Preterm labour: confirming rupture of membranes: practice question

A OBG question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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OBG · Preterm labour: confirming rupture of membranes

Sample item

A woman at 33 weeks reports a gush of fluid. Sterile speculum shows pooling and a nitrazine paper that turns deep blue. In which situation would a deep blue nitrazine result be misleading?

AContamination with urineBContamination with blood, semen or bacterial vaginosis dischargeCPresence of normal acidic vaginal secretionsDPresence of sweat

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Contamination with blood, semen or bacterial vaginosis discharge

Nitrazine paper turns blue above pH 6.5, and amniotic fluid has pH 7.0 to 7.5, whereas normal vaginal pH is 4.5 to 5.5. Alkaline contaminants such as blood, semen, alkaline antiseptics and the discharge of bacterial vaginosis give false positives. Digital examination should be avoided and pooling plus ferning or a biochemical test used for confirmation.

Option by option

A. Contamination with urine
Urine is usually acidic or neutral and rarely gives a false positive in this way.
B. Contamination with blood, semen or bacterial vaginosis discharge (correct)
Correct. These alkaline contaminants can falsely turn nitrazine blue.
C. Presence of normal acidic vaginal secretions
Normal acidic secretions would give a negative, not false positive, result.
D. Presence of sweat
Sweat is not a relevant cause of false results.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this OBG question

What is the answer to this OBG question?

The best answer is B, Contamination with blood, semen or bacterial vaginosis discharge. Nitrazine paper turns blue above pH 6.

Why is "Contamination with urine" not the answer?

Urine is usually acidic or neutral and rarely gives a false positive in this way.

Why is "Presence of normal acidic vaginal secretions" not the answer?

Normal acidic secretions would give a negative, not false positive, result.

Why is "Presence of sweat" not the answer?

Sweat is not a relevant cause of false results.

What concept does this question test?

It tests Preterm labour: confirming rupture of membranes in OBG. 5, and amniotic fluid has pH 7.0 to 7.5, whereas normal vaginal pH is 4.5 to 5.5. Alkaline contaminants such as blood, semen, alkaline antiseptics and the discharge of bacterial vaginosis give false positives. Digital examination should be avoided and pooling plus ferning or a biochemical test used for confirmation.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Preterm labour: confirming rupture of membranes?

Learn management algorithms as steps: PPH, eclampsia, ectopic pregnancy. Then use the flashcards and the other OBG questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.