First-Morning Urine (FMU)
Definition - What does First-Morning Urine (FMU) mean?
First-morning urine is the sample of urine that is expelled immediately after waking up in the morning and is recommended for use with most home pregnancy tests. This is because the first urine a pregnant woman produces in a day contains the highest concentration of human chorionic gonadotropin (hCG). Therefore, using the first-morning urine can better predict pregnancy in its early stages when hCG levels are at their lowest.
FertilitySmarts explains First-Morning Urine (FMU)
Home pregnancy tests detect the level of hCG in a woman's urine. In early stages of pregnancy, the concentration of hCG may not be high enough in urine produced throughout the day to detect pregnancy. However, the first-morning urine contains the highest concentration of hCG. As a result, a sample of urine from first thing in the morning is more likely to provide accurate test results in early pregnancy.
Since hCG levels rapidly increase in a developing pregnancy, a urine sample from any time of day can be used to accurately predict pregnancy by the fourth or fifth week. Therefore, a sample of the first-morning urine is most important during testing in early stages of pregnancy.