Tests during pregnancy

Why does one need prenatal tests?

The woman's body undergoes considerable physiological changes during pregnancy that need to be monitored carefully to ensure good maternal and child health. A pregnant woman needs regular medical advice to ensure that the pregnancy runs smoothly and any problem is detected and treated as early as possible.

What are the signs of pregnancy?

The first sign that most women notice is the delay in the date of their monthly periods. There may be other symptoms like nausea and vomiting. Some other signs that may indicate conception are:

• Frequent urination
• Tenderness and swelling in the breasts
• Cravings for certain food items like sweets
• Feeling of exhaustion or tiredness
• Backache

What are the various pregnancy detection tests?

1. Home pregnancy tests – these tests are available as kits. Though they can be used to detect pregnancy fairly accurately, they should always be followed by a check up with the doctor. Home pregnancy tests work by detecting raised levels of the hormone hCG (human chorionic gonadotropin) in the urine. In a pregnant woman, the concentration of this hormone increases in the body and is released in the urine.
   
   To use a home pregnancy test, one must collect urine in a container and dip the test strip into it. Some tests are available in a solution form and the urine drops have to be added to it. After waiting for some time (depending on the kind of test used), the results can be read according to the instructions given. Presently, only one test called 'Pregcolour' is available at chemist shops in India.
   
   
2. Blood tests – a suspected pregnancy can be confirmed with the help of a blood test, which also measures the amount of hCG in the blood and confirms the pregnancy. A blood test is more reliable than a urine test, so both are routinely done to confirm conception.

What prenatal tests should be done?

The various tests that are routinely done during pregnancy include:

• Blood group
• Blood tests for AIDS, hepatitis, rubella, VDRL
• Ultrasound/sonography
• Urine test for albumin
• Other tests may be required in special circumstances, particularly in high-risk pregnancies. These include:
• Alpha-feto protein (AFP)
• Chorionic villus sampling (CVS)
• Non-stress tests
• Amniocentesis

Blood tests – blood tests to diagnose Rh-ve incompatibility, hepatitis, haemoglobin level and platelet count are done as a routine during pregnancy. An ELISA is nowadays also done to check for HIV infection. The specific blood tests are – blood group (ABO & Rh), Hb A2 (to detect thalassaemia carriers), HBs Ag (to check for hepatitis B carriers) and VDRL (for syphilis).

Ultrasound - Ultrasound is a technique that uses sound waves to study the internal parts of the body. High-frequency sound waves (20,000Hz and above), which are beyond the range of normal hearing are transmitted to the area that needs to be studied and the returning echos are recorded. The technical term for ultrasound testing and recording is sonography. It is used to listen to and monitor the fetal heartbeat and to check for any abnormalities in fetal development.

Conditions like Down's syndrome cannot be diagnosed by an ultrasound, but certain abnormalities can be detected which may raise suspicion of Down's syndrome. Abnormalities of the heart, digestive tract and kidneys can usually be detected in an ultrasound scan. Other conditions like spina bifida (spine anomaly) and placental abnormalities can also be detected.

Alpha-feto protein (AFP) – AFP is a test to determine the amount of a fetal protein in the mother's blood and the amniotic fluid. The amount of this protein helps to determine whether the fetus has any abnormalities. It is generally performed between the 15th to 18th weeks of pregnancy. Very high levels of AFP indicate an anomaly of the spinal cord. Low levels of AFP may indicate disorders like Down's syndrome. However, the test is not totally reliable and has to be followed up by an ultrasound or amniocentesis.

Chorionic villus sampling (CVS) – This is a procedure in which a sample of the chorion (the membrane surrounding the baby) is taken for testing. The needle is inserted into the placenta but the amniotic sac is not disturbed. The test is used for checking for any genetic abnormality in the fetus. It is sometimes preferred to amniocentesis since it can be done earlier and the results are obtained sooner. CVS can be done as early as the 10th or 11th week and thus if any abnormality is detected, necessary steps can be taken almost 4-5 weeks sooner than with other procedures. The only disadvantage of CVS is that the rate of miscarriage is almost three times that of amniocentesis.

Amniocentesis – is a test to check for any genetic abnormalities in the fetus and is usually done between the 15th and 17th weeks of gestation. A small amount of fluid from the amniotic sac is taken for testing. Since the needle is brought very close to the baby, this is done with utmost care. The baby's position is marked very carefully before inserting the needle. An ultrasound is done before the procedure to monitor the fetal heart rate, placental position and the amniotic fluid location.

Amniocentesis is advised for some women in the high-risk category. This includes women over the age of 35 years, women who have three or more miscarriages and women who have a family history of chromosomal abnormalities.

Non-stress tests – these are tests done to ensure the good health of the fetus without any invasive technique. The movement of the fetus in response to a sound or tactile stimulation is noted. There may be an increase in the heart rate or a sudden movement by the baby in response to the stimulus. The mother's abdomen is stroked gently and the response of the fetus is noted. If there is no response on repeated stimulation, then a stress test (invasive) may have to be done.