The weight of current evidence says no, your ABO blood type does not have a meaningful effect on your ability to get pregnant. Multiple studies and a major meta-analysis have found no link between being type A, B, AB, or O and measures of fertility like ovarian reserve or natural conception rates. Where blood type does matter during reproduction is a different story: the Rh factor can cause serious complications during pregnancy if there is a mismatch between a mother and her baby, and a few studies hint at loose associations between certain blood types and conditions like endometriosis. But the idea that your letter on a blood-type card predicts how easily you will conceive is not supported by the research.
The Ovarian Reserve Question
Much of the interest in blood type and fertility traces back to a 2011 study from the Albert Einstein College of Medicine that suggested women with type O blood were more likely to have diminished ovarian reserve. That finding generated headlines and anxiety, but subsequent research has not backed it up. A systematic review and meta-analysis pooling data from multiple studies found no relationship between ABO blood type and ovarian reserve, whether measured by follicle-stimulating hormone (FSH) or anti-Müllerian hormone (AMH), the two standard markers clinicians use to estimate how many eggs a woman has left.1PubMed Central. ABO blood group and ovarian reserve: a meta-analysis and systematic review None of the individual blood types showed a statistically significant difference from any other.
A separate study that specifically set out to test this question reached the same conclusion: after adjusting for age, neither ABO group nor Rh factor was associated with ovarian reserve. The only factor that predicted lower reserve was age itself.2PubMed Central. Only Female Age, and Not Blood Type, Is Associated with Ovarian Reserve A third study looked at ovarian reserve from the practical angle of IVF egg retrieval and found no significant differences in the number of mature eggs collected, fertilization rates, or pregnancy and birth rates across blood types.3PubMed Central. Implications of Blood Type for Ovarian Reserve and Infertility – Impact on Oocyte Yield in IVF Patients And a large analysis published in Fertility and Sterility concluded directly that blood type O is not associated with diminished ovarian reserve, and that there are no clinical grounds for using blood type as a risk factor for low egg supply.4PubMed. Association of blood type and patient characteristics with ovarian reserve
This is one of those cases where an early, widely publicized finding did not hold up when more researchers tried to replicate it. If you have been told your blood type puts you at risk for low ovarian reserve, the current consensus is that it does not.
What IVF Studies Show About Blood Type and Live Birth
Because IVF clinics collect detailed data on every patient and cycle, they offer a useful lens for studying whether blood type influences reproductive outcomes. The results here are mostly reassuring, with one exception that is hard to interpret.
A study of single-embryo transfer cycles found no significant difference in live-birth rates when comparing blood types A, B, AB, and O. There was also no difference in birth weight or gestational age at delivery.5PubMed. Association between ABO blood type and live-birth outcomes in single-embryo transfer cycles Another analysis comparing women with type O to those with non-O types found no statistically significant differences in live birth, positive pregnancy test, clinical pregnancy, or miscarriage rates.6PubMed Central. Non-O blood group and outcomes of in vitro fertilization And a study looking at whether follicular fluid cytokine profiles vary by blood type found no correlation between ABO group and embryo quality or pregnancy test results in IVF patients.7PubMed. Blood type ABO and the cytokine profile of follicular fluid in women undergoing IVF/ET
The outlier is a study that found women with type B blood had roughly double the odds of a live birth after IVF compared to other blood types, even after adjusting for the usual factors that influence cycle success.8PubMed Central. Blood type predicts live birth in the infertile population That is a striking finding, but it stands alone. The studies cited above, which are larger or more recent, did not replicate it. In fertility research, isolated positive findings from single centers are common and frequently do not survive replication. This one fits that pattern.
When Parental Blood Types Are Combined
A related question is whether the combination of both partners’ blood types matters. A large Chinese study examined how different pairings of maternal and paternal ABO types affected embryo development in IVF. Most combinations showed no effect on fertilization, cleavage, or high-quality embryo rates. The researchers did find a slight negative association between a female type B and male type A pairing and fertilization rate, but the effect was very small and the clinical significance questionable.9PubMed Central. Parent Joint AB Blood Group Is Associated With Clinical Outcomes of in vitro Fertilization and Intracytoplasmic Sperm Injection Treatment in Chinese Women
Earlier research from the 1970s investigated whether ABO incompatibility between spouses could cause “cervical hostility,” a condition where sperm struggle to move through cervical mucus. After studying over 50 couples with persistent, unexplained cervical-mucus incompatibility, the researchers concluded it was “highly unlikely” that blood group incompatibility contributed significantly to the problem.10PubMed. Blood group incompatibility and cervical hostility in relation to sterility The idea that mismatched partner blood types reduce your chances of conceiving naturally has never gained solid scientific footing.
