No reliable evidence suggests that allergy shots cause miscarriage. Multiple studies spanning decades have compared pregnant women receiving allergen immunotherapy with those who were not, and the rates of miscarriage, preterm birth, congenital malformations, and other complications have consistently been similar or even slightly lower in the treatment groups. That said, the story is more nuanced than a flat “they’re safe,” because major allergy organizations still advise against starting allergy shots for the first time during pregnancy, even while agreeing that women already on a maintenance regimen can keep going.
What the Pregnancy Outcome Data Actually Show
The most reassuring evidence comes from studies that tracked real pregnancies in women receiving immunotherapy and compared them to controls. One of the earlier landmark studies followed 90 pregnancies in women getting allergy shots and found that the incidence of prematurity, toxemia, miscarriage, neonatal death, and congenital malformation was no greater than in the general population. Interestingly, a comparison group of 147 untreated pregnancies in allergic mothers had a higher rate of miscarriage than the treated group.1Journal of Allergy and Clinical Immunology. The safety of immunotherapy during pregnancy That finding has held up in more recent work. A review of studies covering both subcutaneous and sublingual immunotherapy found no significant difference in prematurity, high blood pressure or protein in the urine, congenital malformations, or perinatal deaths between women who continued allergy immunotherapy during pregnancy and controls.2PubMed Central. Allergen immunotherapy in pregnancy
A large Swedish registry study put hard numbers on the question by comparing pregnancies exposed to allergen immunotherapy against the broader population. The odds of congenital malformations, preterm birth, stillbirth, and cesarean delivery were all close to baseline, with none of the comparisons reaching a statistically meaningful difference.3The Journal of Allergy and Clinical Immunology: In Practice. Exposure to Allergen-Specific Immunotherapy in Pregnancy and Risk of Congenital Malformations and Other Adverse Pregnancy Outcomes These results held whether the shots were subcutaneous or sublingual, and they stayed consistent when researchers looked at subgroups like women with asthma, first-time mothers, and Swedish-born women specifically.
Among the few women in these studies who did experience generalized allergic reactions to their injections while pregnant, none were found to have fetal complications.4PubMed Central. Allergen immunotherapy in pregnancy That particular data point matters, because if allergy shots were going to threaten a pregnancy, you would expect the most dramatic reactions to be the ones that did it. The fact that even those pregnancies turned out fine is one of the stronger pieces of reassurance available.
Why Doctors Say “Don’t Start, But You Can Continue”
If the safety data are this encouraging, you might wonder why the World Allergy Organization and similar bodies still recommend against beginning immunotherapy during pregnancy. The guideline is clear: allergen immunotherapy should not be initiated in a pregnant woman, but a patient who was already on maintenance treatment before becoming pregnant can continue, as long as the allergen dose is not increased further.5PubMed Central. Allergic diseases and asthma in pregnancy, a secondary publication
The logic behind this split comes down to how allergy shots work in phases. During the buildup phase, when you are receiving gradually increasing doses to train your immune system, the risk of a systemic allergic reaction is higher. The maintenance phase, by contrast, keeps you at a stable dose you have already tolerated many times. The concern is not that the allergen itself harms the fetus. It is that a severe systemic reaction to a new or escalating dose could trigger a chain of events, including a dangerous drop in blood pressure, reduced blood flow to the uterus, and uterine contractions, that could jeopardize the pregnancy. Because the buildup phase carries a meaningfully higher chance of provoking that kind of reaction, guidelines recommend avoiding it in pregnancy even though the maintenance phase appears safe.6PubMed Central. Allergen immunotherapy in pregnancy
Some clinicians also slightly reduce the maintenance dose during pregnancy as an extra precaution, though the data do not clearly show this is necessary.7PubMed. Special Problems Regarding Allergen Immunotherapy The reduction is more of a conservative buffer than an evidence-based requirement.
Anaphylaxis and the Uterus
The theoretical danger to a pregnancy from allergy shots is not the allergen extract flowing through the bloodstream. It is anaphylaxis, the body’s most extreme allergic response. During anaphylaxis, blood pressure can plummet, oxygen levels drop, and the body releases chemicals that cause smooth muscle to contract. The uterus is smooth muscle. In severe cases, anaphylaxis from any trigger, not just allergy shots, could theoretically reduce blood flow to the placenta or provoke contractions strong enough to threaten a pregnancy.
