How Often Are Twins Discovered Late in Pregnanc?

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Author Name: Mia Barnes
Date: Thursday September 20, 2018

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When you’ve just found out that you’re becoming a mother, you’re quickly thrown into one of the most exciting and exhilarating times of your life. There’s the rush of joy that’s followed by the concern to learn everything you can in order to ensure a smooth pregnancy. Going to your doctor regularly is a big part of that, since they’ll be able to help you weed out fiction and decipher fact in what you read in books or online.

Another part of being pregnant is hearing everyone in your life tell you the craziest pregnancy stories that they’ve heard. Most will turn out to be myths, but you may double check them all anyway just to be sure. If you’ve heard about twins being discovered late in a pregnancy, it’s one of the powerful stories that can get stuck in your mind throughout every trimester.

It’s hard enough planning for one baby without worrying about whether there will be more. Even if you’re told multiple times by your doctor that you’re only having one, you might still be convinced you’re having double. Tales of twins discovered late in pregnancy may cause you to wonder, how often are twins missed on ultrasounds, really? Is there any way to be extra sure that what you’re seeing on your ultrasound is the truth?

The thought of overlooking an entire baby on an ultrasound is worrisome. You want to be as prepared as possible for however many babies you have before they arrive. The last thing any mother wants is to bring a baby home to a place where they don’t have what they need. But before you go buying a second crib, take a moment to read what experts have to say about the likelihood — or unlikelihood — of twins discovered late in pregnancy.

How Often Are Twins Missed on Ultrasounds?


An ultrasound is the best way to get information about your pregnancy. It allows you and your doctors to see clearly inside the womb from multiple angles. Without ultrasounds, it’d be much more difficult for doctors to figure out the most basic information, like whether your baby is developing at a normal pace and whether there are any reasons to be concerned. As ultrasound technology has increased, the more reliable the imaging has become. And today, it’s pretty dang reliable.

With very rare exceptions, your doctor should be able to detect twins via ultrasound by week ten at the latest. The later in the pregnancy the ultrasound is taken, the more obvious the twins will become. This is why sometimes you’ll find twins discovered late in pregnancy — although “late” is relative and usually refers to a difference of a few weeks. While the delay may be inconvenient if you’re hoping to get an early jump on baby prepping, you can rest assured that, if you have ultrasounds throughout your pregnancy, it’s highly unlikely you’re going to end up with twins discovered late in pregnancy.

Exceptions with Twins Discovered Late in Pregnancy?


While modern ultrasounds are overwhelmingly reliable, images from early-on in the pregnancy may not be able to rule out the possibility of twins conclusively. In ultrasounds taken in the first two months of pregnancy, one baby may conceal a secret sibling. This occurs when one twin is positioned directly in front of the other, blocking the second twin from view. This positioning happens most often with twins sharing the same amniotic sac, as they are forced closer together. However, even this is exceedingly rare. However, even this situation is exceedingly rare, as the twins would have to position themselves just right in order to fool the doctor, who would be using the ultrasound machine from different angles.

So how often are twins missed on an ultrasound? Although the likelihood is there, doctors will eventually notice the second baby. Even if they’re unable to detect the twin in the ultrasound, they will likely hear a second heartbeat or see other symptoms in the mother, such as extra-high hormone levels or quick pregnancy progression.

Doctors are also trained to detect the differences in the symptoms that show in a typical pregnancy compared to one producing twins. Imagine two women are pregnant at the same time. One is carrying one baby and the other is carrying twins. Both mothers will experience morning sickness, weight gain and heartburn, but the mother carrying twins will have more severe symptoms. She may gain 10 more pounds than the other mom, deal with extreme morning sickness or be fatigued at all hours of the day. Her doctor will know to pay attention to these small details at checkups and recognize what they’re indicating.

So, unless other genetic factors make you more likely to have twins, you typically have nothing to worry about. The later in your pregnancy you are, the harder it becomes for a twin to hide from you and your doctor — or from its sibling.

Should You Be on the Lookout for Hidden Twin Syndrome?


If you’re wondering about the possibility of having twins, and you’re still waiting on a later ultrasound result to confirm the number of babies you’ll be welcoming into your home, there are a few factors you might consider.

Some of the most significant factors that impact the likelihood of having twins are age and use of fertility treatment. Women over 35 are more likely to have twins because they are more likely to release multiple eggs during one cycle. That fact may seem contradictory, as older women are told that advancing age makes it less likely for them to get pregnant. That’s true too, but on the less frequent chance of ovulation, it’s more likely that multiple eggs will be released. If you’re older — sorry, ladies — you might want to be on the lookout for twins during your ultrasounds.

Fertility treatment can increase the likelihood of having twins. This is especially true if you are using fertility drugs, as they can also cause you to release multiple eggs during one cycle. If you’re wondering how your fertility treatment may affect your chances of having twins, consult your doctor sooner rather than later. National data shows that women who used in vitro fertilization (IVF) after the age of 35 had only a 2.6 percent lesser chance to conceive twins than women under 35.

A common detail that women tell each other is that you’re more likely to have twins if it’s in your genes. This idea has been proven true, as genetic factors can cause women to have hyperovulation. Figuring out a single gene that leads to twins is difficult because genetics is a complex subject, but links have been found to both identical and fraternal twins.

Other factors including heredity, history of twins and stature can all make you more or less likely to have twins. Evaluating your likelihood using these factors may help put your mind at ease if you’re worried about twins discovered late in pregnancy. However, this line of thinking shouldn’t be a substitute for a professional, thorough ultrasound.

Will You Be Bringing Home a Second Baby Unexpectedly?


The short answer is: no, probably not. Twins are very rarely missed on ultrasounds — even when they are overlooked early on, they tend to become easily identifiable after a few months. If you’re going to be having twins, you’ll know about it long before you deliver. Don’t let the surprise twist-endings of movies make you believe otherwise — those story lines are written to create more drama for a reason.

If you do happen to be one of the few legendary people who discover secret twins during your pregnancy, take comfort in that you’ll still have plenty of time to prepare the nursery. Just be sure to give the little ones enough space when they finally arrive — it can’t be easy sharing space in the same belly for nine months!

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