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Pituitary-Gonadal Function in Adolescent Males Born Appropriate or Small for Gestational Age with or without Intrauterine Growth Restriction

University Department of Growth and Reproduction (R.B.J., A.J.), and University Department of Neonatology (S.V., G.G.), Rigshospitalet, DK-2100 Copenhagen, Denmark; Department of Gynaecology and Obstetrics (T.L.), Holbaek Sygehus, Sygehus Vestsjaelland, DK-4300 Holbaek, Denmark; and Division of Endocrinology and Metabolism (J.V.), Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota 55905

Address all correspondence and requests for reprints to: Rikke Beck Jensen, M.D., University Department of Growth and Reproduction, Rigshospitalet, Section 5064, Blegdamsvej 9, DK-2100 Copenhagen Ø, Denmark. E-mail: rikke.beck{at}dadlnet.dk.

	Abstract

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Context: Being born small for gestational age (SGA) is suggested to influence female pituitary-gonadal axis, but only a few studies have focused on male pituitary-gonadal function.

Objective: Our objective was to evaluate the influence of fetal growth rate on male reproductive function.

Design: We conducted a follow-up study of a prospective study with data on third trimester fetal growth velocity and birth weight.

Setting: The study was conducted at Copenhagen University Hospital.

Participants: Fifty-two healthy adolescent males participated. They were divided into those born appropriate for gestational age (AGA) and SGA, with or without intrauterine growth restriction.

Main Outcome Measures: Pubertal stage, testicular size, and reproductive hormones were determined. Overnight 20-min LH and FSH profiles and overnight urine LH and FSH were determined in an additional study (n = 30).

Results: No significant differences were found in testosterone levels (19.2 vs. 18.9 nmol/liter), inhibin B levels (186.5 vs. 188.0 pg/ml), or LH/testosterone ratio (0.15 vs. 0.18) between AGA and SGA, respectively. No significant differences in overnight secretory patterns of gonadotropins or testicular size and morphology were determined by ultrasonography between AGA and SGA. Fetal growth velocity did not influence any of the reproductive hormone levels. Overnight urinary LH and FSH excretion correlated statistically significantly with overnight LH (r = 0.50; P = 0.02) and FSH (r = 0.44; P = 0.04) secretion, respectively.

Conclusion: Poor third trimester growth and/or low birth weight had no effect on subsequent male reproductive hormones. Contrasting a previous study, we found no difference in testosterone or inhibin B levels between SGA and AGA, suggesting that testicular function was not impaired in adolescent males born after compromised fetal growth.

	Introduction

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LOW BIRTH WEIGHT as a consequence of intrauterine growth restriction (IUGR) is associated with increased risk of perinatal morbidity and mortality, and an increased risk of disease in adult life (1). A suboptimal intrauterine environment may have a detrimental effect on gonadal development and thereby increase the risk of cryptorchidism and hypospadias in the newborn (2), and furthermore increase the risk for poor semen quality and testicular cancer in adult life (3, 4). The entity of cryptorchidism, hypospadias, poor semen quality, and testicular cancer has been termed the testicular dysgenesis syndrome (5), which proposes a common fetal origin of these conditions. Being born small for gestational age (SGA) is a result of IUGR during variable periods of gestation. Growth restriction may occur due to a chromosomal disorder or alternatively due to maternal restraint caused by either environmental factors or a genetically determined decreased growth rate. No studies have evaluated the influence of intrauterine growth rate on adult reproductive function.

We hypothesized that low birth weight corrected for gestational age and/or IUGR in third trimester of pregnancy may determine the function of the adult pituitary-gonadal axis.

	Subjects and Methods

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Fifty-two healthy men aged 16–18 yr participated in a follow-up study. Their mothers were included in a randomized controlled trial on fetal growth performed in 1985–1987, including pregnant women with risk factors for giving birth to an SGA child (6). Serial ultrasound measurements in the third trimester allowed calculation of fetal growth velocity (FGV; expressed as changes in estimated fetal weight per 28 d). IUGR in the third trimester was defined as growth velocity below the 10th percentile of a normal fetal growth curve [–0.39 SD score (SDS) per 28 d] (7) (Fig. 1). Furthermore, the cohort was divided into infants born with a birth weight appropriate for gestational age (AGA) or SGA (below the 10th percentile or –1.28 SDS) (7). In the follow-up study performed in 2003–2005, a sample of 128 males was invited, and 52 of these males participated (participation rate of 41%). Thirty-two participants were born AGA (eight with IUGR), and 20 were born SGA (seven with IUGR). There were no significant differences in birth weight (–0.63 vs. –0.61 SDS) or in third trimester FGV (–0.17 vs. –0.19 SDS per 28 d) between participants and nonparticipants, respectively. An additional study on pituitary-gonadal function was performed in which all 52 male participants were invited and 30 agreed to participate (participation rate of 58%). There was no significant difference in basal reproductive hormones in the original group and those participating in the additional study.