A case series described four women who experienced what researchers called “uterine anaphylaxis” following subcutaneous allergy shots for environmental allergens. Symptoms included severe lower abdominal cramping that resembled menstrual cramps, along with hives, swelling, and flushing. None of these patients experienced uterine bleeding.8PubMed Central. Uterine Anaphylaxis Due to Subcutaneous Immunotherapy (SCIT) for Inhalant Allergens: A Case Series These cases were not in pregnant women, but they illustrate the mechanism that makes allergists cautious. If the uterus can contract forcefully during anaphylaxis, a pregnant uterus could respond similarly, at least in theory.
In practice, anaphylaxis from allergy shots is uncommon, and anaphylaxis severe enough to endanger a pregnancy is rarer still. The data from the pregnancy studies reviewed above found no fetal complications even among the women who had generalized reactions. But it is exactly this kind of low-probability-but-high-consequence scenario that drives the conservative stance on not beginning shots during pregnancy.
Venom Immunotherapy During Pregnancy
Allergy shots for bee and wasp stings, known as venom immunotherapy, present a distinct calculation. A woman allergic to insect stings faces a real risk of encountering a sting during a nine-month pregnancy, and an anaphylactic reaction to a sting is typically more severe than a reaction to an allergy shot. One estimate puts the risk of sting anaphylaxis in any untreated insect-allergic pregnant woman at roughly three to five percent per pregnancy.9Journal of Allergy and Clinical Immunology. Venom immunotherapy in the Hymenoptera-allergic pregnant patient That is not trivial when the consequence is anaphylaxis in someone carrying a baby.
Data from 26 women across 43 pregnancies while receiving venom immunotherapy showed that 36 pregnancies ended normally. Two women had mild reactions to their injections, neither of which required treatment. One child was born with multiple congenital abnormalities of unknown cause, but given that congenital malformations occur in roughly one of every 40 live births in the general population, that single case did not suggest an increased risk from the treatment.10Journal of Allergy and Clinical Immunology. Venom immunotherapy in the Hymenoptera-allergic pregnant patient A more recent review likewise concluded that venom immunotherapy is safe for pregnant women and their infants, and that for women with a history of severe sting reactions, stopping treatment may actually be riskier than continuing it.11PubMed Central. Venom immunotherapy and pregnancy
The takeaway for venom-allergic women is that the calculation tilts more strongly toward continuing treatment, because the alternative, walking around unprotected from a sting that could trigger full-blown anaphylaxis, carries its own serious risks to the pregnancy.
Sublingual Immunotherapy as an Alternative Route
Sublingual immunotherapy, where the allergen is placed under the tongue as drops or a dissolving tablet rather than injected, carries a lower risk of systemic reactions than subcutaneous shots. That makes it an interesting option for pregnant women, at least in theory. A prospective study following women who received sublingual immunotherapy during pregnancy found that over six years of follow-up, the incidence of pregnancy complications was actually lower than in the general population, and higher in both control groups that were not on treatment.12PubMed. A prospective study on the safety of sublingual immunotherapy in pregnancy
The same general guideline applies, though: sublingual immunotherapy should ideally be started before pregnancy, not during it. The Swedish registry study mentioned earlier found that the safety profile looked similar whether the immunotherapy was subcutaneous or sublingual.13The Journal of Allergy and Clinical Immunology: In Practice. Exposure to Allergen-Specific Immunotherapy in Pregnancy and Risk of Congenital Malformations and Other Adverse Pregnancy Outcomes So the sublingual route is not a workaround that lets you safely begin immunotherapy during pregnancy, but it does offer the advantage of milder systemic reactions overall, which adds a layer of comfort for women continuing treatment.
What to Do If You Get Pregnant While on Allergy Shots
This is one of the most common real-world scenarios, and it often catches people off guard. You have been getting allergy shots for months or years, and you discover you are pregnant. Should you stop immediately? The evidence says no, not if you are already on a stable maintenance dose and tolerating it well. Abruptly stopping immunotherapy can lead to a loss of the immune tolerance you have been building, meaning your allergy symptoms may return or worsen during a pregnancy when you already have fewer medication options. The practical advice from guidelines is to continue at your current dose, avoid any increases, and keep your allergist and obstetrician informed.
If you are still in the buildup phase when you become pregnant, the decision is less straightforward. Some allergists will pause the dose escalation and hold you at whatever dose you last tolerated without trouble. Others may recommend stopping entirely until after delivery and then restarting. There is no strong data to say one approach is clearly better, but the principle remains the same: the risk that concerns everyone is a systemic reaction from a dose your body has not yet proven it can handle.
