Head Shape Deformity in Twins: Why Is It More Common?



Head Shape Deformity in Twin Babies: Why It Is More Common

Quick answer: Head shape deformity (plagiocephaly or brachycephaly) is significantly more common in twins due to intrauterine crowding, frequent premature birth, and positional constraints after delivery. Both twins can be fitted with helmets at the same appointment at CranioWell.

Statistics show that the rate of head shape deformity in twins is much higher than in singleton pregnancies. What causes this — and what can be done about it? At CranioWell Orthopedic & Prosthetic Centers, we have examined this special situation in multiple pregnancies and the solutions available.

1. The Main Cause: Intrauterine Crowding

In a singleton pregnancy, the baby has relatively ample space to move and float inside the womb. In twins or higher-order multiples, however, the space is shared — and movement becomes increasingly limited as the final months of pregnancy approach.

In medical terminology this is called "Intrauterine Constraint."

• The babies fit together like puzzle pieces.
• One baby's head may be forced to rest against the other baby's body or against the mother's pelvis.
• This constant pressure on the soft skull bones can produce a head shape deformity even before birth.

2. The "Mirror Image" Effect

An interesting pattern we frequently see in twins is Mirror Image Plagiocephaly. Due to their intrauterine positions, one twin typically rests with the head to the right while the other is forced to turn left.

• As a result, one twin may develop flattening on the right side while the other develops flattening on the left.
• After birth, babies tend to continue resting in the same position they became accustomed to in the womb.

3. The Premature Birth Factor

As discussed in our premature baby article, premature babies have significantly softer bones. Approximately 60% of twin pregnancies result in premature delivery.

• Softer Bones: More vulnerable to external pressure.
• NICU Period: If intensive care is required, fixed positioning significantly increases the risk. When these two factors combine, the risk of head shape deformity in twins multiplies.

4. Higher Rate of Torticollis

The cramped intrauterine position affects not only the skull bones but also the neck muscles. The baby remaining for an extended period with the neck flexed or rotated can cause shortening of the SCM muscle. After birth, the baby struggles to turn the head to the other side and continues resting on the same spot. This causes existing flattening to progress. The incidence of torticollis in twins is higher than in singletons.

Practical Challenges of Twin Care

Caring for twins is physically demanding. While attending to one baby (feeding, nappy change), the other must wait safely — often in a bouncer or pram. These waiting periods can increase the time during which pressure is applied to the back of the head. This is not parental negligence; it is an inevitable practical reality.

What Can Be Done for Twins?

1. Plenty of Tummy Time: Encourage tummy time whenever both babies are awake. Positioning them face to face can be motivating for both.
2. Repositioning: Alternating which end of the cot each baby sleeps toward can help redirect attention and head position.
3. Helmet Therapy (Cranial Orthosis): If flattening is moderate or severe, helmet therapy delivers very successful results for twins. At CranioWell, both babies can be assessed and measured at the same appointment, supporting family time management.

---

Frequently asked questions

Only one of our twins has flattening — is that normal?

Yes, this is very common. One baby may have been more constrained in the womb (for example pressing against the pelvis). Each baby's degree of involvement varies.

Is helmet therapy difficult with twins?

Managing two babies is challenging in itself, but helmet therapy does not add a significant extra burden. Babies adapt to their helmets very quickly. In fact, helmets act as a protective barrier, preventing babies from bumping heads against each other during crawling and play.

Is head shape deformity genetic in twins?

Head shape deformity (Plagiocephaly) is generally not genetic but positional (caused by external pressure). Its higher occurrence in twins is due to space constraints, not genetics.

---

At CranioWell Orthopedic & Prosthetic Centers, we stand by twin families with our specialist approach and 3D scanning technology. We can measure both babies at the same appointment, quickly and without causing distress.