How to rule out pregnancy

How to Rule Out Pregnancy

To rule out pregnancy with high accuracy, a healthcare provider can be reasonably certain a woman is not pregnant if she has no symptoms or signs of pregnancy and meets any ONE of six specific criteria established by the CDC. 1

Criteria for Ruling Out Pregnancy

A healthcare provider can be reasonably certain that a woman is not pregnant if she has no symptoms or signs of pregnancy and meets any ONE of the following criteria:

• Is ≤7 days after the start of normal menses
• Has not had sexual intercourse since the start of last normal menses
• Has been correctly and consistently using a reliable method of contraception
• Is ≤7 days after spontaneous or induced abortion
• Is within 4 weeks postpartum
• Is fully or nearly fully breastfeeding (≥85% of feeds are breastfeeds), amenorrheic, and <6 months postpartum

These criteria have a negative predictive value of 99-100% for ruling out pregnancy 1.

Pregnancy Testing

When the above criteria cannot be met, pregnancy testing should be considered:

• Urine pregnancy tests detect human chorionic gonadotropin (hCG) and are widely available
• Most FDA-approved qualitative tests have a sensitivity of 20-25 mIU/mL in urine 1
• Pregnancy can be detected as early as 3-4 days after implantation (which occurs 6-8 days after fertilization) 2
• By 7 days after a missed period, 98% of pregnancies can be detected with current test kits 2

Important limitations of pregnancy tests:

• Cannot detect pregnancies resulting from very recent intercourse
• May require additional time beyond a missed period for 100% accuracy (up to 11 days after expected menses) 1
• May show positive results for several weeks after pregnancy termination (delivery or abortion) 1
• Early pregnancy urine contains high levels of hyperglycosylated hCG (H-hCG), which some home tests detect poorly 3

Definitive Confirmation of Pregnancy

For definitive confirmation of pregnancy, healthcare providers should look for positive signs including:

• Detection of hCG in maternal serum or urine
• Visualization of the fetus via ultrasound (can detect a gestational sac as early as 4-5 weeks)
• Fetal heart sounds (detectable via Doppler ultrasound at 8-10 weeks)
• Fetal movements felt by an examiner (after 20 weeks)
• Palpation of fetal parts (usually possible after 20 weeks) 4

Algorithm for Ruling Out Pregnancy

1. First step: Assess if patient meets any of the six criteria for reasonably excluding pregnancy

   • If YES → pregnancy is highly unlikely (99-100% negative predictive value)
   • If NO → proceed to testing

2. Second step: Determine timing relative to potential conception

   • If >7 days after missed period → urine pregnancy test is highly reliable
   • If <7 days after missed period or uncertain timing → consider blood hCG test (more sensitive)

3. Third step: Interpret test results

   • Negative test + meets criteria → pregnancy ruled out
   • Negative test + does not meet criteria → consider repeat testing in 1-2 weeks
   • Positive test → pregnancy confirmed

Special Considerations

• For women who had recent (within 5 days) unprotected intercourse, consider offering emergency contraception if pregnancy is not desired 1
• Emergency contraception with levonorgestrel is most effective when taken as soon as possible after unprotected sex and works within 72 hours (3 days) 5
• A negative pregnancy test 1 week after a missed period virtually guarantees that the woman is not pregnant 2
• In cases of amenorrhea without pregnancy, further evaluation for other causes should be considered 6

Common Pitfalls to Avoid

• Relying solely on a negative pregnancy test when the woman does not meet any of the six criteria
• Testing too early after potential conception (may yield false negative)
• Failing to consider the limitations of home pregnancy tests, which vary widely in sensitivity (6.3-50 IU/L) 3
• Overlooking that 60% of home pregnancy tests have poorer detection of H-hCG, the predominant form in early pregnancy 3
• Assuming breastfeeding alone prevents pregnancy without meeting the specific criteria (fully/nearly fully breastfeeding, amenorrheic, <6 months postpartum)

By following these evidence-based guidelines, healthcare providers can accurately rule out pregnancy before initiating contraception or other treatments that may be contraindicated in pregnancy.