Antiphospholipid Syndrome in Pregnancy

Antibodies are not the same as the syndrome

This is the distinction that causes most of the confusion, and it is worth getting straight before anything else. ACOG Practice Bulletin No. 132 defines antiphospholipid syndrome as "an autoimmune disorder defined by the presence of characteristic clinical features and specified levels of circulating antiphospholipid antibodies", and states that "diagnosis requires that at least one clinical and one laboratory criterion are met".

In plain terms, you need both: something that happened, and a blood test that stays positive. A single positive antibody found during a general screen, with no clinical event, is not antiphospholipid syndrome. Transiently positive results are common after infection, which is why the laboratory criteria require the test to be repeated and still positive at least 12 weeks later before the label is applied.

ACOG also notes in the same document that approximately 70% of people with APS are female, which is why the condition turns up so often in reproductive medicine. That is a figure about who has the syndrome, not about how likely you are to get it.

The three tests, and why all three are done

The laboratory criteria involve lupus anticoagulant, anticardiolipin antibodies and anti-beta-2 glycoprotein I antibodies. They are different assays measuring related things, and a person can be positive for one and negative for the others. Being positive for more than one, sometimes described as double or triple positivity, is generally treated as carrying more weight than a single low-level positive result.

ACOG is candid that this area is contested: the same Practice Bulletin observes there is "controversy about the indications for and types of antiphospholipid tests that should be performed in order to diagnose the condition", and that "much of the debate results from a lack of well-designed and controlled studies". If your results have been interpreted differently by two clinicians, that is why.

What counts as a clinical criterion in pregnancy

The obstetric criteria are specific and are the reason this condition is looked for at all. They cover three patterns: three or more unexplained consecutive miscarriages before 10 weeks, one or more unexplained deaths of a morphologically normal fetus at or beyond 10 weeks, and premature birth before 34 weeks caused by eclampsia, severe pre-eclampsia or recognised features of placental insufficiency. Vascular thrombosis, arterial or venous, is the non-obstetric clinical criterion.

RCOG's patient information on recurrent miscarriage puts the context around this: recurrent miscarriage, defined there as three or more early miscarriages, affects 1 in 100 (1%) women, and by far the most common single cause of miscarriage is chromosomal, accounting for 1 in 2 (50%) of them. APS is one of the treatable minority causes, which is exactly why it is worth testing for, and also why most recurrent miscarriage is not caused by it.

Treatment: named, not dosed

RCOG's recurrent miscarriage information states that if you have APS and have had recurrent miscarriages, "treatment with low-dose aspirin tablets and blood thinning injections (heparin) in pregnancy can increase your chance of having a successful pregnancy", because aspirin and heparin make your blood less likely to clot. This page names those treatments and gives no doses; the regimen depends on whether you have had a thrombosis, and that decision belongs to the team prescribing it.

RCOG draws a clear line between APS and inherited thrombophilias. On the latter, the same information says routine treatment for inherited thrombophilia "has not been found to improve your chance of a healthy pregnancy". Being told you carry factor V Leiden is not the same conversation as being told you have APS, and treating it as though it were leads to unnecessary injections.

What your pregnancy care looks like

Expect consultant-led care with extra surveillance aimed at the placenta, because that is where APS does its damage. In practice that usually means:

• early booking and a plan agreed in the first trimester rather than later
• blood pressure and urine checks at every contact, because APS raises pre-eclampsia risk
• serial growth scans, often with umbilical artery Doppler, because fetal growth restriction is the characteristic problem
• a documented thromboprophylaxis plan for pregnancy and, separately, for the six weeks after birth

RCOG's patient information on reducing the risk of venous thrombosis in pregnancy and after birth explains why the postnatal period is treated as a distinct risk window with its own plan. The after-birth part is the one most often left vague, so ask for it in writing before you go home.

Where APS and lupus overlap

APS can occur on its own or alongside systemic lupus erythematosus. The NHS antiphospholipid syndrome pages describe it as a condition in which the immune system produces antibodies that make blood more likely to clot, and note the association with other autoimmune conditions. If you have lupus as well, your care combines rheumatology and obstetric review, and telling an APS-related placental problem from a lupus flare or from pre-eclampsia becomes the central clinical question, which is another reason baseline blood and urine results in early pregnancy matter.

Birth planning

NICE guideline NG121, which covers intrapartum care for women with existing medical conditions, asks for the intrapartum plan to be made with a multidisciplinary team and agreed in advance rather than improvised in labour. For APS the practical questions are the timing of your last anticoagulant dose before birth, whether that affects your options for an epidural or spinal, and when anticoagulation restarts afterwards. Those three answers should be recorded in your notes well before you go into labour, because the anaesthetist who meets you at 3am will need them immediately.

What not to accept without a source

Live birth rates in treated APS are quoted very widely online and the numbers vary enormously depending on which population was studied, how APS was defined, and whether previous thrombosis was included. If you are given a percentage, ask which study it came from and who was in it. A figure without a denominator is not information.