Does second-to-fourth digit length ratio (2D:4D) predict age at menarche in women?

Association patterns between 2D:4D ratio and age at menarche: the impact of methodology

The ratio of index finger to ring finger length (2D:4D) is a sexually dimorphic feature and widely used as an indicator of prenatal androgen-estrogen exposure. Several studies have investigated the relationship between the 2D:4D ratio and the onset of the first menstrual period (menarche) in women.

The present study tested the association patterns between 2D:4D ratio and age at menarche. Furthermore, the impact of methods of measuring finger lengths was considered.

Two samples were used to conduct the study. One sample consisted of 110 women who self-measured their finger lengths. The finger length measurements in the second sample (88 women) were taken from one trained observer using the caliper-based technique. Age at menarche was determined using a retrospective method.

Women from the first sample reported an average age for the onset of the first menstrual bleeding at 12.9 (SD = 1.4) years of age. There was no significant association between the left and right 2D:4D ratio and the age at menarche. The second sample showed a mean age at menarche at 12.8 (SD = 1.3) years of age. Here, the right hand 2D:4D ratio and age at menarche were significantly correlated (p<0.001).

A more feminine 2D:4D ratio was significantly associated with an earlier menarcheal age only in the sample with direct finger length measurements by a trained investigator. The sample using self-measurements yielded no significant associations between menarcheal age and 2D:4D. The use of a reliable and well-founded methodology is essential for obtaining meaningful results.

Effects of hand preference on digit lengths and digit ratios among children and adults

BACKGROUND

Prenatal sex hormones may not exclusively determine effects of hand preference on digit ratios. Genetic determination is an alternative possibility.

AIM

To study the likelihood of similar effects of hand preference on digit lengths and digit ratios.

METHODS

We selected similar numbers of left-handers and right-handers in samples of kindergarten children (N = 101, age range: 3.5-7 years) and adults (N = 189, age range: 17-28 years) and measured digit lengths (excluding the thumb) directly on the palmar hand.

RESULTS

Compared to right-handers, left-handers had longer digits and lower third-to-fourth (3D:4D) digit ratios among children, whereas an opposite pattern of handedness differences occurred among adults.

CONCLUSIONS

Effects of hand preference on digit lengths and ratios might be genetically/ontogenetically determined. Also discussed are implications of this set of findings for digit ratio research.

The association between second to fourth digit ratio, reproductive and general health among women: findings from an Israeli pregnancy cohort

The ratio between the length of second and fourth digits (2D:4D) is a putative biomarker for prenatal testosterone and estrogen exposure. The aim of the study was to examine the association between 2D:4D and women’s general and reproductive health. This analysis was conducted within a prospective pregnancy cohort study. The study population included 187 women. 2D:4D was measured directly in both hands using a digital caliper. Multivariable linear and logistic models were used to study the associations between digit ratio and the studied health characteristics. Mean age of the participants was 30.7 ± 4.9 years. The mean age at menarche was 12.9 ± 1.4 years. Right hand 2D:4D mean ± SD was 0.965 ± 0.03. Left hand 2D:4D mean ± SD was 0.956 ± 0.03. An association was found between right 2D:4D and age at menarche, with older age in women with 2D:4D ≥ mean versus 2D:4D < mean (13.2 ± 1.5 and 12.8 ± 1.3 respectively, b = 0.48, 95%CI:0.06–0.91) while controlling for ethnicity. Higher 2D:4D was also associated with heavier menses bleeding and dysmenorrhea. There is an association between 2D:4D and sub optimal reproductive characteristics, including later age at menarche, heavier menses bleeding and dysmenorrhea. These findings support the association between the intrauterine period and reproductive characteristics. Further studies are required to support our findings.

Low digit ratio (2D:4D) is associated with early natural menopause

Objectives

Intrauterine environmental conditions may affect the number of primordial follicles and in this way the timing of menopause. The aim of the present study was to investigate association patterns between right hand digit ratio, that is, 2D:4D ‐ as an indicator of prenatal androgen and estrogen exposure, and age at menopause.

Methods

One hundred sixty‐nine women, who had experienced natural menopause, were enrolled in the study. Length of second and fourth finger were measured directly from the palmar side and digit ratios of both hands were calculated. For further analyses the digit ratio of the right hand was used only. Additionally, smoking habits, body weight and body height, body mass index and the number of children were determined. Multiple regression analyses were used to test association patterns between digit ratio and age at menopause, body height, BMI, nicotine consumption as well as number of births and age at menopause.

Results

Age at menopause correlated significantly positively with the digit ratio. A more feminine digit ratio is associated with a higher age at menopause, while a low digit ratio, interpreted as a hint of a higher androgen exposure during prenatal phase was associated with a lower age at menopause.

Conclusions

Low digit ratio is associated with an earlier onset of natural menopause.

