Pregnancy Testing - Sexual Health Peer Resource Center

As mentioned before, pregnancy tests work by detecting the hormone human chorionic gonadatropin (HCG), a hormone relased by the developing embryo, in the blood or urine of a woman. Different types of tests have different sensitivities; in other words, they can accurately detect pregnancy at different stages of gestation. Some tests are accurate as soon as 10 days after conception, while others may be negative for up to several weeks after conception. It is important to understand the sensitivity of the test performed, and to return for a retest if a normal period does not occur within two weeks.

Available Tests (appropriate for referrals at Stanford):

Vaden Student Health Center
- Urine testing is available every day (even weekends and holidays through same day emergency care), as often as the patient desires.
- All testing at Vaden is free to Stanford students.
- No appointment is necessary for a pregnancy test, however one can be made.
- Following each test, a brief consultation with a doctor or a nurse practitioner will occur, in order to discuss the results of the test (the results take approximately five minutes to read).
- Urine tests at Vaden are accurate 14 days after intercourse.
- Blood tests can be accurate 10 days after intercourse, but may only be ordered by a nurse or a physician in the case of special circumstances (such as potential ectopic pregnancies). Blood tests are not used for ordinary early diagnosis tests.
- The first urine specimen of the morning is best for the test (urine is more concentrated after sleep), so a sample should be collected as early in the day as possible in a small, clean container (provided by the nurses).
Planned Parenthood
- HCG urine test can be given after a missed period, or 14 days after intercourse
- Urine tests range in price from $10-$20; no appointment is necessary
- Blood tests can be given 10 days after intercourse, however they are more expensive and some Planned Parenthood offices do not have adequate blood testing facilities and thus will have to send blood samples away to an outside lab (thus results will take at least 24 hours).
Home Pregnancy Tests
- These are urine tests that look for the same HCG hormone that clinical tests do
- These tests can be purchased at any grocery store, pharmacy, or Walmart-type location
- Advantages include privacy, convenience, easy instructions, and anonymity
- While fairly accurate, false negatives can result from tests performed too early for pregnancy to be detected or from urine that is too dilute
- Should test result in a positive, the private home environment does not provide the same clinical or counseling services that are available at either Vaden or Planned Parenthood
Private Physicians
- Procedures and costs vary

Additional Information

If you have a negative pregnancy test and are still going to have intercourse, you should use contraception. Even if you believe you are pregnant (i.e. you don’t believe the test results), continue to use or start to use birth control if you do not wish to become pregnant.

Although pregnancy tests are quite accurate, false positives and false negatives may occur for several reasons:

False Positives: human error, LH cross reaction, drug interference
False Negatives: human error, test performed too early in pregnancy, urine too dilute to detect HCG, drug interference

For these reasons, careful follow up with a health care provider is an important part of any pregnancy test.

Where in the female reproductive system does fertilization usually occur?

In the first 1/3 of the fallopian tube.

When during a woman’s menstrual cycle is she fertile? For how many days (approximately) is she fertile?

Usually fertilization occurs 12-24 hours after ovulation, in the middle of a woman’s cycle. An egg lives for 24 hours after it is released. Sperm can live for at least 3 days in a woman’s body.

Upshot: A woman is fertile for approximately FOUR days, BUT it is very difficult to tell when those days are. Ovulation and menstrual cycles change with stress, travel, sickness, and many other factors. She should still protect herself ever time she has sex!

Look on the next page for a further explanation of fertility charting (a more exact way of knowing which four days a woman is fertile).


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	General Pregnancy Pregnancy Testing Infertility	Pregnancy Testing As mentioned before, pregnancy tests work by detecting the hormone human chorionic gonadatropin (HCG), a hormone relased by the developing embryo, in the blood or urine of a woman. Different types of tests have different sensitivities; in other words, they can accurately detect pregnancy at different stages of gestation. Some tests are accurate as soon as 10 days after conception, while others may be negative for up to several weeks after conception. It is important to understand the sensitivity of the test performed, and to return for a retest if a normal period does not occur within two weeks. Available Tests (appropriate for referrals at Stanford): Vaden Student Health Center Urine testing is available every day (even weekends and holidays through same day emergency care), as often as the patient desires. All testing at Vaden is free to Stanford students. No appointment is necessary for a pregnancy test, however one can be made. Following each test, a brief consultation with a doctor or a nurse practitioner will occur, in order to discuss the results of the test (the results take approximately five minutes to read). Urine tests at Vaden are accurate 14 days after intercourse. Blood tests can be accurate 10 days after intercourse, but may only be ordered by a nurse or a physician in the case of special circumstances (such as potential ectopic pregnancies). Blood tests are not used for ordinary early diagnosis tests. The first urine specimen of the morning is best for the test (urine is more concentrated after sleep), so a sample should be collected as early in the day as possible in a small, clean container (provided by the nurses). Planned Parenthood HCG urine test can be given after a missed period, or 14 days after intercourse Urine tests range in price from $10-$20; no appointment is necessary Blood tests can be given 10 days after intercourse, however they are more expensive and some Planned Parenthood offices do not have adequate blood testing facilities and thus will have to send blood samples away to an outside lab (thus results will take at least 24 hours). Home Pregnancy Tests These are urine tests that look for the same HCG hormone that clinical tests do These tests can be purchased at any grocery store, pharmacy, or Walmart-type location Advantages include privacy, convenience, easy instructions, and anonymity While fairly accurate, false negatives can result from tests performed too early for pregnancy to be detected or from urine that is too dilute Should test result in a positive, the private home environment does not provide the same clinical or counseling services that are available at either Vaden or Planned Parenthood Private Physicians Procedures and costs vary Additional Information If you have a negative pregnancy test and are still going to have intercourse, you should use contraception. Even if you believe you are pregnant (i.e. you don’t believe the test results), continue to use or start to use birth control if you do not wish to become pregnant. Although pregnancy tests are quite accurate, false positives and false negatives may occur for several reasons: False Positives: human error, LH cross reaction, drug interference False Negatives: human error, test performed too early in pregnancy, urine too dilute to detect HCG, drug interference For these reasons, careful follow up with a health care provider is an important part of any pregnancy test. Where in the female reproductive system does fertilization usually occur? In the first 1/3 of the fallopian tube. When during a woman’s menstrual cycle is she fertile? For how many days (approximately) is she fertile? Usually fertilization occurs 12-24 hours after ovulation, in the middle of a woman’s cycle. An egg lives for 24 hours after it is released. Sperm can live for at least 3 days in a woman’s body. Upshot: A woman is fertile for approximately FOUR days, BUT it is very difficult to tell when those days are. Ovulation and menstrual cycles change with stress, travel, sickness, and many other factors. She should still protect herself ever time she has sex! Look on the next page for a further explanation of fertility charting (a more exact way of knowing which four days a woman is fertile).