When babies are born, they exhibit a range of innate reflexes that are designed to help them navigate this strange new world that they’ve just entered.

Most people are familiar with primitive reflexes such as rooting that help babies find the breast or bottle for feeding or even the Moro reflex — more commonly known as the startle reflex — which can even be triggered by a baby’s own cry.

But are you familiar with the asymmetrical tonic neck reflex (ATNR)? What is the purpose of this reflex and when do babies outgrow it?

ATNR is an acronym that stands for asymmetrical tonic neck reflex. It’s a primitive reflex that babies exhibit and is part of the development of muscle tone, consistent one-sided movements with their body, and even proper hand-eye coordination.

In infants, ATNR sometimes occurs when a baby turns their head, but usually isn’t one of the more obviously identified reflexes that parents or caregivers will see. Most often, it’s actively engaged by doctors testing for this reflex.

When a physician turns your baby’s head, the arm and leg on the side where their head is turned are also extended. ATNR is also referred to as the fencer’s reflex because when this reflex is observed, it looks like your little one is holding a fencer’s pose.

ATNR begins while your baby is in the womb and can even be seen as early as 18 weeks during pregnancy. This reflex may help babies move through the birth canal during vaginal deliveries.

ATNR begins in the womb but usually disappears between 5 to 7 months of age when your baby is likely mastering more complex motor skills such as sitting up.

Keep in mind that it could take up to a child’s first year for ATNR to fully integrate. Integrated ATNR means that while your baby is awake, they won’t automatically display the fencer’s pose when their head is turned while laying down.

But for some babies, ATNR doesn’t integrate properly — meaning that they still exhibit this reflex beyond this average timeline — and it can be associated with developmental delays. This condition is known as retained ATNR.

Generally, if your baby continues to show ATNR after 7 months, it’s considered atypical development.

Some researchers have theorized that retained ATNR is linked to potential developmental delays that could present themselves for years after infancy. This is a controversial subject, as noted in a 2019 continuing education module offered by the American Occupational Therapy Association.

While there is little clinical research looking specifically at ATNR reflexes, studies in 2004 and 2007 found that retained ATNR may negatively affect children’s reading capabilities.

Some issues that some medical experts believe may be linked to retained primitive reflexes include:

  • poor hand-eye coordination, especially when writing
  • difficulty with visual tracking
  • difficulty with handwriting, including an excessively tight grip
  • struggling to translate ideas into written text
  • dyslexia

This 2013 review notes that an older study from 1984 found a link between retained primitive reflexes and delayed motor development in very low birthweight babies.

A 2018 study found that children ages 4 to 6 who retained primitive reflexes exhibited reduced motor development skills. Researchers tested the children on such skills as jumping sideways, carrying balls to and from a box, and placing dots on a sheet.

Obviously, there’s a large time gap between when your baby should have integrated ATNR and when they might experience some of the more obvious reading and writing developmental delays.

Keep in mind that delays in achieving developmental milestones aren’t always a sign that there’s something wrong, and there’s no definitive consensus within the medical community that prolonged ATNR is linked to or causes developmental delays.

Those who do believe that there’s a link between non-integrated ATNR and developmental delays propose there may be early signs to signify your baby or toddler might need help to integrate their ATNR and minimize potential developmental or learning delays. These signs include:

  • poor balance while sitting or standing when your baby moves their head from side to side
  • struggling to cross the midline of their body with their arms and legs
  • jerky eye movements

In older children, you might see the following signs:

  • difficulty throwing or catching a ball
  • struggling with handwriting
  • using an extremely tight pencil grip
  • using both hands to write interchangeably
  • having trouble to learning to ride a bike
  • difficulty paying attention
  • struggling to multitask
  • mixing up letters like “b” and “d”

Keep in mind that the correlation between a non-integrated ATNR and these symptoms is just theory. You’ll want to speak with your doctor about the best course of treatment specific to your child’s unique situation.

In babies, an atypical presentation of ATNR may be explored if your baby struggles to maintain balance or has difficulty with visual tracking.

In older children, you may notice some of the signs noted in “signs and symptoms” section above.

If you have any concerns about your child’s development, speak with your pediatrician. They may recommend an evaluation by an occupational therapist.

If the therapist agrees that ATNR hasn’t integrated, they may work with your child by performing simple exercises, games, and activities designed for your child’s age.

The goal is to create movements that mimic the early reflex movements and create new learned neural pathways to help integrate ATNR.

Note, again, that not all occupational therapists believe there is a link between developmental delays and presence of retained primitive reflexes like ATNR.

Until further research clearly identifies a link, your doctor will likely explore several potential causes and treatments for the symptoms your child presents.

ATNR is one of many reflexes that is present when babies are born. While some in the medical community suggest that there’s a direct link between retained ATNR and developmental delays, the research around this theory is still in its infancy.

If you’re concerned that your child might be exhibiting developmental delays of any kind, it’s always a good idea to speak with your child’s pediatrician.