The associations between left-hand digit ratio (2D:4D) and puberty characteristics among Chinese girls

BACKGROUND

The aim of this study was to analyse the associations of left-hand digit ratio (2D:4D), digit length and puberty characteristics to show the role of prenatal hormones in development among Chinese girls.

METHOD

A total of 318 Chinese girls aged 8-15 years were recruited using a stratified cluster sampling method. The index finger (2D), ring finger (4D) of the left hand, oestradiol and testosterone were measured, and age at menarche (AAM), breast (high and low) and pubic hair (high and low) development were recorded.

RESULTS

Girls who had experienced menarche had longer left digits (2D and 4D) and higher oestradiol, testosterone than those who had not. The high breast group had longer digits (2D and 4D), and higher oestradiol than the low breast group. With regard to pubic hair development, the high group had high 2D:4D, longer 2D and higher oestradiol, testosterone than the low group. After adjusting for oestradiol and testosterone, 4D length was positively related to occurrence of menarche. In addition, 2D and 2D:4D were significantly correlated with pubic hair development after adjusting for oestradiol, respectively.

CONCLUSION

Prenatal hormone level may be related to the development of puberty characteristics among Chinese girls.

Age of pubertal onset and 2nd to 4th digit ratios: Preliminary findings

BACKGROUND

The second to fourth digit ratio (2D:4D) is used as a marker of prenatal sex hormone exposure. The aim of this study was to evaluate the possible relation between digit ratio and age of pubertal onset.

METHODS

Participants were 321 men and 202 women aged between 18 and 28 at the time of assessment who self-reported their onset of puberty (i.e., age at first conscious ejaculation or menarche). Participants' right and left digit lengths were measured from hand scans.

RESULTS

All groups of males, i.e., early, average, and late pubertal onset, had lower mean 2D:4D than the comparable female groups, regardless of the relative timing of their pubertal onset. Among the males, there was a significant difference in digit ratios between individuals who experienced early, average, and late onset of puberty. In the males, we observed a positive relationship between 2D:4D and age of pubertal onset for both right and left hands. There were no significant differences in 2D:4D among the three groups of female maturers. We observed no significant association between digit ratios and age at menarche.

CONCLUSIONS

These data lend further support for using 2D:4D as a measure of prenatal androgen exposure.

Stability of proposed biomarkers of prenatal androgen exposure over the menstrual cycle

The prenatal hormonal milieu is widely believed to shape health later in life; however, there are considerable methodological challenges associated with measuring the in utero hormonal environment. Two potential biomarkers of prenatal androgen exposure that can be measured postnatally have been proposed: anogenital distance (AGD) and the ratio of the second to fourth digits of the hand (2D:4D). Although both measures are widely used research tools, their use in adult women may be complicated by the dramatic fluctuations in reproductive hormones across the menstrual cycle. To determine whether there is cyclical variation in these biomarkers, we conducted a longitudinal study of 12 naturally cycling, nulliparous adult women. Trained examiners assessed two measures of AGD [anus to clitoris (AGD-AC) and anus to fourchette (AGD-AF)] and 2D:4D in both hands for the duration of three menstrual cycles, taking measurements during the follicular, peri-ovulatory and luteal phases of each cycle. Despite the small sample size, longer (more masculine) AGD was associated with lower (more masculine) digit ratios, as predicted by the literature. Using multi-level linear regression models, we found that AGD and 2D:4D measurements did not differ significantly across cycle phases. AGD-AF and digit ratios in both hands were associated with age at menarche, suggesting a possible common developmental trajectory. These results demonstrate that AGD and 2D:4D are stable across the menstrual cycle. In addition, research is needed to determine how reliably these measures reflect the in utero hormonal milieu.

Digit ratio (2D:4D) and competition level in world-class female gymnasts

In this study the relationship between the digit ratio (2D:4D) and artistic gymnastics performance and competition level was investigated in a sample of Caucasian world-class female gymnasts (n = 145). The sample was divided into three competition events (compulsories, free work, final score). Within each event three performance groups (lowest, middle, and highest) were based on the competition scores gathered at the World Championships at Rotterdam, the Netherlands, in 1987. Lengths of the digits were measured on X-rays of the left hand. Several anthropometric dimensions were measured and from those measurements an androgyny index (Bayer & Bayley) and somatotype components (endomorphy, mesomorphy, ectomorphy) were calculated. Although significant differences in some anthropometric characteristics between the performance level groups within each competition event were observed, no significant differences in the 2D:4D ratios were found between the performance level groups, varying from 0.918 ± 0.020 to 0.924 ± 0.020. Also, no significant correlations were observed between the 2D:4D ratio and anthropometric, androgyny, and somatotype characteristics, r varying from r = -0.11 to r = +0.12. It can be concluded that in this sample the 2D:4D digit ratio, unlike other anthropometric characteristics, is not a discriminating factor for the performance in artistic gymnastics performance on a world-class level.

