Find Information About:

Drugs & Supplements

Get information and reviews on prescription drugs, over-the-counter medications, vitamins, and supplements. Search by name or medical condition.

Pill Identifier

Pill Identifier

Having trouble identifying your pills?

Enter the shape, color, or imprint of your prescription or OTC drug. Our pill identification tool will display pictures that you can compare to your pill.

Get Started

My Medicine

Save your medicine, check interactions, sign up for FDA alerts, create family profiles and more.

Get Started

WebMD Health Experts and Community

Talk to health experts and other people like you in WebMD's Communities. It's a safe forum where you can create or participate in support groups and discussions about health topics that interest you.

  • Second Opinion

    Second Opinion

    Read expert perspectives on popular health topics.

  • Community


    Connect with people like you, and get expert guidance on living a healthy life.

Got a health question? Get answers provided by leading organizations, doctors, and experts.

Get Answers

Sign up to receive WebMD's award-winning content delivered to your inbox.

Sign Up

Health & Pregnancy

Font Size

Older Women More Likely to Have Twins

Fertility Treatments Aren't the Only Reason, New Study Shows
WebMD Health News
Reviewed by Louise Chang, MD

Feb. 22, 2006 -- As women age, their pregnancies are more likely to yield twins -- but why?

Fertility drugs and family history of twins are known to boost a woman's chances of having twins. Hormonal changes that come with age are another reason, a new study states.

The study comes from researchers at Vrije University Medical Centre in the Netherlands. They included professor Roy Homburg of the university's division of reproductive medicine.

Homburg and colleagues found that older women have higher levels of a hormone called FSH, prompting greater likelihood of having fraternal twins. The study appears online in Human Reproduction.

Hormone Shift

Data came from 507 women aged 24-41 who were undergoing intrauterine insemination due to unexplained infertility or mild male infertility. The researchers measured the women's hormones and checked ultrasound images of the women's reproductive system during a total of 959 cycles of ovulation.

Homburg's team compared women in their 20s with women in their 30s. Their findings:

  • Older women had higher levels of a hormone called FSH (follicle-stimulating hormone).
  • Older women were more likely to prepare more than one egg per menstrual cycle.

Those patterns were strongest in women aged 35 and older, followed by women aged 30-35, and lastly by women in their 20s.

Fraternal twins develop when two eggs are fertilized. So if older women are more likely to produce two eggs per cycle, they're also more likely to have fraternal twins, the researchers argue.

The study doesn't cover identical twins, which are much rarer and develop from one fertilized egg.

Birds, Bees, Hormones, and Age

Want a little more background?

During the follicular phase of a woman's cycle (which starts on the first day of her menstrual period), FSH and another hormone, called luteinizing hormone (LH), are released from the brain and travel through the blood to the ovaries. They stimulate about 15-20 eggs in the ovaries into individual "shells," called follicles.

Usually, only one of those follicles matures and is released during a woman's cycle. Think of follicles as a field of fledgling candidates, with only one getting the nod to go forward. Sometimes, more than one follicle gets released.

Pregnancy Week-By-Week Newsletter

Delivered right to your inbox, get pictures and facts on
what to expect each week of your pregnancy.

Today on WebMD

hand circling date on calendar
Track your most fertile days.
woman looking at ultrasound
Week-by-week pregnancy guide.
Pretty pregnant woman timing contaction pains
The signs to watch out for.
pregnant woman in hospital
Are there ways to do it naturally?
slideshow fetal development
pregnancy first trimester warning signs
What Causes Bipolar
Woman trying on dress in store
pregnant woman
Close up on eyes of baby breastfeeding
healthtool pregnancy calendar
eddleman prepare your body pregnancy