View larger version (51K): [in this window] [in a new window]   FIG. 1. Top, Individual intrauterine growth curves (n = 30), including actual birth weight measurements. Bold lines represent the 10th, 50th, and 90th percentiles of a normal fetal growth curve. Middle, LH overnight secretion for each individual based on 20-min blood sampling interval. Bottom, FSH overnight secretion for each individual. The participants were divided into those born AGA and those born SGA.

The study was performed according to the Helsinki II declaration and approved by the local Ethical Committee. Written informed consent was obtained from all participants or from the parents/guardians.

Study design

The participants arrived fasting in the morning, and blood samples were drawn. Height (centimeters) was measured using a stadiometer, and weight (kilograms) was measured on a digital weight scale. The SDS for height and weight were calculated based on a national reference (8). Pubertal stage and testicular size were determined. Testicular size and morphology were determined by ultrasound (9). Pulsatile hormone assessments (n = 30) were carried out during overnight admission where blood samples were collected at 20-min intervals from 2000 to 0800 h. Participants collected urine overnight (12 h).

Biochemical assays

Male reproductive hormones were determined in the morning blood sample. Blood samples were centrifuged, and serum was stored at –20 C until analysis. Assays included: testosterone by time-resolved fluoroimmunoassay (DELFIA; Wallac, Turku, Finland), detection limit 0.23 nmol/liter, and intra- and interassay coefficient of variation (CV) less than 6%; estradiol by RIA (Pantex Corp., Santa Monica, CA), detection limit 18 pmol/liter, intraassay CV less than 8%, interassay CV less than 13%; inhibin B by specific two-sided enzyme immunometric assay from Oxford Bio-Innovation Ltd. (Oxford, UK), sensitivity 18 pg/ml, and intra- and interassay CV less than 12 and 17%, respectively; SHBG by time-resolved immunofluorometric assay (DELFIA; Wallac, Inc.), detection limit 0.23 nmol/liter, intra- and interassay CV less than 5.1%. Free testosterone concentration was calculated using the equation of Vermeulen et al. (10). FSH and LH concentrations were measured by time-resolved immunofluorometric assay (DELFIA; Wallac, Inc.), detection limits 0.06 and 0.05 U/liter, respectively; and intraassay and interassay CV less than 5%.

Urinary LH and FSH

Urine samples (2 ml) were supplemented with 80 µl BSA (25% BSA stock) and 150 µl glycerol and were stored at –20 C until analysis. Urinary LH and urinary FSH concentrations were measured by Delfia immunofluorometric assays (Wallac) (11).

Analysis of pulsatile hormone secretion

A two-component deconvolution analysis was applied to estimate pulsatile LH and FSH secretion in each individual from the overnight profiles, using techniques described previously by Veldhuis and Johnson (12). Preliminary fits of the data were made by a waveform-independent deconvolution methodology (PULSE2) followed by a multiparameter deconvolution methodology. Fixed rapid-phase half-lives and fitted slow-phase half-lives for LH and FSH were used (13, 14). Approximate entropy (ApEn) analysis was calculated (15). ApEn parameters of m = 1 and an r value of 0.35 (35%) of the SD of the individual subject time series were chosen. Higher absolute ApEn denotes greater disorderliness of hormone release, and vice versa, for lower ApEn.

Statistical analysis

The majority of the variables compared were nonnormal distributed; thus the results are provided as median and interquartile range (IQR) and compared by Mann-Whitney U test (level of significance < 0.05). However, the strategic sampling of the study resulted in a skewed distribution of FGV and birth weight (BW) SDS toward lower values, and to counter for this bias a weighting of the underrepresented group in a univariate linear regression analysis was performed. Furthermore, bootstrapped SE of estimates was applied for the calculation of confidence intervals of the weighted estimates. In the univariate or multivariate (general linear model) regression analyses, the nonnormal distributed dependent variables were transformed to normality before being entered into the model. Because no statistically significant differences were apparent in the regression model, the raw data divided according to BW status (AGA vs. SGA) were presented for the purpose of clarification. The statistical analyses were carried out using the statistical package SPSS (version 14.0; SPSS, Inc., Chicago, IL).

