The Relationship Between Finger Ratio and Development in Infants

The Relationship Between Digit Ratio and Motor Development and Sensory Processing in Infants

One of the most prominent indicators of prenatal androgen exposure is considered to be the ratio of second and fourth finger lengths (2D:4D). The 2D:4D finger ratio refers to the ratio of the length of the second finger (2D; index finger) and the fourth finger (4D; ring finger). Evidence suggests that 2D:4D is developmentally stable and stabilizes from the second trimester of pregnancy. It has been reported that the 2D:4D ratio correlates positively with estrogen and negatively with testosterone. In both sexes, prenatal testosterone levels are inversely related by a 2D:4D ratio, which does not change with age. Androgens can have direct trophic effects on target cells or indirectly affect neuronal growth through neurotrophic mediators released locally by steroid-sensitive neuronal or glial cells. Prenatal testosterone can have long-term organizational effects on the structure and function of various body systems (e.g., cardiovascular and musculoskeletal systems) that are important for physical activity and exercise.

Study Overview

• Status: Recruiting
• Conditions: Infant Developmental Assessment
• Intervention / Treatment: Behavioral: Digit Ratio; Behavioral: Motor development; Behavioral: Sensory processing functions

Detailed Description

One of the most prominent indicators of prenatal androgen exposure is considered to be the ratio of second and fourth finger lengths (2D:4D). The 2D:4D finger ratio refers to the ratio of the length of the second finger (2D; index finger) and the fourth finger (4D; ring finger). Evidence suggests that 2D:4D is developmentally stable and stabilizes from the second trimester of pregnancy. It has been reported that the 2D:4D ratio correlates positively with estrogen and negatively with testosterone. In both sexes, prenatal testosterone levels are inversely related by a 2D:4D ratio, which does not change with age.

From a gender perspective, differences have been found in the basic motor skills of boys and girls. Boys have greater object control skills than girls. Gender is one of the most studied variables in motor development. Many longitudinal studies show that boys perform better in gross motor skills such as running and jumping, while girls are more successful in fine motor tasks such as drawing or manipulating small objects. Sensory processing involves the capacity to receive, interpret, organize, and respond to sensory input from both one's own body and the external environment. Sensory processing disorders can be observed in infants due to the immaturity of their systems. There are very few studies on measuring finger length in the early stages of newborns. To our knowledge, the relationship between intrauterine androgen exposure (2D:4D) and motor development and sensory processing has not yet been investigated. Therefore, the planned study aims to evaluate the 2D:4D finger ratio in 12-18-month-old infants and to examine the relationship between this ratio and motor development and sensory processing.

• Study Type: Observational
• Enrollment (Estimated): 80

Contacts and Locations

• Study Contact: Name: Rabia ZORLULAR; Phone Number: +5424362082; Email: rabiaeraslan118@gmail.com
• Study Contact Backup: Name: Rabia Zorlular; Email: rabiaeraslan118@gmail.com

Study Locations

• Turkey (Türkiye)
  • Niğde, Turkey (Türkiye)
    • Recruiting
    • Nigde Omer Halisdemir University
    • Contact: Rabia ZORLULAR; Phone Number: +5424362082; Email: rabiaeraslan118@gmail.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child
• Accepts Healthy Volunteers: Yes

• Sampling Method: Non-Probability Sample

Study Population

The study will include healthy, full-term (37-40 weeks of gestation) infants aged 12 to 18 months.

Description

Inclusion Criteria:

• Term infants (37-40 weeks),
• Infants aged 12-18 months

Exclusion Criteria:

• Preterm infants,
• Infants with congenital infections or proven genetic changes,
• Infants and mothers diagnosed with metabolic, neurological, and genetic diseases,
• Maternal diabetes,
• Intrauterine growth retardation,
• Infants with a history of hand-related surgery,
• Children whose parents did not volunteer to study

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort

Intervention / Treatment

Healthy infants; Healthy, full-term (37-40 weeks of gestation) infants aged 12 to 18 months and their families will be invited to participate in the study.

