When a woman with systemic lupus erythematosus learns she is expecting, one of her first questions is often whether she should stop her medicines. For hydroxychloroquine, the most widely used lupus drug, the evidence now gives a fairly clear answer. Across four decades of research, continuing it through pregnancy is associated with fewer lupus flares, and it has not shown a meaningful pattern of harm to the developing baby. It also appears to lower the risk of a rare but serious complication, congenital heart block, in babies of mothers who carry certain antibodies. This article sets out what the studies actually show, where the evidence is strong, where it is still developing, and what questions remain open. Two lives are at stake in every pregnancy, and good decisions start with an honest look at the evidence.

What hydroxychloroquine is and why it matters in lupus

Hydroxychloroquine belongs to a family of medicines with a long history. Its ancestor is quinine, taken from the bark of the South American cinchona tree and used against malaria for centuries. Chemists later developed chloroquine and then hydroxychloroquine, a close relative with fewer side effects. It is a fitting example of how remedies found in the natural world, studied with patience, have become tools for healing.

Hydroxychloroquine is approved in the United States for treating malaria, systemic lupus erythematosus and discoid lupus, and rheumatoid arthritis. It is not an immunosuppressant in the way chemotherapy-type drugs are. It works more as an immune modulator. Laboratory studies show it accumulates in the acidic compartments inside immune cells and interferes with signalling through receptors called toll-like receptors 7 and 9. These receptors help drive the overactive immune response in lupus. Outside pregnancy, long-term observational studies link hydroxychloroquine use with fewer flares, less organ damage and longer survival in lupus. That is why most rheumatologists regard it as a cornerstone treatment.

Flare prevention: the case for continuing

Pregnancy places real demands on a woman with lupus. Active disease in pregnancy is associated with higher rates of miscarriage, preeclampsia, preterm birth and poor fetal growth. Keeping the mother's disease quiet is one of the most effective ways to protect the baby.

The most-cited human evidence comes from two sources:

This is observational and modest-sized evidence, not a large definitive trial. But it is consistent and biologically plausible, and it fits with the broader non-pregnant data. One practical point is easy to overlook. Hydroxychloroquine has a very long half-life, so stopping it does not cause an immediate change. Its protective effect fades over weeks to months, which can happen to coincide with the middle of pregnancy.

Some studies have also suggested lower rates of preterm birth or preeclampsia among users. Those findings are inconsistent across cohorts, so they should be regarded as possible rather than established benefits.

Fetal safety: what the birth defect data show

Hydroxychloroquine crosses the placenta, so the question of fetal safety is reasonable. The reassuring evidence comes from several lines of research.

The most important recent study adds nuance. In 2021, Huybrechts and colleagues at Brigham and Women's Hospital and Harvard published an analysis in The BMJ of US Medicaid records. It included about 2,000 pregnancies exposed to hydroxychloroquine in the first trimester, compared with more than three million unexposed pregnancies. After adjusting for the underlying autoimmune disease and other factors, they found a small increase in major malformations. The adjusted relative risk was about 1.26. The signal appeared confined to daily doses of 400 mg or more, with a relative risk of about 1.33. Doses below 400 mg showed no increase. The study found no consistent pattern pointing to one particular type of birth defect.

The study's authors described the increase as small. In absolute terms it amounts to a few additional malformations per hundred exposed pregnancies at higher doses, and it is not certain the drug itself caused them. Other large datasets have not found a clear signal, and the finding has not yet been consistently replicated. The fair reading is this. Hydroxychloroquine is not proven to cause birth defects, a modest dose-related signal deserves attention, and that possible risk must be weighed against the documented risks of uncontrolled lupus. It also supports a careful conversation about dosing. Current practice generally keeps the dose at or below 5 mg per kilogram of actual body weight per day.

Concern about eye toxicity in exposed children, a theoretical worry because hydroxychloroquine can affect the adult retina with long-term use, has not been borne out in follow-up studies to date.

Congenital heart block: an emerging protective role

About a third to a half of women with lupus carry antibodies called anti-Ro/SSA, and some also carry anti-La/SSB. These antibodies can cross the placenta. In a small proportion of babies they damage the developing heart's electrical conduction system, usually between about 18 and 24 weeks. The result, complete congenital heart block, is permanent and serious. Many affected children need a pacemaker, and the condition carries meaningful rates of fetal and infant death.

For an anti-Ro-positive mother with no previously affected child, the risk is roughly 2 percent. After one affected child, the recurrence risk rises to somewhere in the range of 13 to 18 percent.

The evidence for hydroxychloroquine here has built step by step:

PATCH was open-label and single-arm, with no placebo group, and it was small. Its results are encouraging, and they match the earlier registry data. Still, they rest on comparison with historical rates rather than a randomised control group. Not every observational study has found a protective effect. Using hydroxychloroquine specifically to prevent congenital heart block is an off-label use that the FDA has not approved, even though the drug itself is approved for lupus. For many women with lupus the point is somewhat moot, because they would continue the drug for their own disease anyway.

What guidelines say, and the place of the informed patient

The American College of Rheumatology's 2020 Reproductive Health Guideline recommends continuing hydroxychloroquine during pregnancy in women with lupus. Where it is not already in use, the guideline also conditionally recommends starting it for all pregnant women with lupus. It suggests hydroxychloroquine for women with anti-Ro/SSA or anti-La/SSB antibodies, including those without lupus, because of its possible benefit against heart block. The European League Against Rheumatism (EULAR) has issued similar recommendations. Hydroxychloroquine is generally regarded as compatible with breastfeeding, since only small amounts pass into breast milk.

Guidelines summarise evidence, but the decision belongs to a woman and the physicians who know her. Several questions are worth bringing to that conversation:

Ideally, planning starts before conception. Lupus that has been quiet for at least six months before pregnancy is associated with better outcomes. Taking the medicine consistently also matters, because a drug cannot help if it is not being taken. Preparing in advance is a practical way for a mother to care for her child before the child is even born.

Key takeaway: The best available evidence indicates that continuing hydroxychloroquine through a lupus pregnancy helps keep the mother's disease controlled, has not shown a consistent pattern of harm to the baby at standard doses, and may lower the risk of congenital heart block in anti-Ro-positive mothers, so it is a decision worth making deliberately with one's own physician rather than stopping out of caution alone.