Body composition and physical fitness in adults born small for gestational age at term: a prospective cohort study

Examine style and design

This examine is a component of the NTNU Reduced Start Weight in a Lifetime Standpoint review. The current study involved two teams of adults born in 1986–1988 one particular team born SGA at term, and a person team born non-SGA at expression with start weight ≥ 10th percentile, which serves as a handle group. The participants took portion in a bigger info selection at 32 years of age. In addition to physical exercise assessments, exams involved anthropometric measurements, evaluation of lung perform, visual purpose as nicely as good and gross motor functionality. Assessments were being carried out from September 2019 to Oct 2020.


Members have been in the beginning included in a multicentre analyze investigating the aetiology and penalties of intrauterine development restriction29,30. Expecting women dwelling in the Trondheim location have been enrolled prior to 7 days 20 of being pregnant based mostly on referral from general practitioners and obstetricians. Ladies were eligible if they had a singleton being pregnant and experienced been pregnant just one or two situations before (n = 1249). A 10{fc1509ea675b3874d16a3203a98b9a1bd8da61315181db431b4a7ea1394b614e} random sample of these gals were picked to serve as a management group (n = 132), applying a sealed envelope technique. A group of females at significant possibility of offering start to an SGA infant have been selected for abide by-up if they had a single or additional defined chance standards for SGA delivery a past low start bodyweight kid, minimal pre-being pregnant fat (< 50 kg), previous perinatal death, presence of chronic maternal disease (chronic renal disease, essential hypertension, or heart disease), or maternal cigarette smoking at conception (n = 390). Women in the control group and the high-risk group were thoroughly followed during pregnancy and their infants were examined at birth. The rest of the women (n = 727) were not followed during pregnancy (Fig. 1).

Figure 1
figure 1

Flow of participants. SGA small for gestational age.

At birth, all SGA infants born to mothers in either group were included in the SGA group (Fig. 1). An infant was defined as being born SGA if the birth weight was < 10th percentile for gestational age (GA), corrected for sex and parity, according to a reference standard using data from the Norwegian Medical Birth Registry29. Non-SGA infants born to mothers in the random sample were included in the control group. They were born with a birth weight ≥ 10th percentile. GA was based on the first day of the mother’s last menstrual period if this was accurately recalled ± 3 days. Ultrasound based GA was used if the last menstrual period was not recalled, or if there was a discrepancy of more than 14 days. Both groups were born at term (GA ≥ 37 weeks)29,30.

The total sample included 104 participants born SGA and 120 controls (Fig. 1). Three individuals born SGA and two controls were excluded due to death, congenital syndrome/anomaly, or multimorbidity. Of the eligible, 15 individuals born SGA and 14 controls were not invited because they were living abroad, had no contact information or had previously refused to participate. Thus, a total of 190 were invited to the present study, 86 in the SGA group and 104 in the control group. Of these, 30 individuals born SGA and 36 controls did not consent to participate. Furthermore, 10 individuals born SGA and seven controls were not assessed clinically. Thus, 46 participants born SGA and 61 controls were assessed clinically, corresponding to 56.3{fc1509ea675b3874d16a3203a98b9a1bd8da61315181db431b4a7ea1394b614e} of the invited.


There were no significant differences between participants and those who did not consent or were not assessed clinically regarding sex, gestational age, birth weight, head circumference, body length, ponderal index, maternal age at child’s birth or parental socioeconomic status (SES) in either group (data not shown). From the 26-year follow-up data were available on height, weight, BMI, waist and hip circumference, skinfold thickness and body composition measured by dual-energy x-ray absorptiometry (DXA). In the SGA group there were no differences, but in the control group, participants weighed 8.9 (95{fc1509ea675b3874d16a3203a98b9a1bd8da61315181db431b4a7ea1394b614e} CI 1.0 to 16.8) kg less than those who did not consent or were not assessed clinically.

Background characteristics

At birth, the infants in both groups were weighed to the nearest 10 g on a standard scale, and crown-heel length was measured with both legs extended to the nearest mm30. Ponderal index (g/cm3) was calculated based on these measurements.

Parental socioeconomic status (SES) was calculated when participants attended the 14-year follow-up, supplemented for two participants at the 19-year follow-up, according to Hollingshead’s Two Factor Index of Social Position31, based on the parents’ education and occupation. This gives a social class rating from 1 (lowest) to 5 (highest).

Educational attainment at the 32-year follow-up was collected by self-report and classified according to the International Standard Classification of Education (ISCED) levels 1 through 8. These were recoded into three categories: Lower secondary education or lower (ISCED levels 1–2) as no more than 10th class level, intermediate education (ISCED levels 3–5) as 11th–14th class level, and lower tertiary education or higher (ISCED levels 6–8) as a bachelor’s degree or higher.