The Rh Factor Is the Real Concern
While your ABO letter does not appear to matter much for fertility, the plus or minus sign next to it can. The Rh factor, specifically whether you are Rh-negative or Rh-positive, has well-established consequences for pregnancy, though less for conceiving in the first place and more for what happens afterward.
When an Rh-negative woman carries an Rh-positive baby (which happens when the father is Rh-positive), her immune system can develop antibodies against the baby’s red blood cells. This does not usually cause problems in a first pregnancy, but in subsequent pregnancies those antibodies can cross the placenta and attack the fetal blood cells, leading to hemolytic disease of the fetus and newborn. A study comparing pregnancy outcomes in Rh-negative versus Rh-positive women found significantly higher rates of neonatal jaundice, low birth weight, and intensive-care admissions in the Rh-negative group.11PubMed Central. Analysis of pregnancy and neonatal outcomes in 100 pregnant women with Rh-negative blood type
This is why Rh-negative pregnant women receive injections of Rh immunoglobulin (RhIg, commonly known by the brand name RhoGAM) during pregnancy and after delivery. The treatment prevents the mother’s immune system from forming antibodies in the first place, and it has dramatically reduced the incidence of severe hemolytic disease since it became standard practice in the late 1960s. If you are Rh-negative, this is genuinely important for your prenatal care, but it is a manageable medical situation rather than a barrier to having children.
Beyond the well-known Rh(D) system, rarer blood group antigens from systems like Kell, Duffy, and Kidd can also cause hemolytic disease. These account for a small fraction of cases, roughly three to five percent, but they are harder to catch because routine screening does not always test for them.12Intractable & Rare Diseases Research. Minor blood group incompatibility due to blood groups other than Rh(D) leading to hemolytic disease of fetus and newborn: a need for routine antibody screening during pregnancy Expanded antibody screening during pregnancy could catch these cases earlier.
Blood Type and Endometriosis
Endometriosis is one of the most common causes of fertility problems, affecting roughly one in ten women of reproductive age. A few studies have explored whether blood type plays any role in who develops it, and the results are interesting, if not conclusive.
A study of over 600 women in France found that while ABO group distribution was similar between women with endometriosis and controls, Rh-negative women were significantly more likely to have the disease. After adjusting for age, pain, BMI, and other factors, Rh-negative women had roughly twice the odds of endometriosis compared to Rh-positive women.13PubMed Central. ABO and Rhesus Blood Groups and Risk of Endometriosis in a French Caucasian Population of 633 Patients Living in the Same Geographic Area A separate, earlier study found a different pattern: blood group A was significantly overrepresented among women with endometriosis, with women carrying type A having nearly three times the odds of the condition, while type O was less common in endometriosis patients.14PubMed. ABO and Rh blood groups distribution in patients with endometriosis
These two studies point in somewhat different directions, which is not unusual in early research on a question like this. The Rh finding from the French study is intriguing because there is a plausible biological connection: Rh-negative individuals have subtle differences in immune regulation that could, in theory, influence the inflammatory environment that drives endometriosis. But these are associations found in relatively small populations, and nobody is suggesting women should worry about endometriosis based on their blood type alone. The condition’s causes are complex and still not fully understood.
Polycystic Ovary Syndrome and Blood Type
Polycystic ovary syndrome (PCOS) is another leading cause of infertility, and researchers have asked whether blood type predisposes women to it. The evidence here is contradictory. A study published in Medicine that compared ABO and Rh distributions between women with PCOS and healthy controls found the distributions to be essentially identical, concluding that blood type is not a risk factor for PCOS.15PubMed Central. Are ABO/Rh blood groups A risk factor for polycystic ovary syndrome?
A smaller study from Libya reported the opposite: it found that women with blood group O-positive were more likely to have PCOS and showed the expected hormonal abnormalities of low FSH and elevated LH levels.16Journal of Libyan Academy Bani Walid. A study of hormonal changes and genetic frequency of ABO blood groups and Rh factor (RH) in women with polycystic ovary syndrome in Sebha city When two studies flatly contradict each other, the research is simply too early-stage to draw conclusions. The causes of PCOS involve insulin resistance, androgen levels, and complex genetic and environmental factors. Blood type, if it plays any role at all, would be a very minor player.
