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Pregnancy: Likelihood Ratios

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The likelihood ratios of findings for Pregnancy are listed below. See the left navigation bar to change the display.

Pre-Test Probability (Prevalence): %.	Post-Test Probability (Predictive Value): %.	Switch to display mode.
Note that calculating probabilities from more than one** finding is inherently inaccurate because findings are not independent. (For example, using two positive findings that share a common pathogenesis is likely to overestimate the true probability.)

Good Negative Likelihood Ratio
Finding	Result	+LR	-LR
[ + ] Did Not Use Birth Control	+ 0 -	1.5	0.3
Study: JAMA. 1997 Aug 20;278(7):586-91. PMID: 9268281

Poorly Diagnostic Findings
Finding	Result	+LR	-LR
[ + ] Delayed Menses	+ 0 -	1.1	0.8
Study: JAMA. 1997 Aug 20;278(7):586-91. PMID: 9268281
[ + ] Urine beta-hCG		Sensitivity = 97%
7 days after missed period. Most urine b-hCG tests are sensitive to 20 mIU/ml. If sensitivity is at 0.5 mIU/ml then should be sensitive by 7 days after fertilization. Study: JAMA 2001 Oct 10;286(14):1759-61. PMID 11594902
[ + ] Urine beta-hCG		Sensitivity = 90%
on 1st day of missed period. Most urine b-hCG tests are sensitive to 20 mIU/ml. If sensitivity is at 0.5 mIU/ml then should be sensitive by 7 days after fertilization. Study: JAMA 2001 Oct 10;286(14):1759-61. PMID 11594902
[ + ] Home Pregnancy Test		Sensitivity = 75%
Sens = 75% when used by actual patients but up to 91% when used by volunteers. Specificity not assessed but should be very high (~99%). Study: Arch Fam Med 1998 Sep-Oct;7(5):465-9. PMID 9755740

Findings With Unspecified Accuracy
Finding	Result	+LR	-LR
[ + ] Goodell's Sign		No accuracy specified.
softening of the cervix, may be detected by 8 weeks of age Study: JAMA. 1997 Aug 20;278(7):586-91. PMID: 9268281
[ + ] Hegar's Sign		No accuracy specified.
Softening of the lower portion of the corpus of the uterus. May be seen by 6 weeks. Study: JAMA. 1997 Aug 20;278(7):586-91. PMID: 9268281
[ + ] Trans-Vaginal Ultrasound		No accuracy specified.
Gestational sac by 4.5-5 weeks, double decidual sign by 5.5-6 weeks, yolk sac by 5-6 weeks, cardiac activity by 5.5-6 weeks. Trans-abdominal ultrasound would be less sensitive for these findings. Study: UpToDate http://www.utdol.com/online/content/topic.do?topicKey=antenatl/22517