Pregnancy can be detected by three or four weeks gestational age (or one to two weeks after ovulation). If your period is late and you think you may be pregnant, you have two options. The first is to take an at-home urine test with a home pregnancy test. These tests are easy to use (just pee on a stick and wait) and have a 90 percent accuracy rating. Alternatively, you can have your doctor order a blood test (almost 100 percent accuracy).
Both blood and urine pregnancy tests check for the presence of a chemical called human chorionic gonadotropin, which is produced during a pregnancy. Waiting two weeks post conception (one the first day of a missed period) is recommended, but positive results can be detected as early as one week after conception.
After a pregnancy has been detected by a blood or urine test, your doctor will request an ultrasound to confirm that a live embryo is present. Ultrasounds can first be seen at five weeks pregnancy and an embryo and heart beat can be detected by six weeks. Pregnant women who aren’t experiencing any problems will usually have their first ultrasound around three months.
Peter Doubilet and Carol Benson are a married couple with five grown children between them. They teach and see patients at the Brigham and Women's Hospital in Boston where Peter is Senior Vice Chair of Radiology and Carol is Director of Ultrasound and Co-Director of High Risk Obstetrical Ultrasound. Together they have written Your Developing Baby (McGraw-Hill, 2008).