Behavioral: Digit Ratio; The lengths of the second (2D) and fourth (4D) fingers will be measured separately on each hand. Measurements will be taken with the baby's hands placed flat on a surface with palms facing upwards. Finger length will be defined as the distance from the midpoint of the proximal crease at the base of the finger to the distal end of the finger. A digital caliper with a precision of 0.01 mm will be used, and two separate measurements will be taken for each finger, with the average value recorded. Based on these measurements, the 2D:4D finger ratio for each hand will be calculated by dividing the length of the second finger by the length of the fourth finger.; Behavioral: Motor development; The Peabody Developmental Motor Scale-2 (PDMS-2) is planned to be used to assess motor development. The PDMS-2 test is designed to identify developmental delays in children aged 0-72 months. It is used to evaluate children's motor development with separate tests and rating scales for both gross and fine motor skills.; Behavioral: Sensory processing functions; The Test of Sensory Functions in Infants was planned for use to assess babies' sensory development. The TSFI is frequently used to evaluate the sensory processing functions of infants aged 4-18 months. It is used to determine whether and to what extent a baby has a sensory processing problem. It consists of 24 items. The TSFI requires the baby to be stimulated and interact with various materials. The total score ranges from 0-49, and the test has normative values for different age groups. Although it can be used from the fourth month onwards, the most reliable and valid results are obtained between 7-18 months.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Digit Ratio	The lengths of the second (2D) and fourth (4D) fingers of the participants will be measured separately on each hand. Measurements will be taken with the participants' hands placed flat on a surface with the palms facing upwards. Measurements will be performed using a digital caliper with a precision of 0.01 mm, two separate measurements will be taken for each finger, and the average value will be recorded. Based on the obtained measurements, the 2D:4D finger ratio will be calculated by dividing the 2D length by the 4D length on both hands. To increase the reliability of the measurements, the assessments will be performed twice by a researcher who is blind to motor development and sensory processing skills.	12-18 months
Sensory processing	The Test of Sensory Functions in Infants is a standardized assessment tool designed to evaluate sensory processing abilities in infants aged 4 to 18 months. The TSFI examines responses across multiple sensory domains, including tactile, vestibular, visual, and oral-motor functions, providing a comprehensive profile of an infant's sensory processing. In the tactile deep pressure response section, it is scored as 0: reverse response, 1: mild defensive response, and 2: integrated response. In the adaptive motor response section, it is scored as 0: no response, 1: disorganized, 2: partial, 3: organized. In the visual-tactile integration section, it is scored as 0: hyperactive, 1: hyporeactive, and 2: normal. The oculomotor test section is scored as 0: no response or poorly integrated, 1: well integrated. Response to vestibular stimulation is scored as 0: adverse response, 1: mild defensive response, and 2: integrated response. The total score ranges from 0 to 49.	12-18 months
Motor development	The Peabody Developmental Motor Scales, Second Edition, is a standardized tool used to assess gross and fine motor skills in children from birth to 5 years of age. The assessment comprises six subtests: reflexes, stationary, locomotion, object manipulation, grasping, and visual-motor integration, which together provide a comprehensive evaluation of a child's motor development. It has been widely validated in both typically developing children and those with various developmental disorders, making it a reliable and widely used instrument in pediatric motor assessment. Items are scored with 0, 1, and 2 points. When the child performs the item according to the specified item criteria, 2 points are given. One point is awarded when the behavior occurs, but the criteria for successful performance are not fully met. A score of 0 is given when the child is unable to try the item or does not reveal any skills when he tries it. Results are expressed as raw, standard, or total motor scores.	12-18 months

Collaborators and Investigators

• Sponsor: Nigde Omer Halisdemir University
• Investigators: Principal Investigator: Rabia ZORLULAR, Nigde Omer Halisdemir University

Publications and helpful links

General Publications

• Cay M, Gurel S. The relationship between mothers' second and fourth finger lengths (2D:4D) and anthropometric measurements (height, weight, head circumference, and 2D:4D) of the newborns. Am J Hum Biol. 2022 May;34(5):e23700. doi: 10.1002/ajhb.23700. Epub 2021 Nov 9.
• Ernsten L, Korner LM, Heil M, Schaal NK. The association between 2D:4D digit ratio and sex-typed play in children with and without siblings. Sci Rep. 2024 Jul 2;14(1):15231. doi: 10.1038/s41598-024-65739-1.
• Paukner A. Digit ratio (2D:4D) and its behavioral correlates in infant rhesus macaques (Macaca mulatta). Dev Psychobiol. 2020 Nov;62(7):992-998. doi: 10.1002/dev.21917. Epub 2019 Sep 12.

Study record dates

Study Major Dates

• Study Start (Actual): April 6, 2026
• Primary Completion (Estimated): April 1, 2027
• Study Completion (Estimated): April 1, 2027

Study Registration Dates

• First Submitted: April 6, 2026
• First Submitted That Met QC Criteria: April 6, 2026
• First Posted (Actual): April 13, 2026

Study Record Updates

• Last Update Posted (Actual): May 8, 2026
• Last Update Submitted That Met QC Criteria: May 4, 2026
• Last Verified: April 1, 2026

More Information

Terms related to this study

• Keywords: motor development; infant; sensory processing; digit ratio; 2D:4D ratio; Prenatal androgen
• Additional Relevant MeSH Terms: Investigative Techniques; Diagnostic Techniques and Procedures; Diagnosis; Public Health; Environment and Public Health; Epidemiologic Measurements; Physical Examination; Body Weights and Measures; Anthropometry; Biometry; Digit Ratios
• Other Study ID Numbers: Digit ratio and development

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No