During your pregnancy, your health-care provider may recommend a variety of tests that are intended to confirm that your baby is developing normally. The decision whether to have these tests or not is yours – you do not have to agree to any procedure you are not comfortable with. Understanding the procedures involved, why the tests have been offered, and what they will tell you about your baby, will enable you to make an informed decision.

SCREENING TESTS

These procedures consist of ultrasound or blood samples to check for abnormalities in the baby and/or disease in the mother. Their attraction for many women is that unlike diagnostic tests they’re noninvasive and therefore pose no threat to the baby. However, screening tests won’t give you a definite “yes” or “no” if, for instance, you want to know if your baby has Down’s syndrome. They can also give “false positives”, indicating there’s a problem with the baby when everything’s in fact fine, or “false negatives”, indicating that everything’s fine with the baby when it isn’t.

ULTRASOUND

This technology makes use of sound waves and their echoes to create a picture of the uterus and developing baby. Ultrasound examinations are painfree, and cause no harm in the short or long term to you or your baby.

Ultrasound scans can be performed either transvaginally, using a probe that inserts into the vagina, or trans-abdominally, using a transducer that is moved across the mother’s abdomen. The technology of scanning is evolving rapidly, and 3D technology is now widely available. 3D means that a life-picture of your baby can be built up from images taken in each of the three planes of vision of the scanner. These images are covered by computer to a full picture. The term 4D refers to a moving 3D image. These scans take no longer than conventional 2D scans because all the pictures are taken simultaneously.

Doppler ultrasound scanning traces the blood flow between placenta and your baby through the umbilical cord. Using colour, the sonographer can more easily identify the different blood vessels. Doppler scanning usually can be done during the anomaly scan to check on any placental problems.

Scans performed before 8 to 10 weeks of pregnancy are usually done vaginally because this gives a clearer picture, being much closer to the baby at this stage of pregnancy. Occasionally, you may need a transvaginal ultrasound later in pregnancy to examine the cervix. Although it’s understandable to worry, there is no evidence that the probe can harm you or your baby.

Scans later in pregnancy are usually done transabdominally since the baby is clearly visible in the abdomen by then. Gel il spread over the abdominal skin and the transducer is moved on the gel. The sound waves travel through liquid such as the amniotic fluid but are reflected (bounced back) by more solid structures ass the heart, brain and uterine wall. The quality of the pictures depends on several variables:

• The quality of the scanning machine;
• The training and skills of the person doing the scan;
• The length of time for which you are scanned;
• The way your baby is lying (sometimes the scanner can’t see the heart clearly so you may be asked to go for a walk to alter the baby’s position before scanning is resumed);
• Whether you are overweight, or there is a lot of scar tissue.

In pregnancy, ultrasound scans are used for several types of reasons depending on the stage. Early in pregnancy, a scan can help confirm the dates and make sure the pregnancy is in the uterus, not the tube (ectopic pregnancy) and that the baby is viable (i.e. you have not miscarried).

Scans can be used to help in diagnosis of a problem, for example, if you have twins, or as a screening procedure to see whether you have a normal or higher risk of an abnormality such as Down’s syndrome or congenital heart disease. Scans also can help show whether the placenta is in the correct place, whether the baby is growing well, and can determine the sex of your baby. Finally, scanning is used to aid other procedures such as amniocentesis and CVS.

Although scanning is a useful aid, it can supply only a certain amount of information and may pick up anomalies that rectify themselves or miss small problems. They must be interpreted along with all the other data available.

As an NHS patient, you will be routinely offered at least two scans during your pregnancy.

EARLY/DATING SCAN

This is usually carried out between 11-14 weeks of pregnancy. All women who book before this stage in pregnancy are counselled and offered the Nuchal Translucency Scan at this appointment as well. The scanhelps for the following reasons:

• Locate the pregnancy – Is it in the uterus?
• Establish an accurate due date – Scans done before 20 weeks give a much clearer indication of the delivery date than later scans.
• Check the number of babies – If you have twins (or more), the appearance of the membrane sperating the babies and the position of the placenta can show whether the babies share one placenta or have one each.
• Check the uterus and ovaries – The size and shapes of the uterus and appearance of the cervix are assessed, and if you have fibroids (common benign overgrowths of the muscle wall of the uterus), thy can be measured. Sometimes a small ovarian cyst is seen, which formed when the egg was released. These corpus luteum cysts disperse during pregnancy. Occasionally larger ovarian cysts are noticed, unrelated to the pregnancy.
• Assess the risk of Down’s syndrome – The nuchal translucency screening test involves measuring a special fluid-filled area behind the baby’s neck. If this is thicker than average, the risk of Down’s syndrome is increased, and you’ll be offered further testing, including blood tests, amniocentesis and CVS. Bear in mind that even if your risk is higher, there is still a good chance that the baby is absolutely normal.

ANOMALY SCAN

This is performed at around 16 to 22 weeks and is much more detailed than the early scan.It is used to check the following:

• Fetal anatomy – This looks at all the baby’s organs including the brain and spinal cord, heart, chest cavity, stomach, face, kidneys and bladder, and arms and legs. Even the number of toes and fingers can be counted, if the scan suggests an abnormality, you may be referred for an MRI (magnetic resonance imaging)  scan to evaluate it further.
• Gestational age
• Growth rate – The lenght fo the baby is measured from the head to the bottom; this is called the crown-rump lenght.
• Amount of amniotic fluid
• Location of the placenta – The position, size and function of the placenta is checked. If the placenta is low-lying, near or across the cervix, you will be rescanned later in pregnancy. If, later on, the placenta or its blood vessels are seen to cover the cervix, you will need to have a Ceasarian. The placenta can be investigated further using colour doppler scanning to trace the blood flow through the umbilical cord.
• The baby’s gender – After 16 weeks it is often easy to see if you have a boy or a girl. Don’t depend completely on this thought!

FURTHER ULTRASOUNDS

A number of ultrasound examinations may be needed if any of the following arise:

• Multiple pregnancy.
  
• Problems with the baby’s growth rate (too small or too large).
  
• Too little or too much amniotic fluid.
  
• High risk for premature labour.
  
• Diabetes, high blood pressure, or other medical problems that may affect the baby’s growth.
  
• If you’re pregnant ad bleeding.
  
• If you have a low-lying placenta.
  
• If you are 41 weeks pregnant or more.

Source: Your pregnancy bible by dr. Anne Deans – Carroll & Brown

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