Our study showed that the percentage of women with exclusive breastfeeding at one month after delivery among the women who received labor neuraxial analgesia was 43.1% (n = 163/376). Significant predictors of impairment of the initiation of exclusive breastfeeding were oxytocin use, vacuum extraction delivery and lower birthweight of infants.
In this retrospective cohort study, the rate of successful initiation of exclusive breastfeeding in women who received labor neuraxial analgesia at one month was 43.1%, which was lower than the rate at one month for all deliveries in Japan (51.3%) [7]. In a 20-day postpartum study by Mauri et al., the rate of exclusive breastfeeding among women who received epidural analgesia was 68.9% [10], and Mahmoodi et al. reported an exclusive breastfeeding rate of 81.4% at one month postpartum among women who received epidural analgesia [11]. On the other hand, some studies have shown that the groups that received epidural analgesia had lower rates of breastfeeding (43-51.5%) within 6 weeks postpartum compared with the rates of breastfeeding in the groups that did not receive epidural analgesia [12, 13]. In addition, a systematic review of studies on the effects of labor neuraxial analgesia showed heterogenous results [6]. The effects of labor neuraxial analgesia on the rate of exclusive breastfeeding have therefore been unclear.
Oxytocin use and vacuum extraction delivery as mother-related factors and lower birthweight as an infant-related factor were identified as significant predictors of impairment of exclusive breastfeeding in our study. Birthweight was reported in a previous study to be an important predictor of exclusive breastfeeding after caesarean section and vaginal delivery [14]. Infant breast milk energy intake was shown to be positively associated with birthweight [15]. Lower birthweight infants did not promote the establishment of adequate milk production due to weak suckling [16] and may have lower rates of exclusive breastfeeding.
Epidural analgesia has been associated with prolongation of the second stage of labor [17]. The use of oxytocin is considered in cases in which labor is prolonged or if weak labor persists. Labor epidural analgesia in combination with oxytocin infusion negatively influenced endogenous oxytocin levels, and women who received oxytocin infusion at delivery reportedly had lower levels of endogenous oxytocin at lactation on the second postpartum day [18]. A systematic review of the long-term effects of administration of oxytocin during peripartum suggested that exogenous administration of oxytocin might negatively impact upon breastfeeding [19], which is supportive of our findings. Oxytocin administration may decrease endogenous oxytocin and reduce the rate of postpartum lactation.
Vacuum extraction delivery has not previously been reported as a risk factor for breastfeeding, regardless of whether neuraxial analgesia was received during labor. Vacuum delivery is used in cases with a prolonged second stage of labor. The mother is more likely to experience stress during delivery if she has undergone a prolonged delivery or multiple delivery interventions [12]. Maternal stress during childbirth may inhibit oxytocin secretion after delivery and adversely affect breastfeeding [20]. We expected that a history of smoking before pregnancy would be negatively associated with exclusive breastfeeding because maternal smoking was identified as a factor that impairs exclusive breastfeeding [5]. However, such a relationship was not found in our study. This could be because we did not examine smoking during pregnancy or smoking after delivery because the medical records were not available for all of the women.
This study has some limitations. The decision regarding oxytocin use or vacuum extraction was left to the discretion of each obstetrician. Previous studies including both women who did and did not receive labor neuraxial analgesiashowed that risk factors for impairment of exclusive breastfeeding were infant-mother separation, maternal educational attainment, breastfeeding education received by the mother or parents, parenting stress, and maternal income [5][8]. However, those were not included as variables in our study because the relevant data was not recorded.