Maternal age can affect the chance of having twins, especially fraternal twins. As reproductive age advances, changes in ovarian function can make the development and release of more than one egg during the same cycle more likely. If two separate eggs are fertilized, a dizygotic, or fraternal, twin pregnancy can result.
This does not mean fertility increases with age. Overall fertility generally declines as ovarian reserve and egg quality decrease. It also does not mean that turning 35 suddenly changes your chance of twins. Age-related reproductive changes occur gradually, and observed twin birth rates are also influenced by fertility treatment, reproductive history, genetics, and other factors.
Quick takeaway:
- Advancing maternal age is associated more strongly with fraternal, or dizygotic, twins than with identical twins.
- The biological connection involves multiple follicular development and the possibility of releasing more than one egg in a cycle.
- Age 35 is a useful clinical threshold, not a biological switch.
- Overall fertility can decline even while the tendency toward multiple ovulation increases in some cycles.
- Population twin birth rates are not the same as an individual’s personal chance of naturally conceiving twins.
Chances of Twins by Maternal Age
Current U.S. birth data show a clear difference in observed twin birth rates across maternal age groups. According to the National Center for Health Statistics, the twin birth rate in 2024 increased from 16.1 twin births per 1,000 total births among mothers younger than 20 to 35.4 among mothers ages 35 to 39. The rate for mothers age 40 and older was 35.6 per 1,000 births.
| Maternal age | Twin births per 1,000 total births | How to interpret the group |
|---|---|---|
| Younger than 20 | 16.1 | Lowest observed age-specific rate in the CDC categories |
| 20-24 | 22.7 | Higher than the under-20 group |
| 25-29 | 28.9 | Observed twin birth rate continues to rise |
| 30-34 | 33.2 | Higher observed rate than in the 20s |
| 35-39 | 35.4 | Among the highest current age-specific rates |
| 40 and older | 35.6 | Very similar to the current rate for ages 35-39 |
Important: these figures are twin birth rates, not the probability that a person of a particular age will naturally conceive twins. The CDC defines the rate as the number of twin births per 1,000 total births. The data describe births that actually occurred in the U.S. population and therefore reflect many influences in addition to maternal age. These 2024 age-specific rates come from the U.S. National Center for Health Statistics’ June 2026 report on twin childbearing.
Source: CDC/NCHS, A Decade of Decline in Twin Childbearing in the United States, 2014-2024.
What These Numbers Actually Mean
Several different statistics are often described casually as the “chance of twins,” but they do not measure exactly the same thing.
- Twin birth rate: the number of twin births relative to all births in a population.
- Chance of a twin pregnancy: the probability that an established pregnancy involves twins.
- Natural twin conception probability: the likelihood of conceiving twins without fertility treatment.
- Individual probability: a person’s own likelihood after considering age together with other biological and treatment-related factors.
For that reason, a rate of 35.4 twin births per 1,000 births among mothers ages 35 to 39 should not be translated directly into a statement such as “a 37-year-old has a 3.54% natural chance of conceiving twins.” The population statistic and the individual biological probability have different denominators and include different influences.
Why Maternal Age Can Increase Fraternal Twinning
The strongest biological explanation for the maternal-age relationship involves the ovaries, ovarian follicles, and follicle-stimulating hormone, commonly abbreviated as FSH.
Each menstrual cycle involves hormonal signals that recruit ovarian follicles. A follicle is a fluid-filled structure in the ovary that contains a developing egg. Normally, one follicle becomes dominant and one egg is released at ovulation. In some cycles, however, more than one follicle develops far enough that multiple eggs may become available for ovulation.
Research examining spontaneous ovulatory cycles has found that multifollicular development becomes more common with advancing reproductive age. In one study of 959 spontaneous ovulatory cycles, women with more than one large developing follicle were, on average, older and had higher basal FSH concentrations than women with a single large follicle. This offers a biological explanation for why dizygotic twinning can become more common even while overall fertility is declining.
Research source: Human Reproduction study on maternal age, FSH and multifollicular development in 959 spontaneous ovulatory cycles.
