Premature Birth and Hip Health: What Parents Need to Know
"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.
Preterm Hip Findings
Research identifies the 30th, 31st, 32nd, and 34th weeks of gestation as ages that warrant consideration of dysplastic and subluxed hips in premature newborns. Studies have examined the prevalence of developmental dysplasia of the hip (DDH) in preterm infants, including those with maternal risk factors, using medical records and ultrasound scans. A population-based study compared hip-ultrasound findings in 2,534 term infants and 376 preterm infants, reflecting ongoing efforts to clarify incidence differences between the groups.
Surveillance and Early Assessment
DDH covers a spectrum ranging from mild developmental abnormalities to frank dislocation, and clinical hip instability occurs in 1% to 2% of full-term infants, while imaging can detect hip instability or immaturity in up to 15%. Accepted evaluation relies on clinical assessment and imaging, including ultrasound or radiography, while recognizing that early hip development can be physiologic. The American Academy of Pediatrics report was reaffirmed in June 2021, and a 2023 Johns Hopkins pathway emphasizes that dysplasia may develop in utero, around birth, or during infancy and childhood, making continued surveillance important.
The Gestational Age Factor: Why It Matters for Hip Development
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.
- 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.
What Recent Reviews Show
A systematic review and meta-analysis titled "Preterm birth does not increase the risk of developmental dysplasia of the Hip" evaluated studies of the association between preterm birth and DDH. Another meta-analysis included preterm births from 23 to 36 weeks of gestation and term births at 37 weeks or more. The evidence remains mixed: one 2025 screening study reports that a prior meta-analysis concluded prematurity may be protective, while also citing research in which DDH incidence was higher among premature infants.
Evidence and Screening Gaps
The 2023 systematic review searched Medline, Embase, Scopus, and Web of Science for studies concerning DDH and preterm birth, then analyzed the data using RevMan5 and Comprehensive Meta-Analysis. Separate research reviewed the incidence of DDH in preterm breech infants at a single quaternary-care urban medical center. Because that study covered infants born at one institution between 2012 and 2022 and also examined provider screening practices, its findings highlight how local practice and population differences can complicate broader conclusions.
Birth Weight Context
The Chinese neonatal birth-weight curve study reported a mean birth weight of 3,232 ± 555 g. Mean birth weight was 3,271 ± 576 g for male newborns and 3,188 ± 528 g for female newborns. The study reported that gestational-age and birth-weight distributions did not fit a normal distribution and were best represented by a BCT distribution.
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.
Evolving Hip Care
A 2026 Children's Hospital Los Angeles article identifies seven trends reshaping pediatric hip dysplasia care. It states that timely treatment can substantially improve the lives of babies and teens with hip dysplasia. The article also emphasizes that early, specialized care may help children remain active and pain-free, whereas some may otherwise face surgery, limited mobility, or early hip replacement.
From Infant Care to Function
A case report describes hip mobilization in a preterm infant born at 33 6/7 weeks of gestational age who was diagnosed with DDH. The report notes that few studies have described mobilization approaches for DDH and follows the infant during a 43-day hospital stay. Another case report characterizes DDH as a spectrum from mild dysplasia to severe dislocation, with consequences for biomechanics and joint stability, underscoring why individual assessment and follow-up matter.