A quiet problem after a common infection
You're pregnant. You catch COVID. The cough clears. Life moves on.
But a few weeks later, your placenta — the organ feeding your baby — could be quietly struggling. And you might feel nothing at all.
That's the concern raised by a new Chinese study on pregnant women after SARS-CoV-2 infection.
COVID is still circulating. Most pregnant women who catch it recover without major problems.
But pregnancy changes how the immune system works. And the placenta depends on smooth blood flow through very small vessels. Anything that tips the body toward more clotting can cause trouble.
Antiphospholipid antibodies (antiphospholipid antibodies = immune proteins that can cause clots) are one such trigger. They are already known to cause miscarriage, preeclampsia, and placental problems in some patients.
The old view vs a new signal
Before COVID, antiphospholipid antibodies were mainly studied in people with autoimmune disease like lupus.
But here's the twist. Research during the pandemic showed that viral infections can sometimes kick the immune system into producing these same antibodies, at least temporarily.
This new study asked: how often does that happen in pregnant women, and does it affect the pregnancy?
How it works, in plain terms
Think of the placenta as a sponge full of tiny rivers.
Those rivers need to stay open for your baby to get oxygen and nutrients. Antiphospholipid antibodies are like small sticky clumps that can block the rivers. Fewer open rivers means less delivery.
Lupus anticoagulant (LAC) is one of the most important of these sticky clumps. Despite its name, it actually makes clotting more likely inside the body.
Researchers at Peking University People's Hospital ran a prospective observational cohort study.
They enrolled pregnant women who had a single (not twin) pregnancy, no pre-existing pregnancy complications, and who tested positive for SARS-CoV-2.
Between December 2022 and January 2023, they drew blood 2 to 4 weeks after each woman's COVID infection. They tested for three antibodies: LAC, anti-β2-glycoprotein I, and anticardiolipin. Then they followed outcomes through standard prenatal care.
Overall, about 1 in 5 infected pregnant women — roughly 19% — tested positive for at least one antiphospholipid antibody.
Every positive case showed just a single antibody. No one had multiple positives at the same time. That is actually reassuring: "triple-positive" patients are usually the highest risk.
The rate rose sharply with pregnancy stage. In the first trimester, fewer than 1 in 17 women tested positive. In the second, about 1 in 6. In the third, more than 1 in 4.
That third-trimester signal is the one to pay attention to.
Women who were positive, especially for LAC, had higher rates of placental-related complications. The authors identified LAC positivity as an independent risk factor for those outcomes.
Here's where it gets interesting
Most of these antibody findings may be temporary. Viral infections can cause short-lived "passenger" antibodies that fade.
But during pregnancy, even a temporary push toward clotting can matter. Timing is everything.
Obstetricians have watched carefully since the pandemic began for signs that COVID raises placental risk. This study adds specific, measurable data to those concerns.
The main takeaway fits broader experience: pregnancy plus a new viral infection deserves attentive follow-up, not panic. And later-pregnancy infections may need closer eyes than earlier ones.
If you are pregnant and have had COVID, share the timing with your obstetric team.
Based on this study, it may be reasonable to discuss antiphospholipid antibody testing 2 to 4 weeks after infection, especially if your infection was in the third trimester. Ask your provider.
Watch for signs of placental trouble: decreased fetal movement, sudden swelling, severe headaches, visual changes, or high blood pressure. Report them quickly. Standard prenatal monitoring becomes even more valuable in this setting.
This study does not suggest every pregnant woman with COVID develops complications. It identifies a subgroup that may benefit from extra attention.
This was a single-center study. The women were seen at one hospital in Beijing during a short time window.
The sample was enough to detect trends but not large enough to settle every question. We don't know how long these antibodies persisted or whether they stayed positive on repeat testing — a standard requirement for a true antiphospholipid syndrome diagnosis.
Different COVID variants may also trigger different immune responses, and this study came from a specific wave.
Larger multi-center studies are needed to confirm the numbers and see if routine post-COVID screening improves outcomes.
Trials could also explore whether any treatments — such as low-dose aspirin, already common in high-risk pregnancies — help women who test positive after a COVID infection. Until that evidence exists, care should be individualized with a trusted obstetric team.
