Illustration of healthy hip development in infants

Premature Birth and Hip Health: What Parents Need to Know

Beau Callahan in Health & Wellness December 2025 • 4 min read.

"A new study explores how gestational age impacts hip development in preterm infants, offering crucial insights for early screening and care."

Developmental dysplasia of the hip (DDH) refers to a spectrum of conditions where the hip joint doesn't form properly. This can range from mild instability to complete dislocation, where the ball of the thighbone (femoral head) isn't properly seated in the hip socket (acetabulum). Early detection and intervention are key to preventing long-term complications like limping, pain, and arthritis.

Ultrasound has become a vital tool for screening newborns for DDH. The Graf method, a standardized ultrasound technique, allows doctors to assess the angle and stability of the hip joint. By measuring specific angles, clinicians can classify hips as normal, immature, dysplastic, or dislocated, guiding appropriate treatment decisions.

While ultrasound screening is widely used, questions remain about the unique challenges posed by premature birth. Premature infants have different developmental timelines than full-term babies, and it’s not always clear how gestational age affects the accuracy and interpretation of hip ultrasounds. A recent study aimed to shed light on this issue, investigating the relationship between gestational age and hip ultrasound findings in preterm newborns.

The Gestational Age Factor: Why It Matters for Hip Development

Illustration of healthy hip development in infants

The study, published in the Journal of Pediatric Orthopaedics B, retrospectively examined 788 hips of 394 premature newborns born between 30 and 36 weeks of gestational age. All infants underwent hip ultrasonography within their first week of life. Researchers analyzed the distribution of hip types and roof angles (alpha and beta angles) in relation to gestational age and sex.

Here’s a breakdown of the key findings:

Specific Gestational Ages at Higher Risk: The study identified the 30th, 31st, 32nd, and 34th weeks of gestation as periods where dysplastic and subluxed hips were more commonly observed in preterm infants. This suggests that babies born during these weeks may require closer monitoring.
Sex Differences: In the 30th week, type IIc hips (a type of immature hip) were more prevalent in females, while type III hips (subluxated hips) were more common in males. In the 34th week, type IIc hips were again more frequent in males. These sex-specific differences highlight the importance of considering gender in ultrasound interpretation.
Type IIa Hips: In the 35th week, type IIa hips were statistically significantly higher in female hips.
Overall Hip Type Distribution: Across all gestational ages, type IIc hips were most frequent in the 30th, 31st, 32nd, and 34th weeks. Type III hips were statistically significantly more common in the 30th week.
Angle Variations: The mean alpha angle (a key measurement in hip ultrasound) was significantly lower in the 30th-week group compared to infants born in the 33rd, 34th, 35th, and 36th weeks. This indicates a less mature hip socket in the earliest gestational age group.

These findings suggest that hip development in preterm infants is not uniform and can be influenced by gestational age. Babies born earlier may have a higher risk of hip instability or dysplasia, necessitating careful evaluation.

What This Means for Parents and Healthcare Providers

This study underscores the importance of awareness regarding the potential impact of gestational age on hip development. While prematurity itself isn't necessarily a cause of DDH, it appears to create a window of vulnerability where hip development may be less stable. Therefore, early ultrasound screening, particularly for infants born between 30 and 34 weeks, is crucial.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1097/bpb.0000000000000541, Alternate LINK

Title: Does Gestational Age Affect Ultrasonographic Findings Of The Hip In Preterm Newborns? A Sonographic Study Of The Early Neonatal Period

Subject: Orthopedics and Sports Medicine

Journal: Journal of Pediatric Orthopaedics B

Publisher: Ovid Technologies (Wolters Kluwer Health)

Authors: Altuğ Duramaz, Burcu B. Duramaz, Mustafa G. Bilgili

Published: 2019-03-01

Everything You Need To Know

What is Developmental dysplasia of the hip (DDH), and why is it important for newborns?

Developmental dysplasia of the hip (DDH) is a condition where the hip joint doesn't form correctly. This can range from mild instability to complete dislocation, where the ball of the thighbone (femoral head) is not properly seated in the hip socket (acetabulum). If left untreated, DDH can lead to long-term problems like limping, pain, and arthritis. Early detection through ultrasound screening is critical to ensuring healthy hip development and preventing these complications.

What is the Graf method, and how does it help in assessing hip health?

The Graf method is a standardized ultrasound technique used to assess the angle and stability of the hip joint in newborns. Clinicians use the Graf method to measure specific angles, like the alpha and beta angles, to classify hips. Based on these measurements, hips are categorized as normal, immature, dysplastic, or dislocated. This classification guides treatment decisions. The Graf method helps doctors identify early signs of Developmental dysplasia of the hip (DDH) and provides a framework for consistent evaluation, improving the accuracy and effectiveness of early intervention.

Why is gestational age significant when considering hip development in premature babies?

Gestational age is a crucial factor because it influences the timing of hip development, particularly in preterm infants. The study identified that specific gestational ages, such as the 30th, 31st, 32nd, and 34th weeks, show a higher occurrence of dysplastic and subluxed hips. These findings mean that infants born within these weeks might need more careful monitoring. Premature babies have different developmental timelines compared to full-term babies. Therefore, understanding the connection between gestational age and hip development is essential to determine the risk level of Developmental dysplasia of the hip (DDH).

How do sex differences affect hip development in preterm infants?

The study observed sex-specific differences in hip development. For example, in the 30th week of gestation, type IIc hips were more prevalent in females, while type III hips were more common in males. In the 34th week, type IIc hips were again more frequent in males. In the 35th week, type IIa hips were statistically significantly higher in female hips. The differences highlight the importance of considering gender in ultrasound interpretation. This emphasizes the necessity for tailored screening and care based on the infant's sex.

Why is early ultrasound screening recommended for premature babies?

Early ultrasound screening is crucial, particularly for infants born between 30 and 34 weeks of gestation. Ultrasound screening allows for early detection of Developmental dysplasia of the hip (DDH), enabling prompt intervention. Regular hip ultrasounds help in the early diagnosis of DDH, leading to timely treatments that can prevent serious long-term consequences. The study underscores the importance of awareness and the need for proactive screening programs to safeguard the hip health of preterm infants.