Pregnancy tests look for hCG (human chorionic gonadotropin) which is excreted in pregnancy. You can detect hCG in either blood or urine pregnancy tests. Which type of pregnancy test your doctor or midwife requests will depend on what they are looking for with your pregnancy.
If it is merely to confirm that you are pregnant, a urine pregnancy tests or home pregnancy test will suffice. If your practitioner has a reason to suspect multiple pregnancies, ectopic pregnancy or a miscarriage, a blood pregnancy test is more often used. Sometimes you will have these blood tests repeated to watch for a rise in the hCG levels.
The rate of rise for hCG in pregnancy is that it nearly doubles about every 48 hours in the first 30 days after implantation, about 7 weeks gestation, though this can vary. After that, the rate of rise begins to slow. hCG levels peak at about 8–10 weeks, then slowly decrease until they level out at about 20 weeks and stay constant for the rest of pregnancy.
HCG Levels in Pregnancy
Most women will never know their hCG levels in pregnancy. Typically a urine test for the mere presence of hCG alone is sufficient for your obstetrical care in pregnancy. Looking at the specific levels is done if there is a complication or a suspected complication.
Common reasons to do a blood test can include concern over the loss of the pregnancy (as in a suspected miscarriage, or ectopic pregnancy), previous pregnancy loss (pregnancy surveillance), or as a part of an effort for some other medical treatment.
It is fairly common to look for pregnancy prior to any major medical procedure or medical procedure that requires anesthesia. I was surprised at how many times the oral surgeon I once worked for got to diagnose a pregnancy.
Some women are surprised that they don’t know or don’t need to know the exact number for their hCG. This may be because they have hung around people before who did need to know this info.
“My friends who had all been pregnant before me were asking me what my hCG numbers were. I didn’t know the levels,” says one mother.
“That made me panic and I called my obstetrician to ask, thinking, maybe they’d told me and I’d forgotten. The nurse reassured me that I didn’t need to know because my pregnancy was healthy. Later the doctor left a message saying that we could do the lab work if I really wanted to know, but why bother? It probably would have just made me crazy.”
Having your hCG levels checked in pregnancy is rarely a one-time thing. Typically if you are having your hCG levels checked, they will be checked repeatedly to look for a change in the numbers. For a healthy pregnancy, they should rise at a certain rate, and if you are monitoring them after a pregnancy loss, you should expect them to go down at a certain rate until they reach zero.
Your doctor or midwife will be a great resource in helping you interpret the numbers.
- Frye A. Understanding Diagnostic Tests in the Childbearing Year. 6th edition. Portland, OR: Labrys Press, 1997.
- Gabbe S, Niebyl J, Simpson JL. Obstetrics: Normal and Problem Pregnancies. 6th Edition. Philadelphia: Elsevier/Saunders, 2012
By Robin Elise Weiss, PhD, MPH
Robin Elise Weiss, PhD, MPH is a professor, author, childbirth and postpartum educator, certified doula, and lactation counselor.
