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Make the Diagnosis: Early Pregnancy

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Prior Probability

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The probability of pregnancy varies, depending on the clinical situation. In the emergency department, the prevalence of unsuspected pregnancy is 6.3%. The prevalence increased to 13% in women with abdominal or pelvic complaints.7 Among women trying to get pregnant, the probability of pregnancy after a single episode of unprotected sexual intercourse approximates 20% to 33%.8

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Population for Whom Pregnancy Should Be Considered

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  • All women of childbearing years with an intact uterus who are sexually active and who have missed their last menstrual period or had an abnormal menstrual period.

  • Any woman who wonders whether she might be pregnant.

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Detecting the Likelihood of Pregnancy

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General symptoms of early pregnancy include amenorrhea, morning sickness, and tender or tingling breasts. In the original review, the range of likelihood ratios (LRs) for women reporting a delayed menses was 1.0 to 2.1 and 0.25 to 0.99 for women reporting their menses on time. For women reporting morning sickness or any pregnancy symptoms, the LR was 2.7 or 2.4, respectively. Another indicator of early pregnancy is whether the woman thinks she is pregnant. When a woman thinks there is a chance she is pregnant, the LR for pregnancy is 2.1 (95% CI, 2.0-2.2); if she thinks she is not pregnant, the LR is 0.35 (95% CI, 0.31-0.39). Physical examination findings, such as an enlarged uterus with a soft cervix or a palpable uterine artery, have been studied and may be useful in some clinical settings.

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Reference Standard Test

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To establish a diagnosis of early pregnancy, a clinician should order a urine or serum HCG test.

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Original Article: Is This Patient Pregnant?

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Clinical Scenarios

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Are These Patients Pregnant?
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For each of the following cases, the clinician may need to determine the probability that the patient is pregnant.

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Case 1
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A 36-year-old woman telephones her primary care physician, complaining of symptoms consistent with uncomplicated sinusitis. Before treating her with an antibiotic, you ask her about the possibility of pregnancy; she states her last menstrual period was 3 weeks ago and she is not pregnant.

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Case 2
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A sexually active 16-year-old girl requests birth control pills and asks during the pelvic examination, when her mother has stepped out of the room, if you can tell whether she is pregnant. Her last menstrual period was 8 weeks ago, her home pregnancy test result was negative, and findings on her pelvic examination were normal.

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Case 3
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A 41-year-old woman presents with breast tenderness, and her last menstrual period was 6 weeks ago. She wants to know whether she is “going through the change.”

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