Pregnancy Test

General Description

A pregnancy test is performed to confirm whether a patient is pregnant. The goal is to detect the presence of human chorionic gonadotropin (hCG) in the blood or urine. This hormone is produced when an egg has been fertilized and is therefore only found in the bodies of pregnant women. The concentration of hCG increases very rapidly during the first 10 weeks of pregnancy, almost doubling every 48 hours.

Generally, the patient takes an over-the-counter urine test at home, and if the result is positive, she visits a doctor to confirm the pregnancy through a blood test and a transvaginal ultrasound. The blood test is more sensitive than the urine test because it detects lower levels of hCG: to confirm a pregnancy with a urine test, 20 mIU/ml (milli-international units per milliliter) of hCG are required, whereas a blood test can detect it with just 5 mIU/ml.

There are two types of blood pregnancy tests:

• Qualitative: Confirms the presence of hCG hormone.
• Quantitative: Measures the concentration of hCG hormone present.

The transvaginal ultrasound, on the other hand, is a diagnostic test that allows visualization of the pelvic cavity using ultrasound waves.

When is it indicated?

For a pregnancy test, whether urine or blood, to be truly reliable, it should be performed 14 to 15 days after fertilization or after a delay of three to four days in menstruation. However, a blood test can already confirm or rule out pregnancy as early as six to nine days after fertilization. If done earlier than this period, a false negative may occur—meaning the pregnancy exists, but there has not been enough time to detect an adequate amount of hCG.

Additionally, the quantitative test is used to monitor pregnancy development during the first two months of gestation:

• An hCG level that does not rise adequately may indicate a pregnancy problem, such as a miscarriage or an ectopic pregnancy (outside the uterus).
• An excessively high hCG level may indicate the presence of a multiple pregnancy or a molar pregnancy (abnormal growth of placental cells that prevents normal fetal development).

The transvaginal ultrasound, on the other hand, is performed between the sixth and ninth weeks of gestation. It confirms the pregnancy by detecting the amniotic sac and can also determine gestational age and identify different conditions such as ectopic, anembryonic (without an embryo), or multiple pregnancies.

How is it performed?

A blood pregnancy test involves drawing a blood sample (usually one tube) using a hypodermic needle with an attached syringe. The sample is taken from a vein in the arm.

For a transvaginal ultrasound, a device called an ultrasound scanner is used, which includes a component known as a transducer. The transducer is inserted into the patient’s vagina and moved around the area while emitting ultrasound waves. These sound waves bounce off pelvic organs and tissues, creating echoes that are received by the transducer and sent to a computer, which transforms them into images. These images are displayed in real-time on the ultrasound monitor.

Risks

A transvaginal ultrasound is a simple and safe procedure that poses no risk to the patient. In the case of a blood test, the only possible complication is the formation of a small bruise at the site where the needle is inserted.

What to expect from a pregnancy test

The blood pregnancy test is performed with the patient seated and their arm extended. The doctor locates the vein where the puncture will be made (usually on the inner side of the elbow), places an elastic band above the puncture site to facilitate vein filling, and disinfects the area with a sterile gauze soaked in alcohol. It is normal to feel mild pain when the needle is inserted. Once the blood is drawn, a bandage is applied, and gentle pressure is exerted to stop the bleeding. The procedure is completed in a few minutes.

Before starting the ultrasound, the patient must remove clothing from the lower body, put on a hospital gown, and empty her bladder. She then lies on her back on the examination table with her legs flexed. Before insertion into the vagina, the transducer is covered with a disposable latex protector and a layer of lubricating gel is applied to facilitate insertion. Although the transducer is small, mild discomfort may be felt during the examination. The study lasts approximately 15 minutes. Once completed, the patient can resume her daily activities as usual. Some vaginal discharge may occur in the following hours due to the use of lubricating gel, but it is minimal and not a cause for concern.

Medical specialties that request a pregnancy test

Pregnancy tests are requested in the following specialties:

• Primary Care
• Gynecology and Obstetrics
• Assisted Reproduction