Do you ever wonder, as you agilely dodge around a doublewide stroller, if it really is becoming a Noah’s Ark world? Your perception is not wrong. The overall rate of twin births in the United States has grown by 76% over the last three decades. This increase in multiples is related to an increase in fertility treatments – and an increase in women in their thirties having babies. These both are independent, and not quite equal, risk factors for conceiving twins. Data tracking back to 1915 shows that the incidence of twins has always been highest for women ages 35-39, until 1997. From that point forward, the highest rate has been amongst women 40 and over. No doubt that transition was related to the increase in fertility treatments. In five of the fifteen states that mandate insurance coverage for fertility treatments, the twin rate rose over 100% for all age groups.  

Before we precede, here’s a brief primer on twins. Monozygotic or identical twins, occur when one egg and one sperm form a zygote that splits into two babies instead of remaining as one. This occurs in approximately 1 in 400 pregnancies. All women have an equal chance of conceiving them and that chance is not influenced by fertility treatments. Dizygotic or fraternal twins, occur when two eggs are fertilized by two separate sperm. Genetically speaking, they are no different than any other sibling set; they just happen to be wombmates. They have a tendency to run in families. This is because some women have a propensity to release more than one egg per month, and this unique skill may be genetic. Despite what you may have heard, twins do not skip a generation. Nor is there a need to worry if the twins run on your husband’s side, as that wouldn’t influence your ovaries’ behavior.

So what are your actual chances of having twins? Here’s where you get to relax. If you are not using any fertility treatments, then pretty low: around 3%. Oral fertility medications like Clomid or Letrozole can increase your chances to about 10%. Ironically, according to one fertility specialist, IVF gives you the best chance of not having twins because they can implant only one embryo (although they typically implant at least two). But as the saying goes: “We make plans and God laughs.”

Erin, age 38, and mother of 3 young boys shares her experience:

“All of my children are modern medical miracles. Going into the process, my husband and I always knew that getting pregnant could mean getting pregnant with multiples. In fact, during one IVF cycle, after retrieving five “good” eggs, we had a conversation with our fertility doctor in which he said he would implant all five embryos if they fertilized. Our mouths dropped – five children at once! But our doctor assured us that a pregnancy of multiples of that magnitude was rare; he wanted to increase our chances of conception with as many opportunities as possible. Thank goodness that round only resulted in one or two viable embryos, and ultimately the cycle was a failure. 

When we did conceive our first son, we implanted two embryos. So twins were a real possibility when we went in for our first ultrasound. Once we confirmed that the pregnancy resulted in a singleton, we tucked away our ‘what-if’ feelings of the embryo that didn’t take and moved on to prepare ourselves for this new little person who would be joining our family. Once our son was born, we both exhaled a sigh of relief, and weeks later said to each other ‘Thank God he wasn’t a twin!’ Nothing can prepare you for becoming a new parent, and babies are a lot of work. Of course, there is a lot of joy in that work, but neither one of us could imagine taking care of two little ones at the same time.  

Fast forward two years, when we decided to try to expand our family and give our older son a sibling. Again with this IVF cycle we implanted two embryos. When I received news that my blood test was positive for pregnancy, I was excited and looked forward to the first ultrasound to see the baby. As the technician started her scan she said she saw one gestational sac. I looked at my husband and smiled – that meant only one embryo took.  And then the technician said that she saw two yolk sacs. I looked at her with confusion and asked what that meant.  She replied that the embryo split and it looked like I was pregnant with identical twins. 

I was in complete disbelief and panicked a bit. My mind raced with thoughts like ‘How am I going to nurse two babies with an active two-and-a-half-year-old?’ or ‘I need to buy a minivan.  I hate minivans… but we are going to need one.’ or ‘I’m never going to be able to leave my house again.’ It took much of the pregnancy to wrap my mind around what our life was going to be like once the babies arrived. And even then, nothing prepares you for the arrival of two babies at once.

Adapting to life with twins is difficult, but not nearly as hard as I thought it would be. On a practical level, there are many more trips up and down stairs, the babies cry a lot more than my first son, and getting everyone together to leave the house takes at least thirty minutes. But we do leave the house. And we did not have to buy a minivan. And two charming, funny, inquisitive little boys are now a part of our lives, and we can’t imagine it any other way.”


Martin JA, Hamilton BE, Osterman JK, et al. Births: Final data for 2012. National vital statistics reports; vol 62 no 9. Hyattsville, MD: National Center for Health Statistics. 2013

Martin JA, Hamilton BE, Osterman MJK. Three decades of twin births in the United States, 1980–2009. NCHS data brief, no 80. Hyattsville, MD: National Center for Health Statistics. 2012.

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