One of the first things you might want to know once you see a positive pregnancy test is whether you're going to have one baby, two, or maybe even more. The thought of carrying multiple babies can elicit a wide range of emotions: excitement, shock, fear, happiness, and all sorts of other feelings.
Human chorionic gonadotropin (hCG) is a hormone only produced during pregnancy to support the growing baby.
HCG levels vary widely from person to person, but follow a predictable pattern throughout pregnancy.
Twins, triplets, and other multiple gestation pregnancies are associated with higher hCG levels, but the lab result is not used to diagnose multiple gestation pregnancies.
A hormone called human chorionic gonadotropin (hCG) is one of the earliest lab tests we have to confirm pregnancy, but can it tell you if you're going to have more than one baby?
What is hCG?
Human chorionic gonadotropin (hCG) is a hormone only produced when a person is pregnant. After conception, the cells quickly start producing hCG. It plays an important role in placental development and helps maintain the pregnancy. When hCG is present in blood or urine samples, pregnancy is confirmed. It is usually detectable 10 days after conception. hCG levels rise predictably throughout the first trimester, then fall and plateau during the second and third trimesters of pregnancy.
In very rare cases, the presence of hCG may indicate a disease process, such as ovarian or testicular cancer. In non-pregnant women, normal hCG levels are less than 5 mIU/ML. In men, the normal level is less than 2 mIU/ML.
Pregnancy tests: Measuring hCG levels
The most common home pregnancy tests detect the presence of hCG in urine. Home blood test kits are also available but require you to prick your finger. You do not receive an hCG level with these tests. Instead, the test is negative (no hCG detected) or positive (hCG present). This is a qualitative test.
The tests done at your healthcare provider's office or sent to a lab are quantitative; they report an actual amount of hCG in your blood or urine sample. It's important to know that results vary widely from person-to-person, week to week, and are not used by themselves to determine your due date.
The importance of hCG levels lies in their trend. Most pregnant people do not need repeated hCG levels. However, if your healthcare provider is concerned about your pregnancy, they may order repeated measurements over a period of time.
Normal HCG levels
During the first trimester, hCG levels rise rapidly, doubling every 2–3 days. As you get closer to the second trimester, those levels will decline and eventually remain stable until you give birth.
The most important aspect of hCG is your personal trend. Most of the time, your healthcare provider won't even order repeated measurements unless they are concerned about serious complications, such as miscarriage or ectopic pregnancy. Ectopic pregnancies occur when the pregnancy develops in your fallopian tubes instead of your uterus, which can lead to medical emergencies.
Can you tell if you're pregnant with twins based on hCG levels?
The short answer is no; hCG levels alone cannot tell you if you're pregnant with twins. This is because so many factors influence hCG levels; no healthcare provider will diagnose twins based on hCG alone.
Studies do show that people pregnant with twins or multiples tend to have hCG levels toward the high end of "normal," but the range is so wide week to week that it just isn't diagnostic. The doubling trend is similar for women pregnant with single or multiple babies.
Diagnosing twin pregnancies
The most reliable method for diagnosing twin pregnancies is an ultrasound. While hCG levels may be higher in twin pregnancies, visualization by ultrasound is the best way to actually see multiple gestational sacs.
Variations in hCG levels during pregnancy
Every woman and every pregnancy is unique. Several factors can influence hCG levels throughout pregnancy. As you've already seen, the "normal" ranges are wide, but extremely high or low levels can indicate pregnancy complications.
High hCG levels
High hCG levels may be the result of the following:
- Multiple gestations (twins, triplets, or more)
- Miscalculated pregnancy dates
- Molar pregnancy, a very rare pregnancy complication
Low hCG levels
Low hCG levels may be the result of the following:
- Miscarriage or a blighted ovum
- Ectopic pregnancy
- Miscalculated pregnancy dates
Other factors that may influence hCG levels include:
- Maternal weight and BMI
- Child gender
- Placental weight
- Presence of hyperemesis gravidarum
As you can see, hCG levels are not one-size-fits-all. It's best to talk with your healthcare provider about your lab results and address any concerns with them.
HCG levels are complicated, variable, and not used for conclusive diagnoses about pregnancy health. Twin and multiple gestation pregnancies are often associated with hCG levels on the higher end of normal. However, your healthcare provider will consider several factors, most notably prenatal ultrasound findings, to determine if you are pregnant with twins.
- StatPearls. Human Chorionic Gonadotropin.
- Fertility and Sterility. What serial hCG can tell you, and cannot tell you, about an early pregnancy.
- European Journal of Epidemiology. Reference ranges and determinants of total hCG levels during pregnancy: the Generation R Study.
- International Journal of Molecular Sciences. hCG: Biological functions and clinical applications.
- Mayo Clinic. Molar pregnancy.