Pregnancy kits test for the presence of what hormone

Pregnancy Test

Pregnancy testing is often determined by hospital-specific protocols. It can also be based on clinical indications such as sexual activity, birth control use, and date of the last menstrual period. Another important factor that should be considered is the potential for the planned surgical procedure harming a fetus, based on direct injury (e.g., uterine surgery), reduction in blood flow (e.g., major cardiac or vascular surgery), and exposure to teratogenic agents (e.g., x-rays). The 2012 ASA “Practice Advisory for Preanesthesia Evaluation” suggests offering pregnancy testing to female patients of childbearing age when the result would alter the patient’s management. It also recommends that informed consent be obtained for such testing, or that there be a full discussion of the risks, benefits, and alternatives related to preoperative pregnancy testing. The NICE guidelines recommend that all women of childbearing potential be asked whether there is any possibility they could be pregnant, and that any women who could possibly be pregnant be made aware of the risks of anesthesia and surgery to a fetus. The guidelines also recommend documenting all discussions about whether or not to carry out pregnancy testing, and to conduct pregnancy testing with patient consent if there is any doubt about pregnancy status.274

Pregnancy kits

Pregnancy tests are one of the most commonly used POCDs used by patients at homes or in a clinical setting. The current generation of pregnancy tests based on monoclonal antibodies was introduced in the 1990s to provide accurate results in less than 5 min. The majority of the home pregnancy tests are about 99% accurate [24S]. The reasons for inaccurate results in home pregnancy tests can be attributed to difficulty in understanding product instructions and inability to read test results correctly, testing being done before there is sufficient presence of human chorionic gonadotrophin (hCG) in urine, and/or unusually high concentrations of hCGβcf, the core fragment of β-hCG, which can occur in later stages of pregnancy and when the samples are tested on peri- and post-menopausal women [25R].

Pregnancy as a Stress Test

Pregnancy has been described as a physiologic stress test because women with certain pregnancy complications have increased risks for developing chronic disease at a relatively young age following their first affected pregnancy. It has been theorized that early intervention following the first complicated pregnancy may keep these women below the threshold for clinical cardiovascular and metabolic disease both during and after subsequent pregnancies, thus delaying the onset of disease until much later in life (Fig. 26.1).1Pregnancy and the postpartum period may provide a window of opportunity to identify risk factors and offer interventions to improve long-term health among women and their children.

Home pregnancy test accuracy

Home pregnancy tests can be very accurate, with some tests having robust data to show they are >99% accurate in detecting pregnancy from the day the period is due. But, some currently marketed tests have shown lower accuracy in studies. A recent study examining the analytical sensitivity and women's interpretation of eight home pregnancy tests found varying degrees of accuracy between products. The best performing test (Clearblue Digital) returned >99% correct results when tested at the device sensitivity and read by users, in comparison with the worst performing test which only 33% of users correctly interpreted [36]. An important factor in pregnancy test performance is usability.

Pregnancy Test (hCG) Routine, Serum and Qualitative—Urine

Typical Assay Procedure and Performance

Clearblue pregnancy tests can be simply carried out in the home by holding the test stick sampler directly in the urine stream for 5 s. The device is then removed and the cap replaced. After 1–3 min, the result can be read either visually or by opto-electronics incorporated into a digital reader.

All Clearblue pregnancy tests are 99% accurate at detecting pregnancy from the day the period is due. The high sensitivity of the Clearblue pregnancy tests means that many pregnancies can be detected up to 4 days before the period is due. As the rise in hCG can vary between women, not all women who test before their period is due will get a “Pregnant” result.

Pregnancy Tests

Pregnancy tests detect a hormone that is present in the blood and urine of a pregnant woman. This hormone is human chorionic gonadotropin (hCG), which is secreted by the syncytiotrophoblast of the implanting blastocyst and from the placenta soon after pregnancy is established. In the past, bioassays were used to detect the presence of hCG. In these tests, a woman’s urine was administered to test animals such as mice, rabbits, frogs, and toads. Because hCG acts like luteinizing hormone (LH), when present in the urine it causes ovulation in female animals or spermiation in male animals. One disadvantage was that most of these bioassays could not detect the presence of hCG until two to four weeks after the missed menstrual period. Another disadvantage was that many animals were killed. Fortunately, more effective pregnancy tests have been developed.

