The provision of breast milk is essential for preterm infants as it provides unique health benefits that are unmatched by other types of feeding [1–3]. However, breastfeeding presents unique challenges for preterm infants that include establishing and maintaining the mothers' milk supply and transitioning the infant from gavage feeding to breastfeeding [4]. One of the issues that presents during the transition to breastfeeding is that mothers of preterm infants are rarely available for all oral feedings during hospitalization; making it necessary for infants to receive oral feedings by other methods, usually bottle feeding.

However, exposure of newborn infants to artificial nipples has been strongly associated with breastfeeding problems [5–9]. Frequently these problems have been explained by a phenomenon called nipple confusion. Nipple confusion occurs when infants are exposed to two different feeding methods, bottle and breast, resulting in the infant refusing to breastfeed [10]. Consequently, it has been recommended that bottle feeding be avoided and that cup feeding be used for the supplementation of term [11, 12] as well as preterm infants [13–15].

Cup feeding is known as an alternative method of feeding breast milk to an infant using a small cup without a lip [16, 17]. Cup feeding is also recommended by the Baby Friendly Hospital Initiative [18]. The use of the cup for feeding newborn infants was originally based on the goal of avoiding propping up of bottles and also to increase bodily contact with the mother during feeding [19]. Although cup feeding receives little mention in medical literature, and may seem to be a new technique for some, cup feeding has been used in several developing and developed countries [16]. Lang, who observed cup feeding in South Nepal, implemented cup feeding in England and the practice expanded to other developed countries. Consequently cup feeding was established as a method for feeding infants who could not be breastfed from birth [15].

The findings of studies concerning breastfeeding outcomes of cup fed infants have been inconsistent. A Cochrane review [20] concluded that cup feeding cannot be recommended over bottle feeding as a supplement to breastfeeding because cup feeding had no significant benefit in maintaining breastfeeding beyond hospital discharge. Also, the review suggested that cup feeding had the potential for the unacceptable consequence of a longer hospital stay. A randomized controlled trial [21] compared the impact of cup or bottle supplementation for preterm infants on subsequent breastfeeding at discharge from the hospital. No significant differences were found between the bottle and cup feeding infants in terms of whether they were breastfeeding or not at discharge from the hospital. However, the small sample size (n = 12) may have contributed to the lack of differences. In contrast, another report suggested that infants in special care units who are supplemented by cup are more likely to breastfeed longer than those supplemented by bottle [22].

Cup feeding has not been implemented in Egypt, making evaluation of its use essential. Additionally, given the absence of definitive evidence as to the most effective method of supplementation for preterm infants during hospitalization and the effects of cup feeding on breastfeeding patterns after hospital discharge, the purpose of the current study was to examine the effect of cup feeding on breastfeeding in late preterm infants after discharge. The following research questions were addressed: (1) Are premature infants supplemented by cup during hospitalization more likely to be fully breastfed six weeks after discharge when compared to premature infants supplemented by bottle during hospitalization?, and (2) Do preterm infants supplemented by cup during hospitalization demonstrate more mature breastfeeding behavior at 1, 2, 3, 4, 5, and 6 weeks after discharge when compared to preterm infants supplemented by bottle?

Findings of the current study should be interpreted in the light of the following limitations. First, a randomized experimental design could not be used because the introduction of cup feeding would have been a threat to internal validity through the possible diffusion of cup feeding to the control group. Consequently, randomization was not possible. Second, the principal investigator collected all of the data, including the assessments of breastfeeding behavior after discharge. Thus, the PI was not blinded to group assignment or to the purpose of the study. Further study using independent data collectors who are blind to group assignment and purpose is required to overcome these limitations. Third, it was intended that determination of breastfeeding practices would have continued longer after discharge. However, 56% of the mothers had either only some or no education so that long term written documentation was not feasible. Additionally, concerns regarding accuracy of maternal verbal recall were present. These concerns were minimized by recording breastfeeding practices for the first week after discharge only. Use of a simple feeding diary is recommended for future studies. Finally because of the loss to follow up, the sample was too small to adequately answer the primary research question. Future research needs to be planned using a larger sample size to account for attrition. Despite the limitations, the current study was the first to implement cup feeding for preterm infants in Egypt and was one of the few studies to use cup feeding as the only oral feeding method for preterm infants during hospitalization [5, 13, 14].

All 60 mothers intended to breastfeed after discharge. Even though, only 17 infants in the bottle feeding group and 20 infants in the cup feeding group had breastfeeding experiences during hospitalization. The low incidence of breastfeeding during hospitalization is most likely a result of many factors, including infrequent visiting and lack of encouragement of the mothers to be actively involved in their infants' care during visitation. Consequently, 38% of the infants were discharged with no breastfeeding experiences during hospitalization. Despite this, the overall mean proportion of feedings that were breast feeding for the entire group one week after discharge was 72%, with a significantly higher proportion in the cup feeding group when compared to the bottle feeding group. Infants in the cup feeding group had significantly more breastfeedings per day one week after discharge from the hospital than infants in the bottle feeding group, suggesting that the transition to breastfeeding progressed more quickly for cup feeding infants than for bottle feeding infants. The lack of exposure of cup fed infants to oral mechanisms used during bottle feeding, which are different than the oral mechanisms used during breastfeeding, [17] might facilitate adaptation to breastfeeding. However, the explanation for this finding is unclear [28].

