What Causes Pelvic Congestion Syndrome? Ovarian Vein Reflux, Pregnancy and Hormones

So, what causes pelvic congestion syndrome? In short, blood flows the wrong way in the veins of the pelvis and pools there. Most often this is because the one-way valves in the ovarian veins have failed. Pregnancy, hormones, inherited vein weakness and, less often, a squeezed vein higher up all play a part. This guide explains each cause in plain terms and who is most at risk.

How pelvic veins normally work

Blood from the womb, ovaries and other pelvic organs drains into a web of small veins on each side of the womb. From there it leaves the pelvis in two main ways:

• Upwards, through the two ovarian veins. The left ovarian vein empties into the left kidney (renal) vein. The right ovarian vein empties straight into the main vein of the abdomen, the inferior vena cava.
• Sideways, through the internal iliac veins, which join the large veins coming up from the legs.

Like leg veins, the ovarian veins contain small one-way valves. These stop blood falling back down when you stand.

For an overview of the condition itself, see our guide to pelvic congestion syndrome.

Cause 1: Ovarian vein reflux

The most common cause is ovarian vein reflux, also called ovarian vein insufficiency or incompetence. The valves are missing, too few, or stretched so they no longer close. Blood then falls back down the vein into the pelvis.

Over time the pelvic veins stretch, twist and hold more blood. This is the “congestion” that causes the dull, heavy ache described in our guide to pelvic congestion syndrome symptoms.

Why the left side is affected more often

Left ovarian vein reflux is much more common than right-sided reflux. Reasons include:

• The left ovarian vein is longer, so it carries a taller column of blood.
• It joins the left kidney vein at a right angle, which is less efficient for drainage.
• Studies of veins suggest valves are more often absent on the left.

Reflux in both ovarian veins, and in the internal iliac veins, also happens. Doctors need to know which veins are involved before planning treatment.

What a dilated left ovarian vein means

Scan reports may mention a dilated left ovarian vein. This means the vein is wider than usual. It is a common finding in women with PCS, but it is also seen in women with no symptoms at all, especially after pregnancy. A wide vein is only important if it fits with your symptoms and other tests.

Cause 2: Pregnancy

Pregnancy is the single biggest risk factor. During pregnancy:

• The amount of blood in the body rises sharply.
• Pelvic veins can widen by up to about half to carry it.
• Pregnancy hormones relax vein walls.
• The growing womb presses on veins in the pelvis.

After birth, the veins usually shrink back, but not always. Valves that were stretched may stay leaky. The risk rises with each pregnancy, and PCS is unusual in women who have never been pregnant.

Cause 3: Oestrogen and other hormones

Oestrogen relaxes and widens veins. This helps explain why:

• PCS mainly affects women before menopause.
• Symptoms often flare around periods.
• Symptoms usually ease after menopause, when oestrogen levels fall.

Polycystic ovaries have also been linked to pelvic vein problems in some studies, though the reason is not fully understood.

Cause 4: A squeezed vein higher up

Sometimes the pelvic veins are not the original problem. Instead, a vein further up is narrowed, and blood backs up and finds a way out through the pelvis.

• Nutcracker syndrome. The left kidney vein is squeezed between two arteries. Blood from the kidney then escapes down the left ovarian vein into the pelvis. See nutcracker syndrome.
• May-Thurner syndrome. The left common iliac vein is pressed against the spine by an artery that crosses over it. Blood from the left leg and pelvis is diverted through pelvic veins. See May-Thurner syndrome.

This matters because closing pelvic veins alone may not help if a compressed vein is the main problem. Compression is also common in people without symptoms, so it has to be judged carefully.

Other contributing factors

Less common causes and contributors include:

• Previous blood clots in the pelvic or leg veins, which can damage valves or narrow veins
• Previous pelvic surgery
• A womb that is tilted or has dropped (prolapse), which may affect drainage
• Rare vein malformations present from birth

Is pelvic congestion syndrome hereditary?

There is no single “PCS gene”. But a tendency to weak vein walls and valves does run in families. Women whose mother or sister has varicose veins seem to be more likely to develop pelvic vein problems. Many women with PCS have no family history at all.

Why wide veins do not always cause pain

One puzzle is that many women have widened, refluxing pelvic veins on scans and feel no pain at all. Others with similar scans have a lot of pain. Nobody fully understands why.

Possible reasons include differences in how sensitive the nerves around the veins are, how much the veins fill when standing, and whether other conditions are adding to the pain. This is why doctors look at the whole picture. A scan result alone does not prove that your veins are the cause of your pain, and treating veins that are not causing symptoms is not recommended.

Who is most at risk?

Putting this together, PCS is most likely in women who:

• Are in their twenties to forties, before menopause
• Have had two or more pregnancies
• Have varicose veins in the legs, vulva or buttocks
• Have a family history of varicose veins

Men can have the same kind of reflux, which usually shows up as a varicocele around the testicle.

Why the cause matters for treatment

Knowing which veins are refluxing, and whether something is squeezing a vein higher up, guides treatment. Reflux is usually treated by closing the faulty veins from the inside. A compressed vein may need a different approach. Our guide to pelvic congestion syndrome treatment explains the options and the limits of the evidence.

A patient guide to PCS causes and risk factors from a Singapore vascular surgeon’s clinic covers similar ground.

When to see a doctor

See a doctor if you have a dull, heavy pelvic ache that has lasted for months, pain that is worse after standing or after sex, or varicose veins around the vulva or upper thighs. Other conditions can cause the same symptoms, so it is worth being checked properly. Our pelvic symptom check can help you prepare.

Get urgent medical help for sudden severe pelvic or abdominal pain, heavy vaginal bleeding, fever with pelvic pain, fainting, or a painful, swollen leg or sudden breathlessness. In Singapore, call 995 in an emergency.

This article is general information, not personal medical advice. Please speak to a doctor about your own symptoms. How we create our content.