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Ultrasound scan during Pregnancy

by Dr. Vijith Vidyabhushana, Consultant Obstetrician and Gynaecologist, Colombo South Hospital.

Ultrasound scans are very frequently used during the 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 is it 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 to explain the mechanism of the Ultrasound and what it is. Human ear can hear sound waves from 20-20,000 hertz.

Any sound beyond that range is called Ultrasound. Diagnostic Ultrasound scan uses Megahertz 2.5-7.5. The Ultrasound scan machine which is like a computer which can 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 differ according to the tissue through which it travels and these sound waves are reflected back to the probe as an echo. The computer analyses the difference between the sound waves transmitted and reflected and creates an image on the screen.

Ever since the use of Ultrasound in obstetrics, lot of scientists and researchers have done research to look for any side effect or adverse effects to the fetus. But none of them were able to prove any side effects to the fetus or 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 having a scan during pregnancy.

Ectopic pregnancy

Yes in deed, according to scientific evidence it is advantageous for all women to have an Ultrasound scan after 10 weeks and before 14 weeks from their last menstrual period. It is best to have it at 12 weeks and this scan is called a DATING SCAN.

In other words the most important scan in the pregnancy is the dating scan. In developed countries this is a routine scan offered university 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 (about 14 per 1000 pregnancies).

Those who are at risk of getting an atopic 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 subfertile women who had medication for stimulation of ovaries and in vitro fertilization, those who fall 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.

Routes of scanning

Basically there are two routes. Most scans are done by placing the scan probe on the lower abdomen (transabdominal). But sometimes to see a clearer picturer of an early pregnancy etc a special probe is used through the vagina (Transvaginal or TV scan) in some patients.

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). 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 took place on day 14.

But according to the evidence this is not correct for about 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.

1. Those with irregular menstrual cycles.

2. Those who fall pregnant whilst lactating.

3. Regular menstrual cycles but shorter than 21 days or longer than 35 days.

4. Those who fall pregnant within 3 months after discontinuing contraceptive pill.

5. Those who fall pregnant while using any form of contraceptive method (rare).

6. For those who have had bleeding after LMP (in early pregnancy) or if LMP is not similar to normal periods.

Why should it be done

It is during this period that the variation of the growth of human fetus 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 mother's and father's height, race etc etc.

Also we have thousands of data of the measurements of fetuses of in-vitro fertilization where the exact date of fertilization is known. According to above, the researchers have found that the most accurate dating is a scan done during that period.

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 see their expecting new addition to the family moving, heart beating inside the womb. It also helps to assess the viability of the fetus.

According to the 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 1 per 3000 pregnancies and it increases to 6 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 themselves 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).

Contractions

Another advantage is that it reduces all the unnecessary inductions before 41 weeks. According to the scientific evidence, if induction is done before 41 weeks, the chances of failure is high ending up in unnecessary Caesarean delivery.

Thereby it can prevent the unnecessary of Caesarean sections and its complications. Also since one can wait upto 41 weeks anticipating natural onset of labour without any risk, it also reduces the unnecessary side effects of induction.

Also it reduces the number of unnecessary hospital admissions especially when they come in 'false labour' (some pregnant women get contractions and pain like labour, but they do not go into labour and it 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 it is a reason for overcrowding in government hospitals.

If your doctor or the midwife suspect poor growth of the baby the only way to diagnose is by doing an Ultrasound scan. To find 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 best advantages of a dating scans 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 about 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 two or one placenta for both, lying in a single or two separate water bags etc.

The correct type of twin can be identified in almost 100% at this stage. Considering above, the most important scan in the pregnancy is the dating scan which has to be done after 10 week and before 14 weeks. (Ideally at 12 weeks).

There are other types of scans during pregnancy, but most have to be recommended by your Obstetrician (doctor looking you after during your pregnancy) Pramishka Perera.

