Table 1 Main features of RCTs and observational studies assessing timing for CF introduction in preterm infants

Baldassarre, 2018 [19]

Observational study

Survey of CF practices among 347 Italian primary care paediatricians

Wide heterogeneity in CF timing (based on age or neurodevelopmental skills or body weight), quality, and prescription of vitamin D and iron supplements.

Marriott, 2003 [61]

RCT

 RCT comparing PWS vs. conventional CF management in 68 preterm infants randomised to either the PWS group (n = 37) or control group (n = 31)

Infants in the PWS group showed higher length scores and length growth velocity, and higher intake of energy, carbohydrate, protein, and iron during follow up.

Spiegler, 2015 [35]

Observational study

Longitudinal analysis of introduction of CF in 981 German VLBW infants, risk factors for early introduction of CF, and relationship between age at CF start and growth at 2 years of age

Average introduction of CF was 3.5 months CA. Lower GA correlated with earlier introduction of vegetables and meat. Age at introduction of CF was influenced by IUGR, GA at birth, maternal education and a developmental delay perceived by parents. No negative effect of early introduction of CF on length and weight at 2 years of age.

Rodriguez, 2018 [46]

Observational pilot study

Cross-sectional study assessing the relationship between feeding practices and weight gain at 18–24 months CA in 36 toddlers born < 32 weeks’ GA

Forty-one % infants received CF before four months CA. A greater weight gain was observed in infants on early CF.

Gupta, 2017 [62]

RCT

RCT comparing CF starting at 4 vs. 6 months CA in 373 Indian preterm infants born < 34 weeks’ GA (n = 184 CF at 4 months CA vs. n = 189 CF at 6 months CA)

No difference was found in weight-for-age z score at 12 months CA between groups, but a higher hospitalization rate was documented in the 4 month CF group.

Morgan, 2004 [21]

Pooled RCTs results

Pooled results from 5 RCTs assessing early (< 12 weeks) vs. late (> 12 weeks) introduction of CF in 1694 term and preterm infants

Preterm infants weaned before 12 weeks featured slower increase in weight, length, and head circumference at 12 weeks − 18 months; by 18 months, there were no significant differences in size between the two groups.

Zielinska, 2019 [54]

Observational study

Cross-sectional study investigating n = 5815 parents of infants aged 1–3 years from Poland (n = 4065) and Austria (n = 1750) using a single online questionnaire

Cross-sectional study assessing risk factors for early CF in Poland and Austria.Preterm birth was a significant risk factors for early CF, together with lower maternal age and educational level, absence of breastfeeding and formula feeding after hospital discharge.

Cleary, 2020 [55]

Observational study

Prospective longitudinal study on 150 infants (preterm n = 85; term n = 65)

Structured interviews on infant feeding practices, growth and medical status in term and preterm infants. Preterm infants received CF earlier than term infants; lower maternal education and male gender were significant risk factors for early CF.

Fanaro, 2007 [56]

Observational study

Survey of CF practices in an Italian region on n = 156 infants

Significant variation in timing and inappropriate equality of CF (low energy, protein, iron and zinc content). Maternal age significantly influenced the weaning schedule.

Norris, 2002 [57]

Observational study

Two-hundred and fifty-three preterm infants (139 male, 114 female) assessed by structured interviews in the UK

Nearly half of the sample received early CF. Formula-fed infants (mean age at CF from term 10.2 ± 0.47 weeks) were weaned significantly earlier than both human milk-fed (11.9 ± 0.49 weeks; p < 0.05) and combined milk-fed (11.9 ± 0.25 weeks; p < 0.005) infants.

Braid, 2015 [58]

Observational study

Multivariate logistic regression on 7650 infants (term vs. preterm)

Higher odds of early CF in ELGAN. Lower GA was associated with higher odds of early CF.

Giannì, 2018 [59]

Observational study

Assessment of CF practices in a cohort of 64 Italian late preterm infants

Late preterm infants started CF at almost six months of age receiving first solid foods with low energy and protein content.

Menezes, 2018 [60]

Observational study

Cross-sectional study on 38 preterm infants to investigate difficulties in CF in premature infants

Nearly 75% of preterm infants experienced at least one defensive behaviour at mealtime (e.g., refusal to open their mouth, food selectivity, and feeding refusal).

Crapnell, 2013 [36]

Observational study

Assessment of early medical and family factors associated with later CF in 136 preterm infants (≤30 weeks’ GA)

Nearly a quarter of infants experienced feeding problems at 2 years. Early hypotonia and lower socio-economic status were documented as risk factors for delayed CF.