Blood Type, Miscarriage, and Pregnancy Complications
The question of whether ABO incompatibility between mother and fetus contributes to miscarriage has been debated for decades. Some older reports suggested that incompatible matings (for example, a type O mother carrying a type A fetus) might lead to higher rates of spontaneous abortion. But as a review of the literature noted, the effects seen in some studies were not observed in others, leaving the picture unresolved.17PubMed Central. The Incidence of Spontaneous Abortion in Mothers with Blood Group O Compared with other Blood Types The IVF data cited earlier, showing no difference in miscarriage rates between type O and non-O women, further weakens this theory.
A different pregnancy complication, preeclampsia, has shown a more consistent link with blood type. A systematic review and meta-analysis found an association between the AB blood group and preeclampsia.18PubMed. Preeclampsia and ABO blood groups: a systematic review and meta-analysis The proposed mechanism involves ABO blood groups’ known influence on blood clotting and blood vessel function. People with non-O blood types tend to have higher levels of von Willebrand factor and factor VIII, both of which promote clotting, and preeclampsia involves abnormal blood vessel behavior in the placenta. Type AB, which carries both A and B antigens, may be on the far end of this spectrum. That said, the meta-analysis was based on only two original studies, so the finding needs more replication before it should change how anyone manages their pregnancy.
Secretor Status and the Vaginal Microbiome
Your blood type genetics influence more than just the antigens on your red blood cells. A related gene called FUT2 determines whether you are a “secretor,” meaning you express blood group antigens in your saliva, mucus, and other bodily fluids. About 20 percent of people of European descent are non-secretors, meaning their FUT2 gene is nonfunctional. This distinction affects which bacteria can colonize your mucosal surfaces, including the vagina.
Research has found that mutations in FUT2 that knock out secretor status may shape the vaginal microbiome in ways that affect birth outcomes, specifically preterm birth risk.19PubMed Central. Secretor status is a modifier of vaginal microbiota-associated preterm birth risk The vaginal microbiome plays a well-established role in reproductive health: a community dominated by certain Lactobacillus species is generally protective, while a more diverse, less stable community is associated with bacterial vaginosis, which in turn raises risks for preterm birth and can impair fertility. If your secretor status alters which bacteria thrive in your reproductive tract, it could be an indirect pathway through which blood-type genetics influence reproductive outcomes, even if the ABO letter itself does not.
This is an area where the science is genuinely young. Secretor status is rarely tested outside of research settings, and there are no clinical recommendations tied to it yet. But it illustrates a broader point: the genes near or within the ABO region on chromosome 9 do many things beyond determining what sticker goes on your blood bag. Future research that accounts for these related genetic variants might find subtler connections that ABO-only studies miss.
What About Male Fertility
Most of the research on blood type and fertility has focused on women. Studies involving men are fewer and less conclusive. One investigation of over 1,500 men looked at the distribution of blood types among fertile men versus those being treated for infertility, but the findings were limited to observing that the ratio of infertile patients to fertile controls was about three to one in their clinic population, without establishing a clear causal link between any specific blood type and sperm quality or count.20PubMed Central. Relationship between blood groups and male infertility
Male fertility is primarily influenced by factors like sperm count, motility, and morphology, which are in turn affected by genetics (but not blood-type genetics as far as current evidence shows), lifestyle, age, and environmental exposures. If you are a man wondering whether your blood type matters for fertility, the honest answer is that nobody has found a convincing reason to think it does.
Why This Myth Keeps Circulating
Blood type has a peculiar status in popular health culture. Entire diet plans have been built around it. In some countries, particularly Japan and South Korea, blood type is treated as a personality indicator in much the way Westerners use astrology signs. Against this backdrop, the idea that blood type might predict fertility fits neatly into an existing narrative that your A, B, AB, or O classification reveals deep truths about your biology.
The scientific reality is less dramatic. ABO blood type determines which sugar molecules sit on the surface of your red blood cells, and this has well-documented consequences for transfusion compatibility, organ transplantation, and certain disease risks (type O, for instance, is associated with lower risk of heart disease but higher susceptibility to cholera). But fertility is governed by an enormous web of hormonal, genetic, anatomical, and environmental factors, and the ABO system does not appear to be a significant thread in that web. The Rh system matters for pregnancy management, and secretor status may influence the vaginal microbiome in ways that touch reproductive health. Beyond those specific mechanisms, the research consistently comes back to the same answer: your blood type letter is not something your fertility doctor needs to worry about when helping you conceive.