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Pregnancy Tests and Due Dates


The Manual's Editorial Staff

Reviewed/Revised Aug 2022 | Modified Sep 2022
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Pregnancy begins with fertilization (when a sperm enters an egg) and ends with delivery (when the baby is born). Pregnancy lasts about 9 months.

How can I tell if I'm pregnant?

You should suspect you’re pregnant if:

  • Your period is late by a week or more

Symptoms of pregnancy include:

  • Having swollen, tender breasts

  • Feeling sick to your stomach and throwing up

  • Needing to urinate more often than usual

  • Feeling weak and tired

  • Feeling more or less hungry than usual

To find out if you're pregnant, take a pregnancy test. You can buy a test kit at a drug store without a prescription. Or you can get tested at a doctor’s office or clinic.

Home pregnancy tests

A home pregnancy test uses your urine and tests it for a hormone called hCG. Your body makes lots of hCG when you're pregnant. Home pregnancy tests are very accurate.

If your home pregnancy test says you’re not pregnant, but you still think you may be:

  • Wait a few days and do another home pregnancy test

Doctors' pregnancy tests

Doctors usually do the same urine pregnancy test you do at home. But sometimes they test your blood for hCG. The blood test is even more accurate than the urine test. The blood test can tell if you're pregnant even before you miss your period.

Sometimes, doctors do a test to measure the exact amount of hCG in your blood. In the beginning of a pregnancy, your hCG levels usually double every 2 days. Checking your hCG levels several days apart can tell doctors if your pregnancy is developing normally.

When will my baby be born?

Your due date is when your baby is expected to be born. There are 2 ways to figure out your due date:

Your due date is 40 weeks after the first day of your last period. You aren't even pregnant during week one, because the 40 weeks is based on when you had your last period, not when not when a sperm joined or "fertilized" the egg. Usually the pregnancy starts at the end of week two or the beginning of week three, depending on when you ovulate.

It's hard to add 40 weeks, so instead:

  • Take the first day of your last period—say it's April 7

  • Go back 3 months—that's January 7

  • Go ahead 7 days—that's January 14

  • Go ahead 1 year—you're due January 14 next year

Ultrasound can tell just how pregnant you are. Doctors use ultrasound to measure the size and other features of your fetus. This tells them how many weeks your fetus has been developing. That lets them figure out the due date.

Babies are rarely born exactly on their due date, but it's usually close. It's normal for a baby to be born anytime from 3 weeks before the due date to 2 weeks after the due date. Babies born more than 3 weeks before their due date are premature Preterm (Premature) Baby A preterm baby, also called a premature baby, is born too early. A full pregnancy lasts 37 to 40 weeks, so a preterm baby is born anytime before the 37th week of pregnancy. The earlier babies... read more .

How pregnant am I?

It's important to know how far along you are in your pregnancy. Doctors look for different problems and do different things at specific times in your pregnancy. They typically talk about how far along you are in:

  • Weeks

  • Trimesters

Like your due date, the 40 weeks of pregnancy are counted from the first day of your last period. So your doctor might say "You're 20 weeks pregnant."

Doctors also divide the 40 weeks of pregnancy into 3 groups called trimesters.

  • First trimester: weeks 0 to 12

  • Second trimester: weeks 13 to 24

  • Third trimester: weeks 25 to delivery

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