Sipping and lapping used during cup feeding has been theorized to enhance development of tongue movements needed for breastfeeding [17]. However, the mechanisms of sipping and lapping differ from those required during breastfeeding [7, 28]. Sipping and lapping require the lips to be closed, rather than open, as required during breastfeeding and to a lesser extent during bottle feeding. Differences in mouth contour, activity of the masseter, temporalis and buccinators muscles, and the position of the lips between cup, bottle and breastfeeding may contribute to subsequent breastfeeding difficulties [29]. A recent electromyographic study carried out during cup feeding, bottle feeding and breastfeeding found that the range of contraction and mean contraction of the masseter muscle were greater during cup feeding than during bottle feeding [10]. This finding supported the recommendation that if breastfeeding is not possible at certain times, cup feeding may be indicated, as it allows the participation of the masseter and temporalis muscles in a way that is similar to the participation of these muscles during breastfeeding [10]. These differences in oral mechanisms underlie the differences found in breastfeeding patterns when alternative methods such as bottle feeding have been used for supplementation of the breastfeeding infant.

An increased prevalence of breastfeeding has been reported when bottle feeding was replaced by cup feeding for preterm infants [17, 20] as well as full term infants [12]. The findings of the current study are consistent with a recent randomized controlled trial [14] that found that cup feeding significantly increased the odds of breastfeeding at discharge. Additionally, Collins et al. reported a significant increase in the prevalence of breastfeeding at three and six months after discharge for infants fed by cup during hospitalization when compared with bottle supplementation [13]. In contrast, another randomized controlled trial provided unclear evidence of the effect of using cup or bottle for feeding preterm infants on breastfeeding [14]. No differences in breastfeeding prevalence at the first return visit between infants fed by cup and infants fed by bottle during hospitalization were found. At the first visit, 56% of bottle fed infants and 57% of cup fed infants had already been weaned and both groups presented similar breastfeeding prevalence. However, the percentage of infants still breastfeeding was two times greater in the cup fed group.

Although there were no statistically significant differences in the current study between cup feeding and bottle feeding groups regarding their breastfeeding type (full or partial) one week after discharge, more infants were exclusively breastfed in cup feeding group than in the bottle feeding group (Figure 2). These results are consistent with previous cup feeding studies [13, 19] that reported that cup feeding significantly increased the likelihood that the preterm infants would be fully breast fed at hospital discharge. Additionally, it has been demonstrated that exclusivity of breastfeeding at one month after birth predicted the likelihood of continuing breastfeeding at six months [30]. In the current study it is possible that the shorter duration of cup feeding (9.1 days ± 5.61) than bottle feeding (12.5 days ± 8.20) resulted in these more optimal findings, as infants in the cup feeding group had less exposure to a feeding method other than breastfeeding. However, these findings were not significantly different, suggesting that it is the process of cup feeding rather than the duration of the feeding method that contributed to the better breastfeeding for the cup feeding group. In contrast to the suggestion of a recent Cochrane review [20], the length of hospital stay was shorter for the cup fed infants.

The second research question examined the maturation of breastfeeding behaviors from one through six weeks after discharge for both cup and bottle groups. The study findings demonstrated statistically significant differences between the cup and bottle feeding groups in their total breastfeeding behavior scores from the first-to-the sixth week after hospital discharge, reflecting higher mean PIBBS scores at each time point for the cup fed infants than the bottle fed infants. Additionally, infants in both groups showed an increase in their PIBBS scores over the six weeks, indicating a maturation of breastfeeding behavior over time. These findings are consistent with those of Nyqvist [31].

There was a significant interaction effect between group and time, demonstrating that, although both groups demonstrated expected maturation of breastfeeding behaviors, cup fed infants were significantly more mature in their breastfeeding behaviors at all time points than bottle fed infants, despite the cup feeding infants having statistically significant younger ages at discharge. The finding of improved breastfeeding behavior maturation among cup fed infants may be related to the higher breastfeeding proportion for this group, in that more breastfeeding experience may promote the maturation of breastfeeding behaviors. Conversely, more mature breastfeeding behavior may promote the frequency of breastfeeding.

Most previous studies have been concerned only with descriptions of infants' sucking and swallowing behavior [30], physiologic responses [32, 33], and milk transfer [34]. Nyqvist, (1996) developed the PIBBS and used the instrument to describe the behaviors of breastfeeding preterm infants. However, the current study is the first to use the PIBBS to compare groups of breastfeeding preterm infants in relation to the method of supplementation [25]. A recent report used the PIBBS to evaluate breastfeeding behaviors for two groups of term infants to determine if epidural anesthesia had an effect on breastfeeding behaviors. There were no statistically significant differences found between the groups [35]. However, the PIBBS was not an appropriate instrument for use in that study as it had been developed for use with preterm infants. Future research should focus on the use of the PIBBS to compare preterm infants in relation to a variety of different experiences this population may have during the transition to full oral feeding.

Cup fed infants were more exclusively breast-fed after discharge, supporting the Baby Friendly Hospital Initiative recommendations for using cup feeding and avoiding bottle feeding when providing supplementation for preterm infants. The current study provides initial evidence for the implementation of cup feeding as a method of supplementation during hospitalization. If cup feeding is implemented in Egypt it will be necessary to first educate the medical and nursing staff. All healthcare personnel need to promote breastfeeding as the best and natural feeding method for all infants. Additionally, healthcare providers need to accept cup feeding as a safe, efficient feeding method and to learn safe cup feeding techniques. The finding that most mothers in both groups were able to initiate breastfeeding after discharge is interesting. Mothers did not have access to an electric breast pumps and did not provide breast milk to infants during hospitalization. Therefore, it is not known how mothers established and maintained their milk supply. These findings draw attention to the need for further exploration of the methods used by mothers of preterm infants to maintain their milk supply during infant hospitalization.