Outcome measures

Assessments were carried out at NTNU/St. Olavs Hospital in Trondheim, Norway. A brief medical interview was conducted prior to examination, including whether the participant was pregnant, had a musculoskeletal diagnosis or other conditions affecting physical functioning. If the participant had a condition that made them unable to perform a physical test or that could be worsened by testing, they did not perform that particular test. All examinations were carried out by experienced and specially trained examiners, blinded to birth weight group. Anthropometric measurements were performed by a nurse and physical fitness tests by two physiotherapists and a medical research student. The examinations were carried out in the same order for each participant.

At follow-up, the participants’ height, waist and hip circumference were measured to the nearest mm. Waist circumference was measured at the mid-point between the lowest rib and the crista iliaca, and hip circumference at the maximal circumference over the buttocks. Weight was measured by bioelectric impedance analysis using a Seca medical Body Composition Analyzer (Seca® mBCA 515) with a 100 g accuracy. Body mass index (BMI, kg/m2) and waist-to-hip ratio (waist circumference/hip circumference) was calculated. Bioelectrical impedance analysis measures included percent body fat, fat mass, fat free mass, skeletal muscle mass, total body water and extracellular water using the Seca 115 analytics software (Seca GmbH, Hamburg, Germany).

Muscular fitness was measured by the maximal isometric grip strength of the hands and forearm muscles. A Jamar (Smith and Nephew, Memphis, TN) hand dynamometer was used. The dynamometer has 5 handle positions position 3 and 4 were used for women and men, respectively. The participants were seated during the test, with shoulder abducted, a 90° angle in the elbow and a neutral position in the wrist, without support of the forearm32. Measurement was repeated three times in both dominant and non-dominant hand with 30 s recovery in between each attempt. Grip strength was measured in kg force and the maximal grip strength of the three measurements for each hand was used in the analysis. One participant in the control group could not perform the grip strength test with the dominant hand due to a hand fracture.

The 40-s modified push-up test measures the muscular strength and endurance capacity of the upper body33 and is modified to improve standardisation. The participants started laying prone on a mat with their hands close to the shoulders and feet hip-width apart with their toes on the mat33. Before every push-up they had to clasp hands behind their back before pushing themselves to a straight leg push-up. In the top position they had to touch either of their hands with the other hand before returning to the push-up position and returning to the down-position. The number of correctly performed push-ups in 40 s were registered. One participant in the control group could not perform the push-up test due to a hand fracture.

The Åstrand-Ryhming step test is a 4-min submaximal step-test that measures cardiorespiratory fitness34. The participants stepped on and off the step for four minutes paced by a metronome set to 46 beats per minute (i.e., 23 times up on the step/min). The height of the step was adapted to sex: 33 cm for women and 40 cm for men. Heart rate was observed during the test using a heart rate monitor (Firstbeat Technologies Oy) and recorded after 4 min of stepping and after being seated for 2 min. Two participants born SGA were not able to complete the test and were excluded from the analysis.

Statistical analysis

The analyses were conducted in SPSS version 27 (IBM Statistics). A p-value of less than 0.05 was considered statistically significant. Background characteristics were examined using Student’s t-test for continuous data, Exact Mann–Whitney U test for ordinal data and Pearson’s Chi square test for dichotomous variables. Group differences in outcome measures were analysed using independent samples t-test. The assumption of normally distributed variables was checked by visual inspection of histogram, boxplot, and Q–Q-plots of standardised residuals. As physical fitness differs between women and men35,36, we performed separate analyses by sex. Differences in physical fitness between groups were adjusted for height as a potential mediating factor in a univariate general linear model, since height has been consistently correlated with both being born SGA4,12,37 and physical fitness in previous literature22.

To investigate whether physical conditions affected the results, sensitivity analyses were performed by excluding participants who were pregnant, had a musculoskeletal diagnosis or other conditions affecting physical functioning, as reported by the participants in the brief medical interview.

A priori power calculations suggested, based on previous follow-up numbers in the SGA (n = 64) and control group (n = 81)38, that we would have the power to detect differences of 0.48 SD units with an alpha-level of 0.05 and a power of 80{fc1509ea675b3874d16a3203a98b9a1bd8da61315181db431b4a7ea1394b614e}, and 0.67 SD units with an alpha-level of 0.01 and desired power of 90{fc1509ea675b3874d16a3203a98b9a1bd8da61315181db431b4a7ea1394b614e}.


The study was approved by the Regional Committee for Medical and Health Research Ethics in Central Norway (23879). Written informed consent was obtained from all participants. All methods were performed in accordance with the relevant guidelines and regulations. The data was pseudonymised and stored securely on a remote server with a two-step identifier. All methods were non-invasive and entailed low risk for injury or adverse events. An appointed doctor was medically responsible during data collection. Participants in need of health services were referred as appropriate.