A Hysterosalpingography (HSG) is a routine diagnostic procedure used during a fertility evaluation. This specialized X-ray test assesses the structural integrity of the uterine cavity and determines if the fallopian tubes are open, or patent. The procedure involves injecting a liquid contrast medium through the cervix into the reproductive tract, allowing a radiologist to visualize the internal structures as the fluid moves under fluoroscopy. While its main purpose is diagnostic, evidence suggests the procedure may unintentionally enhance the chances of conception. This article investigates the evidence behind the observed link between an HSG and increased pregnancy rates and explores the potential biological mechanisms responsible for this phenomenon.
Understanding the HSG Procedure
The HSG is an outpatient imaging test that uses X-rays to generate images of the uterus and fallopian tubes. During the procedure, a thin catheter is inserted through the vagina and cervix into the uterus, and a contrast fluid is gently injected. The fluid fills the uterine cavity, outlining its shape, and then travels into the narrow fallopian tubes.
If the fallopian tubes are open, the contrast medium spills out of the ends of the tubes into the abdominal cavity, confirming patency. If the fluid meets a blockage, its flow is interrupted. The diagnostic goal is to identify common issues that impede natural conception, such as scar tissue, polyps, or blockages within the tubes. This assessment of tubal patency is essential for diagnosing female infertility.
The Observed Link to Increased Pregnancy Rates
A temporary increase in conception rates occurs in the months immediately following an HSG. This positive effect is particularly noticeable in women diagnosed with unexplained infertility. The improved odds of pregnancy are generally considered a beneficial side effect rather than the primary reason for performing the test.
Research indicates that the boost in fertility typically occurs within the first three to six menstrual cycles after the procedure. For instance, some findings suggest that the chance of pregnancy may increase by up to 30% within the first three months following the test in certain patient populations. This statistical observation reinforces the idea that the mechanical act of flushing the tubes may offer a therapeutic benefit for some couples.
Biological Mechanisms for Fertility Enhancement
The therapeutic effect of the HSG is largely attributed to the mechanical action of the fluid passing through the reproductive tract, often described as “tubal flushing.” This flushing action is hypothesized to clear the way for sperm and egg transport, addressing subtle barriers to fertilization. One proposed mechanism is the dislodgement of minor obstructions, such as small mucous plugs, cellular debris, or small particulate matter, that may be silently blocking the fallopian tube lumen.
The pressure created by injecting the contrast medium may also mechanically stretch the walls of the fallopian tubes. This stretching could help to gently break down mild adhesions or resolve functional spasms, restoring the full diameter of the tube. Furthermore, the procedure may wash away inflammatory substances that could negatively impact sperm, egg, or embryo function, creating a more favorable physiological environment for conception.
Does the Type of Contrast Medium Matter?
The contrast medium used during the HSG procedure is a factor in determining the post-procedure fertility boost. There are two main types of contrast agents: water-soluble and oil-soluble. While both are effective for checking tubal patency, studies suggest that oil-soluble contrast media are associated with a more pronounced and sustained increase in pregnancy rates.
A major randomized trial found that women who received oil-based contrast had a significantly higher rate of ongoing pregnancy and live birth compared to those who received water-based contrast. Clinical pregnancy rates were 40% in the oil-based group versus 29% in the water-based group within a six-month follow-up period. The oil-based media are more viscous and are thought to provide a better, more thorough flushing action superior at dislodging debris. This difference suggests that the physical properties of the medium, not just the mechanical pressure, play a large part in the therapeutic outcome.