What is skeletal dysplasia?

Skeletal dysplasia is a term used to describe a group of several hundred conditions that affect the formation and growth of a baby’s bones and cartilage. Some of the conditions result in the child’s arms and legs being disproportionately small in size when compared with the torso and head. These abnormalities may result in the child having a very short stature, or “dwarfism.” In some types of skeletal dysplasia the bones may become demineralized, or brittle, causing them to break easily, even before birth. This malformation of the bones can also lead to abnormal bone shapes.

Certain skeletal dysplasia conditions can be fatal. These deaths occur when the bony chest cavity fails to grow normally, preventing normal lung development and resulting in lungs that are too small to support the baby’s breathing after birth—a condition known as lethal pulmonary hypoplasia.

Here are some of the more common types of skeletal dysplasia:

• Achondroplasia is a type of short-limbed dwarfism. Children with achondroplasia have short forearms and legs, a large head, and an average-sized torso. The condition, which occurs in about 1 in 40,000 births, does not affect the child’s intelligence or lifespan.
• Osteogenesis imperfecta, sometimes called “brittle bone disease,” is a term that encompasses a group of conditions characterized by bones that break easily, sometimes from no obvious cause. The conditions range from mild to severe, and may or may not result in a curved spine and small stature. Milder forms of osteogenesis imperfecta do not affect the child’s lifespan.
• Achondrogenesis is a group of skeletal dysplasia conditions that severely affect bone formation. In addition to having short arms and legs, babies with achondrogenesis have a small, narrow chest and underdeveloped lungs. As a result, these babies usually do not survive long after birth.
• Campomelic dysplasia is a usually lethal skeletal dysplasia typified by severe bowing of the long bones. It is also associated with disorders of sexual development as it is caused by genetic mutations that affect the development of both cartilage and the testes.
• Short-rib polydactyly syndrome is a group of skeletal dysplasia conditions in which the growth of the baby’s bones is severely affected, resulting in short arms and legs, short ribs, and more than the normal number of fingers and/or toes. Because of their small, narrow chests, all babies with short-rib polydactyly syndrome have severe pulmonary hypoplasia, which prevents their survival after birth.

Each of the hundreds of skeletal dysplasia conditions is relatively rare, but collectively they affect about 1 in 4,000 births.

Who will be on my care team?

At the Midwest Fetal Care Center, a collaboration between Children’s Minnesota and Allina Health, we specialize in individual attention that starts with you having your own personal care coordinator to help you navigate your baby’s treatment process. We use a comprehensive team approach to skeletal dysplasia and any associated conditions. That way, you are assured of getting the best possible information by some of the most experienced physicians in the country.

For skeletal dysplasia, your care team will include a maternal-fetal medicine specialist, a neonatologist, a geneticist, a nurse specialist care coordinator, a fetal care clinical social worker, and several other technical specialists. This comprehensive team will follow you and your baby closely through the evaluation process and will be responsible for designing and carrying out your complete care plan.

What causes skeletal dysplasia?

Most of these conditions result from a defective gene that interferes with cartilage and bone development. The genetic mutations are sometimes passed down to children from their parents, but a vast majority of the mutations happen randomly. About 80 percent of children born with achondroplasia, for example, have average-sized parents.

How is skeletal dysplasia diagnosed?

The first indication that a baby has a skeletal dysplasia condition may arise during a routine prenatal ultrasound examination, usually one conducted in the second trimester of pregnancy. The image may show arms and legs shorter than average and a head larger than average. Or it may show that the baby’s bones are abnormally shaped in other ways—or that they are less dense than normal. Sometimes, fractures can be seen on the ultrasound. Another possible sign of skeletal dysplasia is the presence of excess amniotic fluid (polyhydramnios). Certain types of skeletal dysplasia cannot be identified until later in pregnancy as they result from an abnormal bone formation that takes place mostly in the second half of pregnancy, after the timing of routine scans.

