Checking the tubes, and the test that turned out to be a treatment
Which contrast fluid is used changes your chance of a live birth.
The tube test, hysterosalpingography, involves passing contrast fluid through the uterus and tubes while taking images. There are two kinds of contrast, oil-based and water-based, and for decades the choice was treated as a technical preference.
Then 1,119 women across 27 Dutch hospitals were randomly assigned to one or the other.
| Outcome within 6 months | Oil contrast | Water contrast | Effect |
|---|---|---|---|
| Live birth | 214 of 552 (38.8%) | 155 of 552 (28.1%) | Rate ratio 1.38 (95% CI 1.17 to 1.64) |
| Ongoing pregnancy | 220 of 554 (39.7%) | 161 of 554 (29.1%) | Rate ratio 1.37 (95% CI 1.16 to 1.61) |
That is an absolute difference of 10.7 percentage points, or about one extra live birth for every nine to ten women flushed with oil instead of water. Adverse events were low and similar in both groups.
The same women were followed for five years. The advantage narrowed but did not vanish: live birth 74.8% with oil against 67.3% with water, and the time to an ongoing pregnancy was 10.0 months against 13.7. The most likely reading is that oil contrast moves some conceptions earlier and leaves a smaller real advantage at the end.
A pooled analysis of six trials in 2,562 patients found an advantage for oil contrast on ongoing pregnancy, odds ratio 1.47 (95% CI 1.12 to 1.93), with no difference in miscarriage or ectopic pregnancy. The three trials reporting live birth could not be pooled because they varied too much, which is worth stating rather than hiding.