July 23, 2009 | No comments | Health
Is ultrasound scan safe in pregnancy?
Ultrasound scans are very frequently used during pregnancy. It is rare to find a mother who has not had an ultrasound scan during pregnancy. Even if the doctor does not recommend an ultrasound scan, most mothers get one done at some point of their pregnancy. But very few are aware of how, when and why it is done.
Whilst most mothers like an ultrasound scan during pregnancy, some mothers panic thinking that it could give rise to side effects etc. Therefore it is worth explaining the mechanism of an ultrasound and what ultrasound is.
The human ear can hear sound waves from 20 – 20,000 Hertz and any sound beyond that range is called ultrasound. Diagnostic ultrasound scan uses 2.5 – 7.5 Megahertz. The ultrasound scan machine is like a computer which can also generate sound waves. These sound waves are generated by the ultrasound probe which emits sound waves through the abdomen when scanning.
Transmission of sound waves differs according to the tissue through which it travels and these sound waves are reflected back to the probe as an echo. A gel is applied on your tummy to aid sound waves to pass in to the tummy, as sound waves would not pass if there is air in between probe and tummy wall. The computer analyses the difference between the sound waves transmitted and reflected and creates an image on the screen.
Are there any side effects of ultrasound scanning?
Ever since the use of ultrasound in obstetrics, a lot of scientists and researchers have done research to look for any side or adverse effects to the fetus. But none of them were able to prove any side effects to the fetus or the mother. Some think that it could give rise to left -handedness, but it has not been proven. Therefore in summary, considering the enormous advantages of ultrasound in obstetrics, one should not panic while having a scan done during pregnancy.
Do pregnant women need ultrasound scans?
Yes indeed. According to scientific evidence, it is advantageous for all women to have an ultrasound scan AFTER 10 WEEKS & BEFORE 14 WEEKS from their last menstrual period. It is best to get it done at 12 weeks and this scan is called a DATING SCAN. In other words, the most important scan during pregnancy is the dating scan. In developed countries this is a routine scan offered universally even without a recommendation of a doctor.
One group of women needs an ultrasound scan as soon as they find that they are pregnant. That is the group of patients who are at risk of having an Ectopic pregnancy (a pregnancy outside the womb, commonly in the tube). Generally it is not common with only about 14 per 1000 pregnancies.
Those who are at risk of getting an ectopic pregnancy are the ones who have had an ectopic pregnancy in the past (the risk increases from 0.14% to 10 – 15 %), pelvic infection, pelvic surgery, those who have had assisted reproductive techniques like sub fertile women who had medication for stimulation of ovaries and in vitro fertilization and those who become pregnant while having an intrauterine contraceptive device (commonly known as a Loop/ Coil) for contraception.
These women need to see their gynaecologist to get a scan done to exclude an ectopic pregnancy.
What are the routes of scanning?
Basically there are two routes. Most scans are done by placing the scan probe on the lower abdomen (Transabdominal). But sometimes, in order to see a clearer picture of an early pregnancy etc, a special probe is used through the vagina (Transvaginal or TV scan) in some patients.
What is a dating scan & how is it done?
Dating scan is a scan done to date the pregnancy so as to give a correct expected date of delivery. Most of the time it is done by performing an ultrasound scan through the abdomen. Usually a gel is applied on your tummy and an ultrasound probe is placed on top of that. Then the correct image of the baby inside the womb is obtained (as shown in the photograph).
By measuring the sitting height of the foetus, (called Crown Rump Length - length from top of the head to buttocks) we can get the correct gestational age of the foetus by using the standard charts. Thereby we can calculate the expected date of delivery.
What is the reason to recommend a dating scan for all pregnant women?
Generally we calculate the Expected Date of Delivery (EDD) using the date of Last Menstrual Period (LMP) given by the mother and adding 280 days (40 weeks) to that. For it to be correct, we assume that every woman is having a 28 day regular menstrual cycle and ovulation (release of an egg) and fertilization takes place on day 14.
