First Trimester: Pregnancy Test (hCG)
If pregnancy is only suspected, or if the pregnancy test was not performed by a healthcare practitioner (for example, was instead performed with an at-home urine pregnancy test), then a pregnancy test may be done to confirm that a woman is pregnant.
Pregnancy tests measure human chorionic gonadotropin (hCG), a hormone that is produced by the placenta when a woman is pregnant. The amount of hCG produced during pregnancy increases steadily during the first trimester (8-10 weeks) of a normal pregnancy, peaking around the 10th week after the last menstrual cycle.
- Qualitative tests can be done on either urine or blood; they are usually done after a missed menstrual period to confirm that the woman is indeed pregnant.
- Quantitative tests measure the actual level of hCG and are performed on blood samples. Some laboratories may have targets for what the hCG level should be for each week of gestation during the first trimester, but each woman's levels may vary (and the exact gestational age may be uncertain). The most important feature of hCG during the first trimester is that the levels should essentially double every two or three days. If there is any concern about the pregnancy, the patient's healthcare practitioner will often measure quantitative hCG levels several times to make sure that they are increasing at an appropriate rate.
If hCG levels are not rising normally, the cause may be an ectopic pregnancy (in which the pregnancy is occurring within the tube that leads from the ovary to the uterus or, more rarely, in the abdominal cavity) or an abnormal intra-uterine pregnancy. Ectopic pregnancy may become a medical emergency, so practitioners may need to perform vaginal ultrasound in patients whose hCG is not rising appropriately to make sure that there is a gestational sac within the uterus.