A delay in menstruation from the expected date, particularly in women who usually have regular menstrual cycles and who have recently had unprotected sex (within the last 2-3 weeks), may be the first sign of pregnancy. To be sure, it is necessary to take a pregnancy test. Types of pregnancy tests There are several types of pregnancy tests, which can be divided into two groups: Over-the-counter pregnancy tests , which can be purchased in pharmacies and other shops and are suitable for doing at home; Laboratory tests , which are carried out in a laboratory with specific equipment. All pregnancy tests use a urine sample or a blood sample and all look for (and some also measure) the hormone human chorionic gonadotropin ( HCG ). Over-the-counter tests use urine. Laboratory tests can use a blood sample (collected in the laboratory) and can also be carried out on urine (collected at home or in the laboratory). Over-the-counter tests are not all the same and neither are laboratory tests. Blood tests are more sensitive and specific than urine tests. However, the most common is to do an over-the-counter test, because it is simpler and more convenient. Despite using urine and, therefore, being less sensitive, they do not require a prescription and the results are practically immediate . The important thing is to strictly follow the instructions on the information leaflet because tests are not all the same. Over-the-counter tests are qualitative , that is, their result is positive or negative. Laboratory tests are qualitative and quantitative , that is, in addition to indicating whether the result is positive or negative, the HCG value determined per unit volume of the sample is presented. Are pregnancy test results reliable? The results of pregnancy tests are quite reliable, if the test is carried out at the correct time and the respective instructions are strictly followed . For most tests urine can be collected at any time of the day. There is no need to fast or any other preparation for a pregnancy test. However: Urine should not be collected after drinking a large amount of liquids because it will be more diluted and this could result in a false negative result. If there are specific instructions about the urine to use, for example the first urine in the morning, these instructions should be followed. False positive results are rarer than false negatives . In both urine and blood tests, one of the main causes of false negatives is carrying out the tests too early in relation to conception. What is human chorionic gonadotropin? Human chorionic gonadotropin, also known as HCG or pregnancy hormone, is the hormone searched in pregnancy tests. Its main function is to stimulate the corpus luteum formed after ovulation to produce progesterone to maintain the pregnancy . Human chorionic gonadotropin is produced mainly by cells in the placenta, a temporary organ that only exists during pregnancy. HCG begins to be produced in greater quantities a few days after the egg is fertilized by a sperm (conception), when implantation takes place in the uterus, which happens 6 to 10 days after conception. In the first 8 weeks of pregnancy, HCG values almost double every 24 hours, the maximum value is reached at 10 weeks of pregnancy and from around 16 weeks it stabilizes until the end of pregnancy. After delivery, HCG values begin to decrease and may take up to 2 months to return to levels close to zero. There are other organs that produce human chorionic gonadotropin, but in reduced quantities: the pituitary gland, the liver and the colon. Some diseases are also associated with high HCG levels. If you are going to take a pregnancy test Read carefully and strictly follow the instructions on the package leaflet if you are taking an over-the-counter test. Be sure of the number of days your menstruation is late and/or the date of unprotected sexual intercourse so as not to take the test too early. If you do it too early, there is a greater risk of false negative results. If in doubt, seek for medical care. Source: Betz D, Fane K. Human chorionic gonadotropin. Treasure Island: StatPearls Publishing; 2023. Author : Pedro Oliveira Meet the obstetrics-gynecology clinical team from Hospital da Luz network The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
