Yes. In some cycles, a woman may release two eggs instead of one, meaning that two follicles reach maturity and ovulate. If both eggs are fertilized by different sperm, this results in a twin pregnancy, specifically fraternal twins (also known as dizygotic twins).
This double ovulation becomes more common with age. After 35, the natural acceleration of follicle loss leads to hormonal changes that can mildly stimulate the ovaries, increasing the likelihood of releasing more than one egg in a cycle.
How double ovulation happens
At the start of each cycle, several follicles (the small sacs in the ovaries that each contain an egg) begin to grow under the influence of follicle-stimulating hormone (FSH). Usually one becomes dominant and the others stop growing. Sometimes two keep maturing. They are then released around the same time, triggered by the same hormonal surge, from the same ovary or one from each.
This isn’t a second ovulation later in the cycle. Once you’ve ovulated, the hormones of the second half of the cycle prevent new follicles from maturing until your next period.
Fraternal and identical twins
Fraternal twins come from two eggs fertilized by two sperm. They can be a girl and a boy, and they are no more alike genetically than any other brothers and sisters.
Identical twins come from a single fertilized egg that splits in two early on. They have nothing to do with double ovulation, and age, family history or fertility treatment have little or no influence on them.
What makes it more likely
- Age: FSH levels rise naturally in the late thirties, which makes it more likely that two follicles mature.
- Family history: fraternal twins tend to run in families on the mother’s side, because the tendency to release two eggs can be inherited.
- Previous pregnancies: having already had fraternal twins, or several pregnancies, raises the likelihood.
- Origin: fraternal twins are notably more common in women of West and Central African descent, and less common in women of East Asian descent.
- Fertility treatment: see below.
Fertility treatments and multiple eggs
Medicines that induce ovulation, whether tablets or hormone injections, can make several follicles mature at once. That’s why these treatments are monitored with ultrasound scans, and why your doctor may advise against having sex in a cycle where too many follicles have developed. In IVF, a twin pregnancy usually comes from transferring more than one embryo, which is why a single embryo transfer is now generally preferred.
Can you tell if you’ve released two eggs?
Not on your own. Ovulation tests, temperature charts and cervical mucus show that you’re ovulating, not how many eggs. Only an ultrasound scan around ovulation can show two mature follicles, and most women only find out at a pregnancy scan. Releasing two eggs doesn’t mean you’ll have twins: often only one is fertilized, or neither.
Does this mean fertility goes up after 35?
No. Double ovulation becomes a little more common, but overall fertility declines with age, mainly because the number and quality of eggs decrease. The chance of conceiving in each cycle goes down, even if a pregnancy that does happen is slightly more likely to be twins.
When to see a doctor
- You’re pregnant with twins: a twin pregnancy carries more risks and needs closer follow-up.
- You’re taking medication to induce ovulation: it should be prescribed and monitored by a doctor.
- No pregnancy after 12 months of regular sex without contraception, or after 6 months if you’re 35 or older.