The current method of detecting pregnancy utilizes the fact that a monoclonal antibody to hCG (anti-hCG) can be obtained. When hCG is present in a solution, anti-hCG combines with it to produce a visible color reaction. In such an immunoassay pregnancy test, anti-hCG and urine are mixed in a test tube or on a glass slide, and the presence or absence of a certain color is noted. This kind of test takes about 2 h. A deficiency of this method is that in some cases a color forms when hCG is not present; this is due to the interaction of anti-hCG with other proteins in the urine and not to hCG. Also, a negative response can be obtained in a newly pregnant woman. This can occur because the test is done before hCG is secreted in high enough levels to be detected. Most urine tests are not sensitive enough to detect hCG until about 15 days after fertilization (about one day after the missed menses). Several home pregnancy test kits are available without prescription; they tend to be less accurate than laboratory results from a clinic or doctor’s office. Therefore, if one of these kits is used, one should be aware of possible inaccuracies.

An extremely accurate pregnancy test uses radioimmunoassay of hCG in a woman’s blood. With this method, hCG can be detected a few days after implantation. However, a more limited number of clinics have the facilities to perform this procedure, and it is more costly than the urine method.

All these pregnancy tests can give inaccurate results, especially if done in the first two weeks of pregnancy. Not only do the immunoassay tests sometimes give false positives and negatives, but some abnormal kinds of embryonic tissue, such as hydatidiform moles, as discussed later, can secrete large amounts of hCG when no embryo is present. Also, a woman with an ectopic pregnancy (in which the blastocyst implants outside the uterus) may not have detectable levels of hCG in her blood. Failure to detect an ectopic pregnancy can be dangerous. Thus, a woman should consult with a physician in conjunction with any pregnancy test, positive or negative.

Orthodox medical protocol

The pregnancy test is usually done 14–16 days after egg retrieval. Pregnancy status can be checked by a home urine pregnancy test, or patients can have their blood beta-hCG levels tested at their ART clinic. Pregnancy is confirmed if beta-hCG levels are ≥ 5 IU/L.137

If the pregnancy test is positive, a transvaginal ultrasound scan is usually carried out between 6 and 7 weeks’ gestation to assess viability of the pregnancy. If the pregnancy is viable, patients are often discharged from the ART clinic, and usual obstetric care is initiated by the patient’s GP.

Some patients may not be discharged from the ART clinic until later, for example, if they need immunotherapy. In some cases a specialist referral is necessary, for example, in patients testing positive for thyroid antibodies. It is important for fertility acupuncturists to monitor and to assist patients and ensure that appropriate referrals have been made.

Home Testing

Pregnancy tests, based on human chorionic gonadotropin (hCG) immunoassay, are commonly used in the home. They may be purchased from pharmacies and, in many countries, in supermarkets. The technology required to deliver a foolproof test to an untrained user is similar to that used in POC testing by medical professionals, based on lateral flow immunochromatography, with a visual end point and a control indication (see Lateral Flow Immunoassay Systems; Lateral Flow and Consumer Diagnostics). Recently, visual cues, which were often misinterpreted, have been replaced by digital displays, e.g., indicating the text message Pregnant with an estimate of the number of weeks since conception. Home tests are also available for ovulation monitoring and cardiac assessment. The technology exists to provide home tests for a wider variety of analytes, subject to market demand. It is important to make the distinction between these tests and the glucose or anticoagulant tests performed at home that are supplied under prescription with the appropriate medical backup.

Tests

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Pregnancy test

FSH, luteinizing hormone (LH), estradiol

Two FSH levels in the menopausal range of over 40 mlU/ml measured at least 1 month apart are diagnostic of POP

LH is typically elevated

Estradiol levels are low

Technical Note

In some cases, women with POP have spontaneous follicular activity, which may result in erroneous laboratory results. If the index of suspicion for POP is high, the tests are repeated within a couple of months.

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Additional testing may include the following:

Standard blood chemistry–fasting glucose, electrolytes, and creatinine

Karyotyping

Test for fragile X chromosome (FMRl premutation)

Thyroid-stimulating hormone (TSH)

Antithyroid peroxidase antibody

Serum adrenal antibodies

Screen for other autoimmune disorders

Bone density by dual-energy x-ray absorptiometry (DEXA) scan

Screen and test for exposure to environmental and other toxins

Ovarian biopsy and ultrasound are not recommended in this diagnostic evaluation