There is no reliable way to guarantee conceiving twins without fertility drugs. The baseline rate of twin births is about 3.1% of all deliveries, and most of those involve fertility treatments. That said, several biological factors genuinely shift the odds of releasing two eggs in a single cycle, a process called hyperovulation. Understanding these factors can help you assess your own likelihood, even if none of them function as a switch you can flip.
Fraternal (non-identical) twins are the only type influenced by these factors. They occur when two separate eggs are released and fertilized. Identical twins, which happen when a single embryo splits, occur at roughly the same rate worldwide regardless of genetics, diet, or any other variable.
Why Some Women Release Two Eggs
Fraternal twinning starts with follicle-stimulating hormone (FSH). This hormone triggers your ovaries to develop egg-containing follicles each cycle. Normally, one follicle wins out and releases a single egg. But when FSH levels are higher than average, two follicles can mature simultaneously, each releasing an egg. Studies of mothers who conceived fraternal twins have consistently found elevated FSH levels compared to mothers of singletons.
FSH levels aren’t purely random. They’re influenced by your genetics, your age, and signals from within the ovary itself. Two key proteins produced by developing eggs help regulate how many follicles mature. Genetic variations that alter how ovarian cells respond to FSH can increase the chance that two eggs reach maturity instead of one. This is why twinning tends to run in families on the mother’s side.
Genetics: The Strongest Natural Factor
If your mother or maternal grandmother had fraternal twins, your odds are meaningfully higher. Researchers have identified specific gene variants that influence spontaneous twinning. One variant is linked to higher circulating FSH levels. Another affects how ovarian cells respond to that FSH, potentially increasing their sensitivity so that more follicles mature even at normal hormone levels.
These are maternal genes. The father’s genetics do not influence whether a woman releases one or two eggs. However, a man can carry twinning gene variants and pass them to his daughters, who may then have a higher chance of conceiving twins themselves. If fraternal twins appear on either side of your family, the trait may eventually express through a female relative.
Age: A Surprising Advantage After 35
Women over 35 are statistically more likely to conceive fraternal twins if they do become pregnant. The reason is straightforward: as women approach menopause, FSH levels rise as the body works harder to stimulate ovulation. That extra FSH can trigger the release of multiple eggs in a single cycle.
This creates an ironic situation. Fertility declines with age, making conception harder overall. But among women who do conceive naturally after 35, the probability of twins is higher than it was in their twenties. This is one reason the twin birth rate has climbed over the past few decades, as more women have children later in life.
Body Size: BMI and Height Both Matter
A large analysis of over 51,000 U.S. pregnancies (from before fertility drugs were widely used) found a clear relationship between body size and fraternal twinning. Women with a BMI of 30 or higher had significantly elevated odds of conceiving fraternal twins compared to women with a BMI under 20. The trend was consistent: as BMI increased, so did the twinning rate.
Height plays a role too. Women in the tallest quartile had a significantly increased odds ratio for fraternal twins, though the effect was smaller than for BMI. The likely mechanism involves insulin-like growth factor (IGF-1), a hormone that circulates at higher levels in taller and heavier individuals. IGF-1 increases ovarian sensitivity to FSH, which could promote the development of multiple follicles.
Dairy Consumption and IGF-1
The IGF-1 connection extends to diet. High milk consumption is associated with a 10% to 20% increase in circulating IGF-1 levels among adults. Not only do absolute levels rise, but the ratio of IGF-1 to its main binding protein also shifts, meaning more of the hormone is biologically active.
This has led some researchers to suggest that dairy-heavy diets could modestly increase twinning rates by boosting ovarian responsiveness. One frequently cited observation is that populations with high dairy intake tend to have higher fraternal twinning rates. However, the effect size in any individual woman would be small, and no controlled trial has tested whether increasing dairy intake actually raises someone’s chances of twins.
Folic Acid and Multivitamins
A Hungarian study tracking over 38,000 pregnancies found that women who took folic acid or multivitamins around the time of conception had slightly higher rates of twin pregnancies. Among women who took no supplements, the twin rate was 0.78%. For those who supplemented before conception, it rose to 1.52%. Combining folic acid with a multivitamin pushed the rate to 2.00%.
These are modest increases in absolute terms. The adjusted odds ratio for preconceptional supplementation was 1.80, meaning roughly an 80% increase in relative risk, but still a small overall probability. Folic acid is recommended for all women trying to conceive because it prevents neural tube defects, so this finding shouldn’t change your supplementation decisions. It’s simply an interesting association, not a twinning strategy.
Yams: Popular Claim, Weak Evidence
You’ll find many online sources claiming that eating yams, particularly wild yams, increases the chance of twins. The idea stems partly from the Yoruba people of Nigeria, who have one of the world’s highest natural twinning rates and eat a diet rich in yams. Lab studies have shown that Chinese yam extracts can increase estrogen and FSH levels in animal models, suggesting a possible hormonal effect.
But animal studies using concentrated extracts at specific doses don’t translate directly to eating yams at the dinner table. The active compounds in yam extracts are present at very low concentrations. No human study has demonstrated that eating yams increases ovulation rates or twinning probability. The Yoruba twinning rate is more likely explained by genetics than diet.
Previous Pregnancies
The relationship between number of previous births and twinning is more complicated than commonly stated. While twinning rates do increase with maternal age (which correlates with having had more births), recent analyses using large historical datasets found that the per-birth probability of twinning was not clearly associated with how many times a woman had given birth, once age was accounted for. In one Estonian dataset, twinning was most common among women’s final births, at 19.3 per thousand compared to 13.6 per thousand for earlier births. This may reflect biology, but it also reflects the fact that many women stop having children after twins, skewing the statistics.
What You Can Actually Influence
Most of the factors that increase twinning, including genetics, age, and height, are not things you can change. The modifiable factors (body weight, dairy intake, folic acid supplementation) have real but very small effects on an already low baseline probability. There is no natural method that brings your chances anywhere close to what fertility treatments achieve.
If you’re hoping for twins, the honest picture is this: a woman over 35 with a BMI over 30, a family history of fraternal twins, and a diet rich in dairy has the highest natural odds. But even with all those factors aligned, the vast majority of her pregnancies would still be singletons.
Risks Worth Knowing About
Twin pregnancies carry substantially higher risks than singleton pregnancies, which is worth weighing against the desire for multiples. Over 60% of twins are born premature, before 37 weeks. Premature babies often need intensive care for breathing, temperature regulation, and feeding. Women carrying twins are more than twice as likely to develop high blood pressure during pregnancy, more than twice as likely to become anemic, and face higher rates of cesarean delivery and postpartum bleeding. Twin babies have roughly double the risk of congenital abnormalities compared to singletons, including heart defects and neural tube problems.
None of this means twin pregnancies can’t go well. Many do. But the gap in complication rates between twin and singleton pregnancies is significant enough that it should factor into how actively you pursue this outcome.