How PID can lead to infertility and ectopic pregnancy
PID (pelvic inflammatory disease) can scar the tubes carrying an egg to the womb, making conception less likely and tubal ectopic pregnancy (a pregnancy growing in the tube) more likely.
Remember
PID that reaches the tubes can leave them narrowed by scar tissue, with weakened cilia (tiny hairs lining the tube), so the egg is carried poorly. That reduces fertility, meaning conception is less likely, and raises the risk of ectopic pregnancy.
Memory aid
the tube is a tunnel with a conveyor belt of cilia
Picture the tube as a tunnel lined with a conveyor belt: scarring narrows the tunnel and damaged cilia stall the belt, so the egg struggles to get through.
Pelvic inflammatory disease (PID) happens when infection spreads upwards through the female reproductive tract, from its lower part to its upper part. It can reach the uterus and then the fallopian tubes, the narrow tubes that carry an egg from the ovary to the womb.
When infection reaches a tube it causes salpingitis, which means inflammation of the tube. That inflammation can damage the tube in two linked ways. It can leave a stricture, a narrowed, scarred segment. It can also reduce the function of the cilia, the tiny hairs lining the tube that normally waft the egg towards the womb.
The egg is then not carried along effectively. Conception is less likely. A fertilised egg held up in the tube may also implant there instead of reaching the uterus, which is a tubal ectopic pregnancy, a pregnancy growing in the tube.
Most women with PID have only mild symptoms, so the condition can easily be missed and the damage can build up unnoticed. Reduced fertility or an ectopic pregnancy may be how the damage is first noticed. These are possible complications, not certainties, and they can follow if PID is not treated early, so early diagnosis and treatment matter. Because PID raises the risk of a later ectopic pregnancy, a previous episode still matters when a woman has pain or bleeding in early pregnancy, even if the original infection was treated.
Key facts
- Route
- infection spreads upwards through the female reproductive tract, and the symptoms depend on how far it has climbed.
- Salpingitis
- inflammation of a fallopian tube, which can then damage the tube.
- Strictures
- narrowed, scarred segments of the tube, so the egg may not be able to travel along it.
- Cilia
- the tiny hairs lining the tube that normally waft the egg towards the womb; inflammation can reduce their function.
- Ectopic risk
- the same tubal damage also increases the risk of tubal ectopic pregnancy.
- Not inevitable
- reduced fertility and ectopic pregnancy are possible complications that can follow if PID is not treated early.
Exam traps
- Reduced fertility after PID is not down to a body-wide inflammatory response suppressing ovulation, because the damage is local: what fails is the egg's passage along the tube, not the hormonal control of ovulation.
- A tubo-ovarian abscess (a pus-filled collection involving the tube and ovary) is a recognised complication of salpingitis, but the raised ectopic risk is explained by scarring and loss of cilia in the tube, not by loss of ovulation.
- Inflammation in the muscle wall of the uterus is not what is usually blamed for reduced fertility after PID, because the recognised cause is damage to the fallopian tubes.
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