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Face masks may help prevent some exposures

by Cheryl Pellerin

Washington - Interim guidance on whether face masks or respirators should be used for personal protection in public places during an influenza pandemic was issued by the U.S. Centres for Disease Control and Prevention (CDC) May 3.

If used correctly, face masks and respirators may help prevent some exposures, but they should be used along with other preventive measures, such as social distancing and hand hygiene, the CDC said.

The agency qualified its guidance by noting information is limited on use of face masks and respirators to control pandemic influenza in community settings, and ‘it is difficult to assess their potential effectiveness in controlling influenza in these settings.’

A flu pandemic is a global outbreak caused by a new flu virus that spreads around the world and puts everyone at risk. Such a virus spreads easily from person to person, mostly by close contact (less than two meters) with infected people who are coughing and sneezing.

A combination of protective actions would be needed during a pandemic, according to the guidance, including washing hands, minimizing exposure by keeping infected people away from others and treating them with anti-viral drugs, having those who care for ill family members voluntarily stay home and encouraging everyone to avoid crowded places and large gatherings.

We know that many times people will want to wear a mask if they think they’re going to be exposed to an infectious disease, and we certainly saw that in [severe acute respiratory syndrome] SARS, said CDC Director Dr. Julie Gerberding during a May 3 teleconference.

SARS is a human respiratory viral disease that was responsible for a major epidemic between November 2002 and July 2003, with more than 8,000 known cases and 774 deaths, according to the World Health Organization.

We wish we had better science to help people prepare for that, Gerberding added, and we are doing the kinds of research studies that are going to give us a lot better information, but those results aren’t going to be available for quite a few months and possibly even a couple of years in some cases, but we didn’t want to wait.

Pandemic influenza remains a very real threat, Health and Human Services Secretary Michael Leavitt said in a statement.

Continue to look for ways to protect people and reduce the spread of disease. The guidance issued today is a good step forward in the broader, multifaceted federal effort to prepare the nation for an influenza pandemic.

The interim recommendations are based on the best judgment of public health experts who relied in part on information about the protective value of masks in healthcare facilities.

Respirators

Face masks are loose-fitting disposable masks that cover the nose and mouth. They include products labelled as surgical, dental, medical procedure, isolation and laser masks.

Face masks stop the wearer from spreading droplets and keep splashes or sprays from reaching the wearer’s mouth and nose. They are not designed to protect against breathing in very small particles. Face masks should be used only once.

A respirator an N95 or higher filtering facepiece respirator approved by the U.S. National Institute for Occupational Safety and Health, is designed to protect people from breathing in very small particles that might contain viruses.

‘N95’ means the filter on the respirator screens out 95 percent of particles 0.3 microns and larger that otherwise could pass through into the respiratory system. Higher numbers mean a higher percentage of particles are screened. N95 respirators, which are disposable and cannot be cleaned, should be worn only once.

N95 respirators usually are used in construction and other jobs that involve dust and small particles. Health care workers like nurses and doctors also use respirators when taking care of patients who have diseases that can spread through the air.

The filter and tightness of fit together determine a respirator’s effectiveness. To be most effective, such respirators must fit tightly to the face so air is breathed through the filter material. Respirators are not designed to fit tightly on children or people with facial hair.

Because it screens out very small particles, a respirator gives a higher level of protection than a face mask.

CDC guidance

The CDC offered specific advice to reduce the risk of infection during a pandemic. Individuals should:

* Avoid close contact and crowded conditions whenever possible, rather than relying on the use of masks or respirators;

* In crowded settings, consider using face masks to protect noses and mouths from other people’s coughs and reduce the likelihood of coughing on others; and

* Use respirators when contact with an infectious person cannot be avoided, such as when caring for a sick person at home.

According to the guidance, people should consider wearing a face mask during an influenza pandemic if they are sick with the flu and think they might have close contact with other people, live with someone who has flu symptoms or will spend time in a crowded public place.

People should consider wearing a respirator during an influenza pandemic if they are well and expect to be in close contact with people who are sick with pandemic flu.

USINFO