You should also make sure the clinic where you receive your shots knows you are pregnant. Standard protocol already requires a waiting period after each injection, typically about 30 minutes, so that any reaction can be treated on site. That waiting period is even more important during pregnancy because treating a reaction quickly means the fetus is exposed to less physiological stress.
Uncontrolled Allergies and Asthma May Be the Bigger Threat
Much of the worry about allergy shots during pregnancy focuses on what the treatment might do, while overlooking what happens when allergies and asthma go untreated. Poorly controlled asthma during pregnancy is associated with preeclampsia, preterm birth, and low birth weight. Severe nasal congestion and chronic inflammation can disrupt sleep and reduce oxygen delivery. If allergy shots are the reason your asthma is well controlled, stopping them abruptly could leave you worse off than continuing.
This is the trade-off allergists are actually weighing when they counsel pregnant patients. It is not just whether the shots carry risk in isolation. It is whether continuing them produces a better outcome than the alternative of worsening symptoms managed with fewer medication options. For many women, continuing maintenance immunotherapy is the least risky path available.
Could Allergy Shots During Pregnancy Affect the Baby’s Allergy Risk?
One of the more intriguing threads in this area is the possibility that allergen immunotherapy during pregnancy might actually reduce the chances that the baby develops allergies later in life. Immunotherapy shifts the mother’s immune response in ways that dampen allergic inflammation, and there is some preliminary evidence suggesting those immune changes can cross the placenta and influence the developing fetal immune system.14PubMed. Should we encourage allergen immunotherapy during pregnancy?
This is far from settled science. The studies are small and observational, and no randomized trial has tested whether giving immunotherapy to pregnant women protects their children from developing allergies. But the idea is biologically plausible and has attracted enough interest that some researchers have openly asked whether we should be encouraging, rather than merely tolerating, immunotherapy during pregnancy. For now, it remains a research question rather than a clinical recommendation, but it adds context to the broader picture: there are potential upsides to continuing treatment, not just an absence of harm.
Myths and Misunderstandings Worth Clearing Up
Several persistent misconceptions circulate online about allergy shots and pregnancy, and they tend to create unnecessary anxiety.
- The allergen itself harms the baby: The extracts used in allergy shots are tiny quantities of proteins, things like dust mite fragments or grass pollen. They do not cross the placenta in any meaningful amount, and there is no evidence they are toxic to a developing fetus. The concern has always been about the mother’s reaction to the injection, not the injection contents reaching the baby.
- Any reaction means the pregnancy is in danger: Local reactions at the injection site, like redness, swelling, and itching, are common and carry no risk to a pregnancy. Even mild systemic reactions like hives or a runny nose are not associated with fetal complications. The specific concern is severe anaphylaxis with a dangerous drop in blood pressure, which is rare.
- You need to wait until after breastfeeding to restart: There is no medical reason to delay restarting immunotherapy until you are done breastfeeding. The allergen extracts are proteins that would be digested if they reached breast milk at all, and guidelines do not restrict immunotherapy during lactation.
- Sublingual drops are inherently safer than shots during pregnancy: The systemic reaction rate is lower with sublingual immunotherapy, which is a genuine advantage, but the pregnancy outcome data look similar for both routes. Sublingual is not a magic bullet that eliminates concern, just a lower-risk profile for one specific complication.
Omalizumab and Other Biologic Therapies
Some women with severe allergic conditions are on biologic medications like omalizumab rather than, or in addition to, traditional allergy shots. The safety data for biologics during pregnancy are thinner than for allergen immunotherapy, but a systematic review of omalizumab use during pregnancy looked at 67 women and found only one miscarriage reported among them.15PubMed Central. Effectiveness and Safety of Omalizumab for Chronic Spontaneous Urticaria During Pregnancy: A Systematic Review That is a small sample, so it would be premature to call omalizumab definitively safe in pregnancy, but the early signal is not alarming. Around 28 of the 67 women chose to stop omalizumab as soon as they learned they were pregnant, while others continued, reflecting how unsettled the guidance remains for this class of treatment. Biologics are a different conversation from traditional allergy shots, but they come up frequently enough in the same clinical discussions that they are worth mentioning. If you are on a biologic for allergies and become pregnant, the decision to continue or stop should be individualized with your allergist and obstetrician rather than driven by blanket rules.