FSH and Multiple Follicular Development
FSH is produced by the pituitary gland and helps stimulate the growth and development of ovarian follicles. As ovarian function changes with reproductive aging, the hormonal feedback between the ovaries and the brain also changes. In some women and some cycles, this can be associated with higher FSH stimulation and the development of more than one sufficiently mature follicle.
The important concept is not simply that “older women have more FSH.” Reproductive endocrinology is more complex than a single hormone value. The relevant pathway is that age-related changes in ovarian feedback can make multiple follicular development more likely in some ovulatory cycles.
How maternal age can influence fraternal twinning:
Reproductive aging → changes in ovarian hormonal feedback → multiple follicular development → more than one egg may be released → two eggs may be fertilized → possible fraternal twins
- FSH stimulates ovarian follicles.
- More than one follicle may develop sufficiently during the same cycle.
- More than one egg may be released at ovulation.
- If two eggs are each fertilized, two embryos can begin developing.
- This can result in fraternal, or dizygotic, twins.
Multiple follicles do not guarantee multiple ovulation, and multiple ovulation does not guarantee twins. The eggs still have to be fertilized, implant successfully, and continue developing.
Hyperovulation and the Release of More Than One Egg
Hyperovulation is a commonly used term for releasing more than one egg during the same ovulatory cycle. It is the biological event most directly relevant to spontaneous fraternal twinning.
If two eggs are released and only one is fertilized, there will not be a fraternal twin pregnancy. If both are fertilized but only one successfully implants or continues developing, the pregnancy may ultimately be a singleton. Maternal age therefore changes one part of the pathway rather than determining the final outcome.
Why Maternal Age Mainly Affects Fraternal Twins
The age relationship makes more sense when fraternal and identical twins are considered separately. They begin through different biological processes.
| Feature | Fraternal twins | Identical twins |
|---|---|---|
| Scientific term | Dizygotic twins | Monozygotic twins |
| Eggs involved | Two separate eggs | One egg |
| How they begin | Two eggs are fertilized separately | One fertilized egg later divides into two embryos |
| Connection with multiple ovulation | Direct | Not required |
| Relationship with maternal age | Clearer and stronger | Much weaker and less consistent |
Fraternal or Dizygotic Twins
Fraternal twins begin when two different eggs are fertilized by two different sperm. Because two eggs must be available, anything that makes multiple ovulation more likely can influence the chance of dizygotic twinning.
This is why maternal age, multiple follicular development, FSH, and hyperovulation belong to the same biological explanation.
Identical or Monozygotic Twins
Identical twins begin differently. A single egg is fertilized, and the resulting early embryo later separates into two developing embryos. Releasing two eggs is not required.
Epidemiological research has repeatedly found a much stronger maternal-age relationship for dizygotic twinning than for monozygotic twinning. Some studies describe monozygotic rates as relatively stable across much of the maternal-age range, while the rate of dizygotic twins changes much more noticeably with age.
For this reason, statements such as “older maternal age increases twins” are more accurate when interpreted primarily as an effect on fraternal twinning, rather than as an equal increase in every type of twin pregnancy.
Why Twin Chances Can Rise While Fertility Declines
At first, the relationship sounds contradictory. If fertility decreases with age, why would twins become more common?
The answer is that these statements describe different reproductive probabilities.
Ovarian Reserve and Egg Quality
A person’s supply of eggs is finite. With reproductive aging, ovarian reserve, meaning the remaining quantity of eggs, declines. Egg quality also declines with age, and conception can become more difficult.
These changes are major reasons overall fertility falls through the later reproductive years. Having an age-related tendency toward multifollicular development does not reverse this decline.
Multiple Follicles Are a Different Question From Overall Fertility
Consider two separate questions:
- How likely is pregnancy to occur at all?
- If ovulation occurs, how likely is more than one mature egg to be involved?
Advancing reproductive age can reduce the probability of successful conception overall while, in some ovulatory cycles, increasing the tendency for more than one follicle to develop. These processes can therefore move in different directions at the same time.
