A total of 988 preterm infants have been involved in this study, and their data for the first year of their lives were evaluated and analyzed. Among a total of 988 subjects, at least in 725 (73.4%), a single FGID was documented with the first of life. There are 484 (49.0%) cases with a single kind of FGIDs, 210 (21.3%) with two kinds, 31 (3.1%) with three kinds, and no case with four or more FGIDs found. Among the 988 participants, there were 449 (45.4%) and 411 (41.6%) cases of infant colic and regurgitation, respectively, making them frequently occurring disorders. Of the 988 participants, 237 (24.0%) claimed dyschezia, 190 (19.2%) claimed functional constipation, and 34 (3.4%) claimed functional diarrhea. There were no cases of infant rumination syndrome as well as recurrent vomiting syndrome.
The demographic characteristics of subjects are shown in Table 1. Of the 988 infants who completed the study, 725 with FGIDs were allotted to the case group and 263 without symptoms associated with FGIDs were allotted to the control group. As expected, all 988 preterm-born infants displayed considerable differences (variations) in gestation time, birth weight, the incidence of cesarean delivery, rate of breastfeeding, antibiotic usage, the addition of probiotics, and maternal history of smoking, anxiety, and hospital stay (Table 1). There were no considerable variations in gender between the case group and the control group.
It was observed that the prevalence of FGIDs among preterm newborns varied considerably in terms of gestational age (χ2 = 21.83; p <0.001), especially in the case of infant colic (χ2 = 28.10; p <0.001) and infant regurgitation (χ2 = 33.13; p <0.001) (Table 2).
In addition, there were also found differences in infants according to the different weight at birth in at least one FGIDs (χ2 = 16.00; p = 0.003), infant colic (χ2 = 27.18; p <0.001), and infant regurgitation (χ2 = 18.11; p <0.001) (Table 3). There was no significant difference in others.
There are several neonatal risk factors associated with FGIDs, as shown in Table 4. (see Additional file 4). Univariate analysis has revealed that FGIDs were significantly associated with gestational age, birth weight, cesarean delivery, breastfeeding, exclusive formula feeding, use of neonatal antibiotics and probiotics, maternal anxiety, maternal smoking, and hospitalization longer than 7 days (Table 4). The risk from infantile colic [(<28 weeks: OR = 5.28, 95%CI = 1.10-12.4, p = 0.003), (28-32 weeks: OR = 4.16, 95%CI = 1.05-11.5, p = 0.008)] and infant regurgitation [ (<28 weeks: OR = 4.12, 95%CI = 0.63-11.3, p = 0.045) (28 - 32 weeks: OR = 3.28, 95%CI = 1.18-12.4, p = 0.049)] was considerably elevated for infants with low gestational age. Moreover, the risk from infantile colic [(<1 kg: OR = 6.84, 95%CI = 2.35-15.6, p = 0.004), (1-1.5kg: OR = 4.21, 95%CI = 1.58-13.2, p = 0.023)] and infant regurgitation [(<1 kg: OR = 2.57, 95%CI = 0.86-5.38, p = 0.012), (1-1.5kg: OR = 1.26, 95%CI = 0.91-6.39, p = 0.035)] was considerably high for infants with lower weight on birth. In addition, if the infant was delivered by cesarean, the risk of functional constipation was higher (OR = 1.99, 95%CI = 1.31-3.18, p = 0 .015). Furthermore, infants exclusively fed with formula following birth have displayed a higher risk for infantile regurgitation (OR = 2.02, 95%CI = 1.32-1.38, p = 0.009). Infant colic was significantly associated with the duration of antibiotic use in the neonatal period [(8-14 days: OR = 2.69, 95%CI = 1.29-4.37, p = 0.006), (> 14 days: OR = 3.24, 95%CI = 1.06-5.45, p <0.001)]. The use of probiotics in the first month of life was considerably associated with infant colic [(age of probiotics initiation ≤14 days, OR = 1.36, 95%CI = 1.21-2.89, p = 0.062), (Duration of probiotics use >14 days, OR = 1.37, 95%CI = 1.24-2.92, p = 0.032)] and functional constipation [(age of probiotics initiation ≤14 days, OR = 0.93, adjusted 95%CI = 0.37-1.29, adjusted p =0.002), (duration of probiotics use >14 days, OR = 0.88, adjusted 95%CI = 0.63-1.19, P = 0.009)]. maternal anxiety (OR = 3.23, 95%CI = 2.83-10.5, p = 0.023), maternal smoking (OR = 2.15, 95%CI = 1.38-3.34, p = 0.005), and hospitalization longer than 7 days (OR = 2.17, 95%CI = 1.32-2.48, p <0.001) were also considerably associated with infant colic. Furthermore, there were no other significant associations were found.
The results of the multivariate logistic regression analysis are shown in Table 5 (see Additional file 5). Infant colic was substantially linked to a gestational age of 32 weeks or less and birth weight of 1.5 kg or less [(gestational age < 32weeks: adjusted OR = 4.08, adjusted 95%CI = 2.37-12.1, adjusted p = 0.013), (birth weight < 1.5kg: adjusted OR = 3.26, adjusted 95%CI =2.48-10.5, adjusted p = 0.026)] and infant regurgitation [(gestational age < 32weeks: adjusted OR = 3.25, adjusted 95%CI = 2.19–6.84, adjusted p = 0.027), (birth weight < 1.5kg: adjusted OR = 2.78, adjusted 95%CI =1.48–5.25, adjusted p = 0.015)]. Cesarean delivery (adjusted OR = 2.74, adjusted 95%CI = 1.28-11.3, adjusted p < 0.001) was considerably linked to functional constipation. Antibiotic use over 8 days (adjusted OR = 2.93, adjusted 95%CI = 1.28-5.39, adjusted p <0.001), maternal smoking (adjusted OR = 2.43, adjusted 95%CI = 1.57-4.29, adjusted p = 0.004), and hospitalization longer than 7 days (adjusted OR = 2.27, adjusted 95%CI = 1.36-5.62, adjusted p <0.001) were considerably linked to infantile colic. There was a considerable association between colic in infants and probiotic use lasting more than 14 days (duration of probiotics use >14 days, adjusted OR = 0.85, adjusted 95%CI = 0.65-1.23, adjusted p = 0.005) and functional constipation (duration of probiotics use >14 days, OR = 0.84, adjusted 95%CI = 0.46-1.47, p = 0.02). Following birth, both exclusive breastfeeding (adjusted OR = 0.87, adjusted 95%CI = 0.36-1.92, adjusted p = 0.003) and formula feeding (adjusted OR = 1.84, adjusted 95%CI =1.21-3.83, adjusted p = 0.011) were considerably linked to infant regurgitation.