Study population and breastfeeding rates

A total of 3542 mother-infant dyads were originally recruited to the CHILD study. A total of 2906, 2587 and 2593 participants indicated their breastfeeding status at 3, 6 and 12 months respectively and were included in this analysis, with 2060 providing breastfeeding data at all three timepoints. Characteristics of BFW and NBFW are described in Table 1. A total of 87.4% (n = 2540/2906), 75.3% (n = 1948/2587), 45.5% (n = 1180/2593) of participants were breastfeeding at 3, 6 and 12 months respectively. Breastfeeding women were found to be older and more educated than non-breastfeeding women. Women who were breastfeeding at 3 months and 6 months postpartum had higher annual household income than their non-breastfeeding counterparts however this trend did not persist at 12 months postpartum. There was a higher proportion of women who breastfeeding than not breastfeeding in Vancouver at 3, 6 and 12 months postpartum however lower breastfeeding proportions were found in Edmonton and Manitoba at these time points. Toronto had equivalent proportion of breastfeeding versus non-breastfeeding women at 3 and 6 months postpartum however lower breastfeeding rates at 12 months postpartum.

Patterns of medication usage in BFW and NBFW

The number of prescription medications used by BFW and NBFW was not significantly different at 3, 6 and 12 months postpartum. At 3 months postpartum, 41.9% of BFW and 45.9% of NBFW reported using at least one prescription medication during the first 3 months postpartum. At 6 months postpartum, 29.5% of BFW and 30.7% of NBFW reported using at least one prescription medication during the 3–6 months postpartum period. At 12 months postpartum, 32.8% of BFW and 37.6% of NBFW reported using at least one prescription medication during the 6–12 months postpartum period. Domperidone was among the top 3 most commonly used prescription medication by BFW at 3, 6 and 12 months. Given that domperidone was largely used for lactation purposes, it was initially thought that it could have contributed to the large number of breastfeeding women taking prescription medications in this study as shown in Fig. 1. However, even when domperidone was excluded from the data, there were no differences in the number of prescriptions that that were reported by BFW and NBFW.

In contrast, when comparing usage of NPM, there were significantly more BFW who reported using at least one NPM than NBFW. At 3 months postpartum, 67.6% of BFW and 48.9% of NBFW used at least one NPM (p < 0.0001). The median (range) number of NPM used at 3 months is 1 (0–12) and 0 (0–8) for BFW and NBFW women respectively. At 6 months postpartum, 47.8% of BFW and 30.5% of NBFW used at least one NPM (p < 0.0001); 0 (0–14) vs. 0 (0–10). At 12 months postpartum, 46.9% of BFW and 39.6% of NBFW used at least one NPM (p < 0.001); 0 (0–12) vs. 0 (0–10).

Most commonly used medications and their indications

The ten most commonly used prescription medication by BFW at 3, 6 and 12 months are shown in Fig. 2. The five most commonly used prescription medication by BFW at 3 months was domperidone (9.0%, n = 229/2540), norethisterone (5.0%, n = 128/2540), levothyroxine (4.3%, n = 108/2540), cephalexin (3.7%, n = 94/2540), amoxicillin (2.7%, n = 68/2540).

Fig. 2

The 10 most common prescription medications used by breastfeeding mothers during the first 3 months, 3 to 6 months, and 6 to 12 months in the CHILD Cohort Study. Usage compared to non-breastfeeding mothers. * denotes statistical significance

Tables 2, 3 and 4 contain the ontologized self-reported reasons for use of these top ten medications for each time point in the same respective order. The self-reported reasons for medication use of domperidone included off-label use to manage lactation (signifying unapproved use of an approved medication). Breastfeeding mothers reported using the antimicrobials cephalexin (3.7%, n = 94/2540), amoxicillin (2.7%, n = 68/2540), cloxacillin (1.4%, n = 35/2540) and nystatin (1.3%, n = 24/2540) to combat mastitis, unspecific infections, and other breast abnormalities. The complete lists of prescription and NPMs and their usage pattern by BFW and NBFW are shown in Additional file 2 and 3.

The five most common NPMs used by BFW at 3 months was multivitamin (48.3%, n = 1226/2540), vitamin D (16.5%, n = 419/2540), acetaminophen (10.4%, n = 264/2540), calcium (8.4%, n = 213/2540), omega 3 (8.0%, n = 203/2540). The five most common non-prescription medications used by BFW at 6 months was multivitamin (28.9%, n = 563/1948), acetaminophen (11.8%, n = 230/1948), vitamin D (11.5%, n = 224/1948), ibuprofen (7.6%, n = 148/1948), calcium (5.3%, n = 103/1948). The five most common non-prescription medications used by BFW at 12 months was multivitamin (25.9%, n = 306/1180), vitamin D (12.5%, n = 148/1180), acetaminophen (11.6%, n = 137/1180), ibuprofen (9.4%, n = 111/1180), omega 3 (5.4%, n = 64/1180). Indications were not reported for NPMs.

Medication use by site

The most common prescription medications and NPM for each time point were also compared by study site for BFW to evaluate regional patterns as seen in Additional file 2 and 3. At 3 months (but not 6 or 12 months), there was a significant difference for the usage of domperidone in BFW between participant sites, with higher usage in Vancouver compared to the other sites (Edmonton 8.8%, 46/521; Toronto 7.5%, 46/613; Vancouver 13%, 86/661; Manitoba 6.8%, 51/745; <0.001). For NPM at 3 months postpartum, there was a significance difference for the usage of multivitamins for BFW, with more than 2-fold higher usage in Vancouver compared to Manitoba (Edmonton 45.3%, 236/521; Toronto 54.5%, 334/613; Vancouver 69.9%, 462/661; Manitoba 26.3%, 196/745; <0.0001). These differences persisted at 6 months but were no longer evident at 12 months. At 12 months, there was a significant difference observed for norethisterone usage in BFW, with higher usage in Edmonton and Manitoba compared to Toronto and Vancouver (Edmonton 8.1%, 17/211; Toronto 2.4%, 5/209; Vancouver 1.3%, 5/400; Manitoba 5.8%, 21/360; <0.0001).

Pattern of medication use based on therapeutic categories in BFW and NBFW

Prescription medications and other medications used by women postpartum are shown in Fig. 1, grouped into therapeutic categories. There were several significant differences in therapeutic class usage frequency between BFW and NBFW. At 3 months postpartum, BFW were more likely to use supplement/herbal remedies (20.4% versus 8.7%, < 0.0001) and vitamins/minerals (53.1% versus 28.1%, < 0.0001), whereas NBFW were more likely to use opioid analgesics (2.1% versus 5.5%, 0.003) and psychotropic agents (4.3% versus 11.2%, < 0.0001). At 6 months, BFW remained more likely to use supplement/herbal remedies (11.3% versus 3.9%, < 0.0001) and vitamins/minerals (33.2% versus 12.1%, < 0.0001) and were also more likely to use gastrointestinal agents (10.3% versus 4.9%, 0.0001); NBFW remained more likely to use psychotropic agents (4.4% versus 8.8%, < 0.0001). At 12 months, BFW remained more likely to use vitamins/minerals (31.1% versus 19.2%, < 0.0001) but no other differences were observed. All other therapeutic categories, such as non-opioid analgesics, anti-infectives, cardiovascular agents, etc., had no observed significant differences in the breastfeeding versus the non-breastfeeding groups.