnio is too small to warrant the risk. You should actually consider this as good news. I certainly do not believe that your doctor is attempting to hide things from you.

baby faq

Question:
After my scan, my doctor told me that my baby's head is 'smaller than dates', but the limb bone and the abdomen were about right for my estimated due date. Does this mean that the baby has an abnormal head structure?

Answer:
If this is your first ultrasound, then there may be an issue with dates. If a previous scan has validated your due date, then perhaps your baby may have a slightly smaller head. But this may not necessarily mean there is a problem. All of us have different sized heads. You should also be aware that your doctor measures the side-to-side 'diameter' of the fetal head and if your baby has a relatively 'flatter' head, then it will seem 'smaller' on measurement.

This may just be a reflection of your baby’s position rather than anything that you should be alarmed about.
There would need to be a size discrepancy of up to 3-4 weeks before medical ultrasounds professionals would begin to consider abnormalities such as microcephaly ( small head syndrome ).

Question:
I was given a 3d ultrasound at 8 weeks pregnant and the doctor said the fetus is only 7 weeks. He said it was due to my irregular menstrual cycles. I had a further scan at 34 weeks and the doctor said the fetus size was only 31 weeks. In order to fix my due date, should I stick to the results of the earlier scan? If my baby is smaller, wouldn’t it be wise to leave it in the womb for as long as possible so that it can increase in size and be more mature?

Answer:
The result of a scan performed early in pregnancy should always be used for 'dating' purposes as it provides a more accurate estimation. Later on in pregnancy the measurements are affected by growth variations and can no longer correctly reflect the fetal 'age'.

The findings in your particular case apparently indicate that your baby is smaller than average. It isn’t the case that babies who are not growing well should be left inside the womb for longer. In fact the opposite is true. The baby may actually be better cared for outside than in and for this reason these babies sometimes have to be delivered well in advance of the actual due date.

Additional Ultrasounds FAQ

Question:
I had ultrasounds done at 34 weeks. The doctor estimated the weight of the fetus to be 2.0 Kg. I’m worried that this is too small. What is the average weight of a baby at 34 weeks gestation?

Answer:
An average size fetus at 34 weeks weighs about 2.2 Kg. Your baby’s weight of 2.0 Kg is on the 25th percentile line. A baby is considered small-for-dates when it's weight is lower than the 10th percentile line, at 34 weeks this is 1.8 Kg. For further reassurance, take a look at the Intrauterine weight chart.

Your baby is a little on the small side, but it’s not too small. It will also reassure you to learn that estimating the weight of the fetus using ultrasound measurements can sometimes incur errors of over 10 percent. An assessment will normally be made by your doctor along with other ultrasound findings.

Question:
I have an ultrasound scan tomorrow. I wondered how likely it is that I will be able to see the sex of my baby on the screen? I really don’t want to know the sex before my baby is born.

Answer:
The chances of you recognizing the genital organs of your baby without any help are very slim. Interpreting ultrasound images requires a great deal of training and skill; it is not like looking at a photograph of someone taken in front of you. Usually patients are unable to actually 'see' parts of the fetus that the doctor carefully studies during a scanning session.

Question:
When my friend was about 7 weeks pregnant, she went to ER because she was in a great deal of pain. She was given ultrasounds scans and when no sac was found in the uterus she was asked to go home. She was then admitted again two days later to another hospital with massive bleeding from an ectopic pregnancy. Why was this missed initially on the first scan?

Answer:
Ectopic pregnancy is notoriously difficult to diagnose early, as the physician always has to exclude three other conditions in early pregnancy which cause pain.

1. Pain can be present for no apparent reason in early pregnancy, most likely due to uterine and venous engorgement.

2. Pain can be caused as a result of missed or inevitable abortion.

3. A ruptured ovary lump or pain originating from other abdominal organs.

Unfortunately, ultrasound is not capable of making a 'definitive' diagnosis of ectopic pregnancy. In the majority of cases it is not possible to visualize the actual gestational sac in the fallopian tubes. The fact that a gestational sac can’t be seen in the uterine cavity may just mean that the pregnancy has not been developing normally, or that some sort of an abortion may have occurred. It is also possible that due to an irregular menstrual cycle, is not as advanced as originally thought.

Menstrual history often needs to be considered by the doctor, along with the date of the positive pregnancy test, the intensity of the pain, physical signs, a blood count and results of an ultrasounds scan.

Question:
I would like to find out as much as possible about molar pregnancies. I underwent emergency surgery last year because of this condition.

At the time, I was told very little about it. I would specifically like to find out what exactly a molar pregnancy is, what causes it, what the chances are of having one, and how difficult it to follow a molar pregnancy with a normal conception/pregnancy. Any information you can provide about previous studies of this condition is greatly appreciated.

Answer:
Unfortunately I can't provide you with detailed descriptions about specific diseases. I would suggest that you use a search engine to find the information on ultrasounds and pregnancy that you are looking for.

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