Pregnancy Test

OutLine

• Introduction.
• Types of tests.
• Basis for the test.
• Home pregnancy tests.
• Laboratory confirmatory tests.
• False Positives & Negatives.
• Other prenatal tests.
• Viability tests.

 

Introduction:

The earliest pregnancy test was based on early pregnancy factor. This test can be performed within 48 hrs of fertilization but very costly. But at present there are lot of ways to detect pregnancy at an early stage. Tests are available to confirm pregnancy at home itself.

 

Types of tests:

Some of the confirmatory tests available now are;

• Home pregnancy tests.
• Quantitative serum analysis.
• Urine analysis
• Qualitative analysis.
• Sonograms.
• Physical examinations.

 

Basis for tests:

Most chemical tests for pregnancy are based on the presence of beta subunit of HCG or human chorionic gonadotrophin in the blood or urine.HCG can be detected in urine or blood after implantation, which occurs 6-12 days after fertilization.

Trophoblast cells of the embryo which gets implanted in the uterine endometerium secretes this hormone which is later continued by placenta.

Quantitative blood analysis requires a minimum level of 1mIU/ml, of HCG to detect pregnancy when compared to urine test, qualitative test which requires a level of 20mIU/ml n and a level of 25 mIU/ml respectively. Thus the Quantitative blood analysis serves the best and is highly sensitive.

 

Home pregnancy test:

Home pregnancy tests have become common nowadays. Though they are very much helpful and fairly accurate, their results always should be confirmed with a doctor.

• In pregnancy, the growing tissues of the new conception (early foetus) secrete a special hormone into your body called ‘Human Chorionic Gonadotrophin’ (HCG). This enters your blood as early as 10-12days following fertilisation. This can be traced from blood or urine by special tests. Home tests are done with urine.
• Depending upon the type and sensitivity of the test used, pregnancy can be detected as early as a day or two from the missed period.
• Technique for the usage of these tests will be included in the pack itself.

Usage:

These kits are user friendly. First

·         Urine should be collected in clean detergent free bottle.

              Preferably first morning sample is used as it contains more of HCG hormone levels.

·         Urine is then taken in the dropper given with the kid.

·         Only 2/3 drops of urine are added to the well where it is indicated.

·         If there appears a pink line in the place indicated as tests and other pink in the control region then the tests is positive.(2 pink lines).If only one line appears in the test region then the test is negative, and if no lines appear then the test is invalid.

·         Method of testing differs according to the brand.

It may happen that a test result comes negative although, in reality pregnant. This is more likely if:

• The cycles are irregular or are often delayed.
• The testing has been done very early in pregnancy. In such cases, if the test is repeated after one week, it may become positive. It is always advisable to confirm the pregnancy diagnosis by a qualified medical practitioner as all tests have their limitations.

 

Laboratory confirmatory tests:

• Serum beta Hcg/quantitative blood tests

             This is the most sensitive test for pregnancy and detects the hormone even at earlier levels.

• Urine tests

              This test is also based on the increased levels of HCG but less sensitive when compared to blood tests.

• Sonography-ultrasound scan can also be used for diagnosing pregnancy. Gestational sac can be visualized as early as four and half weeks of gestation (2˝ weeks after ovulation).It is not necessary if the periods are regular and LMP (last menstrual period) is known. It is necessary if:

Bleeding after missing a period.

To ensure if the growth is proper.

To rule out ectopic pregnancy.

 

False positives and negatives:

False positives:

          In home pregnancy tests, there appear evaporation lines if the test is read after the specified reaction time independent of actual pregnancy.

          Women treated with HCG injection as part of infertility treatment, test positive irrespective of actual pregnancy.

           Some diseases like choriocarcinomas, IgA deficiencies, heterophilic antibodies, and even lung cancer also show elevated levels of HCG, giving false positive results.

False negatives:

The most common reasons for false negative result is when the testing is done very early.Quantative urine tests and the most sensitive urine tests can detect pregnancy as early as 6-12 days after implantation. but the less sensitive home pregnancy tests require adequately elevated levels of hormone to detect it.Menstrution occurs after 14 days of ovulation and the likelihood of false negatives decreases once a menstrual period is late.

 The accuracy of pregnancy tests is related to the day of ovulation not the day of intercourse.Because it is normal for the sperm to be waiting in the fallopian tube for 5 days. Once the egg is released fusion takes place leading to the formation of zygote. But it will take another 12 days for it to get implanted. Thus after implantation only there will be rise in HCG levels. Thus it takes approximately 17 days after intercourse .Any tests taken before this period will give negative results. Moreover it takes a few more days to reach adequate levels to be detected by less sensitive pregnancy tests.

 

Other prenatal tests:

The various tests that are routinely done during pregnancy include:

•  Blood group detection.

To identify the blood group and Rh factors to prevent complications later.

•  Blood tests for AIDS, hepatitis, rubella, VDRL

Elisa tests is  carried on to rule out any sexually transmitted diseases, specific blood tests to find out HbA2 (Thalassemia carriers ),HBsAg (hepatitis B carriers.).VDRL to diagnose syphilis.

•  Ultrasound/sonography to check for foetal heart beat and any abnormalities in foetal development.other conditions like spina-bifida and placental abnormalities can also be identified at an earlier stage.

·          Urine test for albumin.

Other tests may be required in special circumstances, particularly in high risk pregnancies. These include :       

• Alpha-foetal protein (AFP) takes the measure of particular fetoprotein levels in the foetus and the mother’s blood to rule out any developmental abnormalities of the foetus.
• Chorionic villus sampling (CVS) takes the measure of chorion covering the baby to detect any genetic abnormalities in the baby.
• Non-stress tests done to detect the response of the foetus to any external sound and tactile stimuli.
•  Amniocentesis done with the fluid carefully taken from the amnion of the baby tested for any genetic abnormalities.

 

Viability tests:

             Many pregnancy tests are used to study the viability of the pregnancy, series of quantative blood tests are taken to measure the gradual changes in the blood levels of HCG against a normal standard levels. Any abnormalities denote increased chances of miscarriages and ectopic pregnancy.

           Ultrasound can also be used for this purpose. The growth of the foetus is visually seen at regular intervals .Any abnormalities can be easily detected from the scan.