Low digit ratio predicts early age at menarche in Colombian schoolgirls

BACKGROUND

The ratio between the lengths of the second and fourth fingers (digit ratio: 2D : 4D), a purported negative correlate of prenatal androgen exposure, has been inversely related to age at menarche. However, a recent study found high digit ratios in carriers of a single variant in the LIN28B gene, which has been linked to delayed menarche.

METHODS

We investigated the association of digit ratio and age at menarche in 299 pre-menarcheal girls aged 5-12 years who participated in a longitudinal cohort study in Bogotá, Colombia. Finger lengths were measured at baseline and the occurrence of menarche was periodically ascertained over a median 32 months of follow-up. We used time-to-event analysis to estimate median ages at menarche as well as hazard ratios for menarche according to tertiles of the digit ratio for each hand.

RESULTS

Estimated median age at menarche was lower for girls in the lowest digit ratio tertile of the right hand compared with those in the highest (12.0 vs. 12.3 years; P-value = 0.04). After adjustment for baseline age, height- and body mass index-for-age z-scores, the hazard of menarche was 86% higher in girls of the lowest digit ratio tertile (hazard ratio 1.9 [95% confidence interval 1.2, 2.9]) compared with those in the highest digit ratio tertile of the right hand. No significant associations were found with the left hand.

CONCLUSIONS

Digit ratio was positively associated with age at menarche in this longitudinal investigation, consistent with results from a recent gene-linkage study.

The left hand second to fourth digit ratio (2D:4D) does not discriminate world-class female gymnasts from age matched sedentary girls

Introduction

The second to fourth-digit-ratio (2D:4D), a putative marker of prenatal androgen action and a sexually dimorphic trait, has been suggested to be related with sports performance, although results are not univocal. If this relation exists, it is most likely to be detected by comparing extreme groups on the continuum of sports performance.

Methods

In this study the 2D:4D ratio of world-class elite female artistic gymnasts (n = 129), competing at the 1987 Rotterdam World-Championships was compared to the 2D:4D ratio of sedentary age-matched sedentary girls (n = 129), alongside with other anthropometric characteristics including other sexually dimorphic traits such as an androgyny index (Bayer & Bayley) and Heath-Carter somatotype components (endomorphy, mesomorphy, ectomorphy) using AN(C)OVA. 2D:4D was measured on X-rays of the left hand.

Results

Left hand 2D:4D digit ratio in world class elite female gymnasts (0.921±0.020) did not differ significantly from 2D:4D in age-matched sedentary girls (0.924±0.018), either with or without inclusion of potentially confounding covariates such as skeletal age, height, weight, somatotype components or androgyny index. Height (161.9±6.4 cm vs 155.4±6.6 cm p<0.01), weight (53.9±7.6 kg vs 46.2 6.3 kg p<0.01), BMI (20.51±2.41 kg/m² vs 19.05±1.56 kg/m²), skeletal age (15.2±1.1 y vs 14.5±1.2 y p>0.01), somatotype components (4.0/3.0/2.9 vs 1.7/3.7/3.2 for endomorphy (p<0.01), mesomorphy (p<0.01) and ectomorphy (p<0.05) respectively) all differed significantly between sedentary girls and elite gymnasts. As expressed by the androgyny index, gymnasts have, on average, broader shoulders relative to their hips, compared to the reference sample. Correlations between the 2D:4D ratio and chronological age, skeletal age, and the anthropometric characteristics are low and not significant.

Conclusion

Although other anthropometric characteristics of sexual dimorphism were significantly different between the two samples, the present study cannot discriminate sedentary girls from world-class female gymnasts by means of the left hand 2D:4D ratio.

Is low digit ratio linked with late menarche? Evidence from the BBC internet study

OBJECTIVES

Age at menarche (AAM) in the general population may be influenced by prenatal sex steroids. The ratio of the second and fourth digits (2D:4D) is a putative correlate of prenatal sex steroids, but the relationship of 2D:4D to AAM is controversial. Matchock ([2008]: Am J Hum Biol 20:487-489) has reported that right 2D:4D (but not left) was negatively related to AAM, but Helle ([2010a]: Am J Hum Biol 22:418-420) found no relationship. Here the association between 2D:4D, AAM, and self-reported rate of pubertal development (RPD) is considered.

METHODS

The sample consisted of self-measured finger lengths and AAM and RPD reported by women in the BBC internet study.

RESULTS

There were 70,658 white women who reported a mean (± SD) AAM of 12.54 (1.48) years. Right 2D:4D was negatively related to AAM and positively related to RPD. These relationships were independent of left 2D:4D, age and height. Between-country variation in right 2D:4D was also significantly related to AAM such that in countries with low 2D:4D women mean AAM was higher.

CONCLUSIONS

In support of the findings of Matchock, right 2D:4D was found to be negatively related to AAM. In addition, right 2D:4D was positively related to RPD. In a sample of 19 countries, mean right 2D:4D was negatively correlated with mean national AAM. These findings suggest that women with high prenatal testosterone and low prenatal estrogen tend to show late menarche and slow pubertal development.