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Pregnancy testing: a positive result is just the beginning

Julie Smith
SRN ONC
Specialist Nurse
General Practice Nursing
Chaddlewood Surgery
Devon

It is clear to every health professional that over the past ten years the way in which we work has changed, and this directly affects our provision of care to clients. Our practice has changed in that it is not historical codes of care that we use but evidence-based ones, meaning there is reliable evidence of clinical effectiveness. We have also recognised the importance of informed consent, which involves the client being empowered with knowledge to enable decision-making in healthcare. This can be clearly illustrated in the skill of pregnancy testing.

Home pregnancy testing kits
We see advertisements everywhere for pregnancy tests. Each test claims to be easy and accurate. Pregnancy testing kits are easily available from pharmacies and elsewhere to allow women to confirm or exclude pregnancy in the privacy of their own home. But how reliable are they?
A review of studies suggests that all is not as simple as it seems.(1)
A thorough search strategy identified 55 studies, of which 45 were immediately excluded because they were reviews or because the kit examined was not compared with a reliable laboratory standard. Of the remaining ten, five more were excluded because studies had no control groups of nonpregnant clients, sensitivity and specificity could not be calculated from data given, because the kit demonstrated poor performance or was not available, or because the study was small. In the latter category was the remarkable report which tested kits on just three people!
The results were that five reasonable studies showed that when the subjects using the tests were volunteers who previously collected samples, the overall sensitivity was 91% (range 52%). Specificity ranged from 61% to 100%. The female subjects collecting and testing their own samples had an overall sensitivity of 75% (range 53-82%). Specificity was also low, ranging from 52% to 75%.
Home pregnancy testing kits usually claim accuracy of over 95%. In reality the literature contains information on only four kits evaluated as they are intended to be used - that is, by women testing their own urine.
The results quoted suggest that for every four women who use such a test and are pregnant, one will get a negative result. It also suggests that for every four women who are not pregnant, one will have a positive test result.
Many important decisions will be made by a woman empowered to make her own choices with a home test result, such as whether to see a doctor, decisions about termination and decisions about relationships. In the circumstances, the paucity and quality of published information could be regarded as a scandal. While results in experienced users may be adequate, it is clear that in the situation in which they are intended to be used, there is not enough information. Women should know this.

Types of pregnancy tests
What types of pregnancy tests are available and, more importantly, give accurate early results?
There are two basic types of pregnancy tests, blood and urine. They are both used to test for the presence of human chorionic gonadotropin (hCG). This is a hormone released by the placenta immediately after the embryo begins implanting into the uterine lining.
Blood tests are the more accurate of the two types of test but not necessarily the more sensitive. A lot depends on the lab quantitative blood test, usually called a beta hCG test, measuring the exact units of hCG in the blood. That means it will detect even the most minimal level. 
There is another type of blood test sometimes called a qualitative hCG. This is a test that simply gives a yes or no answer to whether you are pregnant. Just like urine tests, laboratories vary as to what is considered a positive pregnancy test. Common cut-offs for positive are 5, 10 and 25 units. A level under 5 is considered negative. A test that is only triggered at 25 units of hCG is not any more sensitive than several of the urine home pregnancy tests. 
Urine tests are accurate in detecting the presence of hCG. However, the amounts detectable by home pregnancy tests and laboratories vary. The level of units in these is not uniform. Manufacturers claim that sensitivity ranges from 20mIU to100mIU (20mIU being the most sensitive and giving the earliest results).
Wilcox et al. found the highest possible screening sensitivity for a hCG-based pregnancy test conducted on the first day of a missed period to be 90%, as 10% of women may not have implanted yet.(2) The authors estimate that the highest possible screening sensitivity of a home pregnancy test by one week after the first day of the missed period is 97%.
Pregnancy can also be detected by ultrasound and, even in undisclosed types, by simple palpation.
The earliest that a positive result can be gained on the most sensitive pregnancy test is seven days after ovulation. Implantation needs to occur before hCG is produced, and that usually happens 6 days after ovulation. For this reason it makes economic sense to wait until 10days after ovulation, although even then a significant percentage of women who are pregnant will get a negative result. If you have not had a hCG injection - common in fertility treatment - the test may be positive, but beware of a false-negative. 
If the period is late, test again. The hCG levels should double every two to three days, and many women do not have a positive home pregnancy test until the first day of a missed period or even a few days later.
It is extremely important that the patient carries out the test according to the datasheet supplied with the individual kit. It is essential that we advise patients to read through the instructions carefully before doing the test!

Helping the patient deal with the result
The impact of a positive pregnancy test cannot be stressed enough. However, the clinician needs to remember that it is not their pregnancy - it is the woman in front of them. Depending on how she wants to use the knowledge that she is pregnant, the clinician can help with the choice.
If the pregnancy is unplanned then a woman needs to be able to talk with someone she trusts and learn about the options. This may involve parenting, adoption or abortion.

Parenting
This involves a lifelong investment of emotional, physical and financial resources.
Young parents often have more stress and difficulty than adult parents because they have fewer resources. Many teenagers are happy with their decision to have children, but say that raising a child is more difficult than they ever imagined.

Adoption
Adoption involves continuing with a pregnancy and having a child, and then placing the child with another family to raise. This can be a good choice for young women who do not want to have an abortion.

Abortion
Abortion is a medical or surgical procedure that ends a pregnancy. There are several methods, and the woman will be offered the appropriate one depending on the length of pregnancy.

Consideration of beliefs and resources
It is important that all options are fully explored as any choice will involve decision-making based on a woman's life, beliefs, goals, plans, strengths and weaknesses. Try to find out if the woman has trusted friends, a partner or family that she can talk things over with. It is a time for a woman to reach out to a support system that can enable her, with the right information and effective advice, to be empowered to come to her own choice.

References

  1. Bastian LA, Nanda K, Hasselblad V, Simel DL. Diagnostic efficiency of home pregnancy kits. A meta-analysis. Arch Fam Med 1998;7:465-9.
  2. Wilcox AJ, Baird DD, Dunson D, McChesney R, Weinberg CR. Natural limits of pregnancy testing in relation to the expected menstrual period. JAMA 2001;286:1759-61.

Resources
Marie Stopes
W:www.mariestopes.org.uk
Family Planning Association
W:www.fpa.org.uk
National Campaign to Prevent Teen Pregnancy
W:www.teenpregnancy.org