Level II ultrasound

If a skeletal dysplasia condition is suspected, your obstetrician-gynecologist (ob-gyn) will recommend a specialized type of ultrasound known as a Level II scan, which will create more detailed images of your baby’s bones and other organs. This procedure is usually conducted by a maternal-fetal medicine specialist (an ob-gyn who specializes in caring for women with complicated pregnancies).

Genetic testing

Prenatal DNA (genetic) testing may also be recommended. Such testing can sometimes confirm the diagnosis of a skeletal dysplasia and may even help identify which kind it is.

There are two basic types of prenatal DNA testing: amniocentesis and chorionic villis sampling (CVS). Both procedures can be done in our clinic. Amniocentesis is performed during the second or third trimester of pregnancy. A small needle is placed through the mother’s abdomen and into the amniotic sac surrounding the baby to obtain a sample of the amniotic fluid, which contains many fetal cells. The genetic material in the sample’s cells is then analyzed for evidence of skeletal dysplasia-related mutations. CVS is a similar procedure, but it obtains its sample from cells in the placenta rather than from those in the amniotic fluid. It is usually done during the first trimester and can help give an early diagnosis in cases at risk of a potential lethal skeletal dysplasia.

Some types of skeletal dysplasia, however, may not be evident until birth.

How is skeletal dysplasia managed before birth?

If your baby is diagnosed with skeletal dysplasia before birth, you will be referred to a fetal care center, such as the Midwest Fetal Care Center, for the management of your pregnancy and delivery. That management starts with acquiring as much information about your baby’s condition as possible. The information will initially come from a Level II scan and, perhaps, an amniocentesis, as well as from consultations with a maternal-fetal medicine specialist and a geneticist. Prenatal tests and assessments are used to identify, if possible, which type of skeletal dysplasia the baby has, as that factor is the strongest indicator of an infant’s outcome. Determining the lethality of the condition is paramount, as this will help guide other decisions through the pregnancy.

If there is uncertainty about the diagnosis, your doctors may recommend magnetic resonance imaging (MRI) in order to obtain more information about your baby’s condition. Like ultrasound, fetal MRI is a non-invasive test. It uses a large magnet, pulses of radio waves, and a computer to create detailed images of your baby’s organs and other structures while in the womb. This procedure involves both mom and baby being scanned inside our MRI machine. The test is a bit loud, but it takes only about 30 minutes and is not uncomfortable.

How is skeletal dysplasia treated after birth?

Our goal will be to have your baby’s birth occur as near to your due date as possible. Many babies with skeletal dysplasia can be born vaginally, but a cesarean delivery is often necessary.

Babies with skeletal dysplasia frequently require medical care immediately after birth. For that reason, your baby will be born at The Mother Baby Center at Abbott Northwestern and Children’s Minnesota in Minneapolis or at The Mother Baby Center at United Hospital and Children’s Minnesota in St. Paul. Children’s Minnesota is one of only a few centers nationwide with a birth center located within the hospital complex. This means that your baby will be born just a few feet down the hall from our newborn intensive care unit (NICU). Also, many of the physicians you have already met will be present during or immediately after your baby’s birth to help care for your baby right away.

Your child’s treatment after birth will depend on the type and severity of their skeletal dysplasia. It may include bracing (to correct curvature of the spine and bowing of the lower legs), physical therapy, growth hormone therapy, and/or surgery. Treatments for skeletal dysplasia focus on reducing the risk of medical complications associated with the condition.

What is my baby’s prognosis?

Your baby’s prognosis will depend on the type and severity of their condition. About half of infants with skeletal dysplasia are stillborn or die soon after birth. But many—including most with achondroplasia—lead full, happy, and productive lives.

Will my baby need long-term follow-up care?

Most children with a skeletal dysplasia will need lifelong medical care for various health issues related to their condition. The form and frequency of this follow-up care will depend on the type and severity of the skeletal dysplasia condition.