This is the key to the often-described paradox of declining fertility but increasing dizygotic twinning with advancing maternal age.
A greater tendency toward multiple ovulation does not mean a person becomes more fertile with age.
Is Age 35 Really a Turning Point?
No single birthday abruptly changes reproductive biology.
Age 35 has traditionally been used in obstetrics as the threshold for advanced maternal age, and it remains a useful clinical and research category. However, the threshold is a convention rather than an on-off biological boundary. Professional guidance acknowledges that many age-related risks and reproductive changes occur along a continuum and may become more pronounced at different ages.
The same principle applies to twins. A person does not suddenly start hyperovulating because they turn 35. Changes in ovarian reserve, hormonal feedback, follicular development, fertility, and pregnancy risk develop gradually.
So “35 and older” is useful shorthand when discussing population patterns, but it should not be interpreted as a precise biological cutoff for an individual’s chance of twins.
Clinical context: ACOG guidance on pregnancy at age 35 years or older treats maternal age as a continuum rather than an abrupt biological boundary.
What Changes Through Your 20s, 30s and 40s?
Maternal age is best understood as a gradual pattern rather than a series of fixed personal probabilities.
In Your 20s
Current U.S. data show lower observed twin birth rates in the 20s than in the 30s. The 2024 rate was 22.7 twin births per 1,000 total births at ages 20 to 24 and 28.9 at ages 25 to 29.
Natural twins can absolutely occur in the 20s. Maternal age is only one factor, and a younger age does not rule out either fraternal or identical twins.
In Your Early 30s
The observed twin birth rate rises further in the early 30s. For ages 30 to 34, the 2024 U.S. rate was 33.2 per 1,000 births.
At the biological level, reproductive aging and changes in follicular recruitment become increasingly relevant, although an age-group average cannot tell an individual whether multiple ovulation will occur.
Ages 35 to 39
The 2024 U.S. twin birth rate for mothers ages 35 to 39 was 35.4 per 1,000 births, among the highest of the age groups reported by the CDC.
This is also the age range in which the apparent fertility-twinning paradox becomes particularly important. Overall fertility is declining, yet research on spontaneous ovulatory cycles indicates that multifollicular development can be more frequent at older reproductive ages.
Age 40 and Older
For mothers age 40 and older, the U.S. twin birth rate was 35.6 per 1,000 births in 2024, almost identical to the 35.4 rate for ages 35 to 39.
This current pattern is important because it challenges the overly simple idea that twin rates must keep rising sharply with every additional year of maternal age. Historical studies of spontaneous dizygotic twinning have often found an increase through later reproductive age followed by a plateau or decline, depending on the population studied.
At the same time, overall natural fertility falls substantially in the 40s. A high population twin birth rate among people who give birth at these ages therefore should not be interpreted as evidence that becoming pregnant with twins naturally becomes progressively easier.
Natural Twin Chances vs Fertility-Treatment Twin Rates
Maternal age has a biological relationship with spontaneous fraternal twinning, but modern population statistics also reflect the use of fertility treatments. Keeping these pathways separate is essential when interpreting age-specific twin rates.
Natural or Spontaneous Conception
Without fertility treatment, the main age-related pathway is:
reproductive aging → altered ovarian hormonal feedback → greater likelihood of multifollicular development in some cycles → possible multiple ovulation → possibility of dizygotic twins
This describes a biological tendency, not a guarantee. Family history, reproductive history, population background, and other characteristics can also influence spontaneous dizygotic twinning.
ART, IVF and Fertility Medication
Assisted reproductive technology (ART) can create additional pathways to multiple pregnancy that are separate from the natural maternal-age mechanism.
- Medications used to induce or stimulate ovulation can result in the development and release of more than one egg.
- In vitro fertilization, or IVF, can produce a multiple pregnancy if more than one embryo is transferred and more than one implants.
- ART is also associated with an increased rate of monozygotic twinning compared with unassisted conception in some research.
