How to Determine Whether You’re Pregnant

By Joanne Stone, Keith Eddleman, Mary Duenwald

Well, are you or aren’t you? These days, you don’t need to wait to get to your practitioner’s office to find out whether you’re pregnant. You can opt instead for self-testing. Home tests are urine tests that give simply a positive or negative result. (By the way, these tests are very accurate for most people.)

Your practitioner, on the other hand, may perform either a urine test similar to the one you took at home or a blood test to find out whether you’re pregnant.

Getting an answer at home

Suppose you notice some bloating or food cravings, or you miss your period by a day or two. You want to know whether you’re pregnant, but you aren’t ready to go to a doctor yet. The easiest, fastest way to find out is to go to the drugstore and pick up a home pregnancy test.

These tests are basically simplified chemistry sets, designed to check for the presence of human chorionic gonadotropin (hCG, the hormone produced by the developing placenta) in your urine. Although these kits aren’t as precise as laboratory tests that look for hCG in blood, in many cases they can provide positive results very quickly — by the day you miss your period, or about two weeks after conception.

The results of home pregnancy tests aren’t a sure thing. If your test comes out negative but you still think you’re pregnant, retest in another week or make an appointment with your doctor. A urine test is positive at a level of about 20–50 IU/L while a blood test is positive at a level of 5–10 IU/L, depending on the test.

So a blood test will be positive a little earlier than a urine test. An ultrasensitive blood test can even detect an hCG level of about 1–2 IU/L. hCG is found in the maternal blood at 6–12 days after ovulation (20–26 days from last menstrual period of ovulation occurs on day 14).

Going to your practitioner for answers

Even if you had a positive home pregnancy test, most practitioners want to confirm this test in their office before beginning your prenatal care. Your practitioner may decide to simply repeat a urine pregnancy test or to use a blood pregnancy test instead.

A blood pregnancy test checks for hCG in your blood. This test can be either qualitative (a simple positive or negative result) or quantitative (an actual measurement of the amount of hCG in your blood). The test your practitioner chooses depends on your history and your current symptoms and on her own individual preference. Blood tests can be positive, even when urine tests are negative.

Calculating your due date

Only 1 in 20 women actually delivers on her due date — most women deliver anywhere from three weeks early to two weeks late. Nonetheless, it’s important to pinpoint the due date as precisely as possible to ensure that the tests you need along the way are performed at the right time. Knowing how far along you are also makes it easier for your doctor to see that the baby is growing properly.

The average pregnancy lasts 280 days — 40 weeks — counting from the first day of the last menstrual period. Your due date — what doctors once referred to as the EDC, for estimated date of confinement (in the old days, women were actually “confined” to the hospital around the time of their delivery) — is calculated from the date on which your last menstrual period (LMP) started.

If your cycles are 28 days long, you can use a shortcut to determine your due date. Simply subtract three months from your LMP and add seven days. If your last period started on June 3, for example, your due date would be March (subtract three months) 10 (add seven days).

If your periods don’t follow 28-day cycles, don’t worry. You can establish your due date in other ways. If you’ve been tracking ovulation and can pinpoint the date of conception, add 266 days to that date (the average time between the first day of your LMP and ovulation is about 14 days, or 2 weeks).

If you’re unsure of the date of conception or the date your last period started, an ultrasound exam during the first three months can give you a good idea of your due date. A first-trimester ultrasound predicts your due date more accurately than a second- or third-trimester one.

You can also use a pregnancy wheel to calculate how far along you are. To use this handy tool, line up the arrow with the date of your last menstrual period and then look for today’s date. Just below the date you see the number of weeks and days that have gone by.

(If you know the date of conception, rather than your last period, there is a line on the wheel corresponding to this, too.) There are now online wheels as well as apps that you can download to calculate your due date.