	Results

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Median age for the 52 adolescents included in this study was 17.2 yr (IQR, 16.6–17.9). Median height was 177.8 cm (IQR, 173.0–182.8), equal to +0.1 SDS, and median weight was 66.1 kg (IQR, 59.9–76.0), equal to +0.46 SDS. Significantly reduced height SDS was seen in men born SGA (median, –0.53 vs. 0.47 SDS; P = 0.003) (Table 1). Measurements of basal reproductive hormones showed no statistically significant differences in the group born SGA compared with those born AGA (Table 1). Univariate weighted linear regression analysis showed no independent effect of BW or FGV on the basal reproductive hormones. Ultrasound scan of testes showed no significant difference in testicular size or morphology between those born SGA and AGA (n = 30). Deconvolution analyses revealed no significant differences in the overnight LH and FSH secretory patterns in the groups born AGA and SGA, respectively (Table 1). Median basal LH secretory rates were 2-fold higher in men born AGA [15.1 (IQR, 6.8–24.5) vs. 7.1 (IQR, 4.5–12.1) IU/liter·12 h], but the difference did not reach statistical significance (P = 0.24). Multivariate linear regression analysis with deconvolution results as dependent variables and BW SDS, FGV, and age as independent variables showed no association between LH and FSH secretory patterns and either BW SDS or FGV (data not shown). The ApEn values as an estimate of the orderliness of the hormone secretion revealed no significant difference for either LH or FSH, and the ApEn ratios indicated well-ordered (strongly non-random) behavior.

	Discussion

Top Abstract Introduction Subjects and Methods Results Discussion References

 
In this detailed clinical study on the influence of birth weight and fetal growth rate on the pituitary-testicular axis in adolescent males, assessed by basal reproductive hormones and overnight 20-min FSH and LH profiles, we found no significant differences in basal reproductive hormones or in the secretory pattern of gonadotropins between the adolescents born AGA and SGA. There were no differences in testicular volume and ultrasonographic morphology between those born AGA and SGA. Our present findings contrast the only existing study on this topic (16). Importantly, third trimester fetal growth rate per se did not have an independent effect on gonadal function in adolescence. To our knowledge, this is the first study to explore the influence of third trimester fetal growth rate on subsequent adult gonadal function.

The majority of studies exploring the association between low birth weight and pituitary-gonadal axis have focused on female reproductive function. Such studies have suggested that young women born SGA have decreased ovarian hormones (17), reduced ovarian volume, and an increased number of anovulatory cycles (18). For boys there is evidence that low birth weight corrected for gestational age is associated with increased risk of cryptorchidism and hypospadias (2, 19), and furthermore decreased fertility as well as an increased risk of testicular cancer in adult life. The association between SGA and male reproductive hormones has only been evaluated in one former clinical study in which significantly decreased testosterone and elevated LH levels were found in 25 men born SGA (BW < 10th percentile) compared with 24 men born AGA (16). These findings may suggest a primary testicular failure in men born SGA; however, five of the SGA individuals had cryptorchidism at birth, and the control group consisted of 20 patients with constitutional short stature (16). In our similar sized study, it was not possible to detect a statistically significant effect of poor intrauterine growth and/or low birth weight on subsequent male reproductive hormones. In our study, there were no differences in testosterone and inhibin B levels between the two groups, suggesting that low birth weight per se does not influence testicular function. However, genital malformations (like cryptorchidism) associated with SGA may have an effect on subsequent gonadal function.

Our participants were recruited from a large prospective study in which 1000 pregnant women were included consecutively; thus the group may be less selected compared with the group studied by Cicognani et al. (16). Importantly, we found no statistical differences in BW or FGV between the 52 participants and the 74 subjects who declined to participate (nonparticipants). Furthermore, there were no significant differences in basal reproductive hormones or any of the clinical characteristics between the participants with an overnight hormone profile and those who declined. Thus, we do not believe our study is influenced by major selection bias, although this cannot be entirely excluded.

In conclusion, smallness at birth was not associated with adolescent male pituitary-testicular function and, importantly, fetal growth rate in third trimester per se did not influence the outcomes. Further studies are needed to clarify if being born SGA subtly influences male pituitary-gonadal function, as it has been suggested for women born SGA.

	Footnotes

 
Disclosure Statement: R.B.J., S.V., and G.G. received financial support for the project from Novo Nordisk A/S. T.L., J.V., and A.J. have nothing to declare.

First Published Online January 16, 2007

Abbreviations: AGA, Appropriate for gestational age; ApEn, approximate entropy; BW, birth weight; CV, coefficient of variation; FGV, fetal growth velocity; IQR, interquartile range; IUGR, intrauterine growth restriction; SDS, SD score; SGA, small for gestational age.

Received October 26, 2006.

Accepted January 4, 2007.

	References

Top Abstract Introduction Subjects and Methods Results Discussion References

 

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