Fertility-treatment practice has changed substantially over time. Professional reproductive-medicine guidance increasingly favors single-embryo transfer in appropriate patients to reduce multiple gestations. This has contributed to a large reduction in IVF-related multiple pregnancies compared with earlier treatment eras.
Clinical guidance: American Society for Reproductive Medicine guidance on multiple gestation associated with infertility therapy.
For that reason, an age-specific population twin birth rate represents a mixture of spontaneous biology, fertility-treatment exposure, treatment practices, and which pregnancies ultimately result in births. It is not a pure measure of the maternal-age effect.
Why Twin Birth Rates Have Changed Over Time
Twin birth statistics are not fixed.
The U.S. twin birth rate rose substantially for several decades, reaching 33.9 twin births per 1,000 total births in 2014. By 2024, it had declined to 30.1 per 1,000, an 11% decrease.
The changes were especially large among older maternal age groups:
| Maternal age | 2014 rate | 2024 rate | Change reported by CDC |
|---|---|---|---|
| 30-34 | 40.3 | 33.2 | 18% lower |
| 35-39 | 48.6 | 35.4 | 27% lower |
| 40 and older | 66.0 | 35.6 | 46% lower |
This is one reason older articles can give figures that look very different from current statistics.
Changes in assisted-reproduction practice are an important part of the wider context. For example, reproductive-medicine guidance has increasingly emphasized single-embryo transfer, and IVF twin rates have declined as single-embryo transfer has become more common. However, national twin-rate trends should not be attributed to one cause alone unless the data specifically support that conclusion.
For current population comparisons, the year and source of the statistic matter just as much as the number itself.
What Maternal Age Can and Cannot Predict
Maternal age is a meaningful population-level factor, but it is not a stand-alone prediction tool.
Maternal Age Can Help Explain
- why fraternal twinning rates differ between age groups;
- why multiple follicular development may become more common during later reproductive years;
- why population twin birth rates tend to be higher in older maternal age groups than in younger groups;
- why age should be considered alongside other factors when estimating twin likelihood.
Maternal Age Cannot Tell You
- whether two follicles will mature in a particular cycle;
- whether more than one egg will actually be released;
- whether both eggs will be fertilized;
- whether both embryos will implant and continue developing;
- whether an identical embryo split will occur;
- your complete individual chance of twins without considering other factors.
Age therefore works best as one input in a broader assessment rather than as a prediction by itself.
If You Are Already Pregnant With Twins, Does Maternal Age Add Risk?
The chance of conceiving twins and the risks of an existing twin pregnancy are separate questions.
Twin pregnancies have higher maternal and neonatal risks than singleton pregnancies overall, but research on how maternal age modifies those risks is more nuanced than a simple “older is always worse” rule.
A large U.S. population study examining twin pregnancies from 2007 through 2013 found that women ages 35 to 39 did not have higher adjusted risks of preterm birth than several younger groups, and advanced maternal age was not identified as an additional risk factor for fetal or neonatal death in that dataset. Preterm-birth risk did rise again among women in their 40s.
At very advanced maternal ages, additional concerns may become more important. A smaller retrospective study of twin pregnancies in women age 45 and older reported higher rates of hypertensive complications, preeclampsia, very low birth weight, neonatal intubation, and NICU admission compared with a younger comparison group.
These findings concern outcomes after a twin pregnancy already exists. They should not be used to calculate the probability of conceiving twins at age 40, 45, or any other age. Anyone who is pregnant with twins should receive individualized prenatal care based on age, medical history, chorionicity, pregnancy progress, and other clinical factors.
Other Factors That Affect the Chance of Twins
Maternal age is only one part of the overall picture. Other factors can influence twin likelihood, especially the probability of fraternal twins.
- Family history and genetics: inherited tendencies related to dizygotic twinning can matter, particularly through factors associated with multiple ovulation.
- Fertility treatment: ovulation-inducing medication, ovarian stimulation, IVF, and embryo-transfer practices can substantially change the probability of multiple pregnancy.
