When should I take a home pregnancy test?

Many home pregnancy tests claim to be able to tell whether you're pregnant as early as the first day of a missed period. Some claim you can take them even before that point. But home pregnancy test results are more likely to be accurate if they are taken after the first day of a missed period. That's because shortly after a fertilized egg attaches to the uterine lining — a process called implantation — the placenta begins forming. The placenta makes the pregnancy hormone human chorionic gonadotropin (HCG). HCG can be found in blood and urine. HCG is present in the body only during pregnancy.

A home pregnancy test checks to see if there's HCG in the urine. During early pregnancy, the amount of HCG in blood and urine rises quickly — doubling every 2 to 3 days. That means if you wait a day or two after your missed period to take the test, and you are pregnant, it's more likely the test will find HCG and show a positive result.

The timing of ovulation makes a difference in the accuracy of a home pregnancy test. And ovulation can change from month to month. A fertilized egg also can implant in the uterus at different times. That can affect the timing of when HCG starts to be made and when it can be found with a home pregnancy test. Irregular menstrual cycles also can affect pregnancy test results, as they make it hard to figure out when a period should start.