But according to evidence, this is incorrect in the case of 10 – 40 % of women .
Even if the menstrual cycles have been regular, some do not remember the LMP exactly. Therefore we recommend this for everybody.
In addition to that, the only reliable way to know the EDD is a dating scan for the following group.
Those with irregular menstrual cycles
Those who become pregnant whilst lactating
Those with regular menstrual cycles but shorter than 21 days or longer than 35 days
Those who become pregnant within 3 months after discontinuing contraceptive pill
Those who become pregnant while using any form of contraceptive method (rare)
Those who have had bleeding after LMP (in early pregnancy) or if LMP is not similar to normal periods
Why should it be done between 10 to 14 weeks?
It is during this period that the variation of the growth of human foetus is minimal. A scan done during this period in any country would have the same measurement for a given period of conception and the difference would be few millimeters, whereas later on, the growth and measurements are dependent on the mother’s and father’s height, race etc. Also we have thousands of data of the measurements of foetus of in-vitro fertilization where the exact date of fertilization is known. According to the above, researchers have found that the most accurate dating is obtained through a scan done during that period.
What are the advantages of having a dating scan?
Firstly to calculate the EDD accurately. It is also said to increase the parental bonding and patient satisfaction. This is the first chance for parents to see their expected new addition to the family moving and its heart beating inside the womb. It also helps to assess the viability of the foetus.
According to medical evidence, another advantage is that it is said to reduce the incidence of unexplained sudden still births. At 37 weeks the incidence of sudden stillbirths is one per 3000 pregnancies and it increases to six per 3000 at 43 weeks. Therefore these women can be induced (A method to trigger labour process artificially by breaking the water bag and starting a hormone drip up) after 41 weeks if the dates are known exactly. As 15 out of 100 pregnant women do not go in to labour naturally at the end of 42 weeks, induction is an important procedure in obstetrics. (NB-Although we give an expected DATE of delivery, it is rather an expected PERIOD of delivery after 37 weeks and before 42 weeks).A dating scan also reduces the incidence of post term pregnancies (pregnancies going beyond 42 weeks).
Furthermore, a dating scan reduces all the unnecessary inductions before 41 weeks. According to scientific evidence, if induction is done before 41 weeks, the chances of failure are high ending up in unnecessary Caesarean delivery. Therefore a dating scan can prevent unnecessary Caesarean sections and its complications. Also since one can wait up to 41 weeks anticipating natural onset of labour without any risk, it also reduces the unnecessary side effects of induction.
Dating scan reduces the number of unnecessary hospital admissions too, especially when they come in with ‘false labour’. Some pregnant women get contractions and pain like labour pains, but they do not go into labour and this is called ‘false labour’. If the Obstetrician is not sure about the correct EDD he is compelled to keep these patients in the ward until they go into labour or until induction and this becomes a reason for overcrowding in government hospitals.
If your doctor or the midwife suspects poor growth of the baby, the only way to diagnose this is by doing an ultrasound scan. To find out if the baby is small or if the dates are wrong, it is invaluable to have had a dating scan as it helps to exclude wrong dates.
One of the most important advantages of a dating scan is the diagnosis of a twin pregnancy as it can be diagnosed in almost 100% of twins at that stage. But later on it is not as easy as this stage. The most important scan for a twin or a higher order multiple pregnancy is the dating scan as the future risk and management is dependent on the findings of this scan related to the nature of the twins.
There are five types of twins depending on the stage of division in their development. The risks are dependent on the presence of one or two placenta for both, lying in a single and two separate water bags etc. The correct type of twins can be identified in almost 100% at this stage. Considering the above, the most important scan in the pregnancy is the dating scan which has to be done after ten weeks and before fourteen weeks (ideally at twelve weeks).
There are other types of scans done during pregnancy but most have to be recommended by your Obstetrician (the doctor looking after you during your pregnancy).
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