- Previous pregnancies and parity: reproductive history has been associated with twinning in population research, although its relationship with age and twin type is not identical in every population.
- Other population and biological factors: observed dizygotic twinning rates also differ across populations and can reflect additional genetic, reproductive, and environmental influences.
These factors should be considered together rather than using maternal age alone to estimate an individual’s likelihood of twins.
Frequently Asked Questions
At what maternal age are twins most common?
In current U.S. birth data, the highest age-specific twin birth rates are in the older age categories. In 2024, the rate was 35.4 per 1,000 births for mothers ages 35 to 39 and 35.6 for mothers age 40 and older. These are population birth rates, not personal natural-conception probabilities.
Can someone in their 20s naturally have twins?
Yes. Fraternal and identical twins both occur naturally in younger women. Maternal age changes probability at the population level; it is not a requirement for having twins.
Are fraternal twins more common after age 35?
Advancing maternal age is associated with a greater likelihood of dizygotic, or fraternal, twinning. The main biological explanation is that multiple follicular development and the release of more than one egg can become more common during later reproductive years.
Does maternal age increase the chance of identical twins?
The maternal-age association is much clearer for fraternal twins. Identical twins result from one fertilized egg dividing, so the multiple-ovulation mechanism does not apply. Research has generally found monozygotic twinning to vary much less with maternal age than dizygotic twinning.
Can maternal age alone predict whether I will have twins?
No. Age is one factor among several. Genetics, fertility treatment, reproductive history, twin type, and chance all matter. Age-specific birth statistics describe populations and cannot determine what will happen in an individual cycle or pregnancy.
Why do some older articles show much higher twin rates for women over 40?
Twin rates have changed over time. In U.S. data, the rate for mothers age 40 and older fell from 66.0 twin births per 1,000 total births in 2014 to 35.6 in 2024. Changing fertility-treatment practices are part of the context, and older statistics should not automatically be treated as current estimates.
Sources, Evidence and Methodology
This page separates three types of evidence that are often mixed together: current population birth statistics, research on the biology of spontaneous twinning, and studies of pregnancy outcomes after twins have already been conceived.
Priority was given to current government statistics, professional medical guidance, reproductive-medicine organizations, and peer-reviewed research. Population associations are not presented as guarantees for individuals, and treatment-related twin rates are distinguished from spontaneous conception wherever the distinction affects interpretation.
- National Center for Health Statistics: A Decade of Decline in Twin Childbearing in the United States, 2014-2024. June 2026. Source for current U.S. age-specific twin birth rates and national trend data.
- American College of Obstetricians and Gynecologists: Multiple Pregnancy. Clinical explanation of fraternal versus identical twins, multiple egg release, maternal age, and fertility-treatment effects.
- ACOG: Pregnancy at Age 35 Years or Older. Guidance on the conventional age-35 threshold and age-related pregnancy considerations.
- The paradox of declining fertility but increasing twinning rates with advancing maternal age. Human Reproduction. Study of 959 spontaneous ovulatory cycles examining maternal age, basal FSH, and multifollicular development.
- Maternal age and parity as predictors of human twinning. Research comparing maternal-age associations with dizygotic and monozygotic twinning.
- American Society for Reproductive Medicine: Multiple gestation associated with infertility therapy. Evidence and guidance concerning ovarian stimulation, ART, embryo transfer, and multiple pregnancy.
- Mayo Clinic: Pregnancy after 35. Patient-oriented guidance on fertility, egg quantity and quality, and interpretation of age 35.
- The Role of Maternal Age in Twin Pregnancy Outcomes. Population-based U.S. study separating maternal-age effects on outcomes after a twin pregnancy has been established.
- Twin pregnancy in women above the age of 45 years: maternal and neonatal outcomes. Study providing context for very advanced maternal age in established twin pregnancies.
Interpretation note: twin birth rates describe populations, not an individual’s exact chance of conceiving twins. Medical and fertility decisions should be discussed with a qualified healthcare professional who can consider personal reproductive history and clinical circumstances.