First-week feeding category and time to first recorded formula-only milk feeding through six months postpartum: a discrete-time survival analysis of a hospital follow-up cohort

For many new parents, the first few months after a baby arrives are defined by a single, pressing question: how will we feed this child? Health organizations around the world recommend that mothers breastfeed exclusively for the first six months, meaning the baby receives only breast milk and no other liquids or foods. Yet, in many modern settings, including Taiwan, a large number of women who start breastfeeding find themselves switching to formula milk as the baby's only source of nutrition long before that six-month mark arrives. This shift is not just a matter of personal choice; it often happens because of real challenges in establishing a milk supply, difficulties with the baby latching on, or the physical and emotional toll of the postpartum period. Understanding exactly when this transition happens, and what early signs might predict it, is crucial for doctors and nurses who want to offer support at the right moment.

A team of researchers in Taiwan recently set out to map this journey using data from a hospital follow-up program. They followed hundreds of women who were providing some breast milk one week after giving birth, tracking them at regular intervals up to six months. Their goal was to pinpoint the exact moment a mother's feeding routine changed so that formula became the sole source of milk for her baby. They also wanted to see if the way a mother was feeding her baby in that very first week—whether directly at the breast, using expressed milk from a bottle, or already mixing breast milk with formula—could serve as an early warning sign for when that switch to formula-only feeding might occur.

The study, conducted at a major hospital in northern Taiwan, gathered information from 651 women who had given birth between late 2021 and late 2024. These women were part of a structured program where nurses checked on them and their babies at one week, one month, two months, four months, and six months after delivery. At each visit, the nurses recorded how the baby was being fed. The researchers focused specifically on the women who were giving their babies any amount of breast milk at the one-week mark, excluding those who were already feeding exclusively on formula. The main event they were looking for was the first time a record showed that the baby was receiving only formula milk, with no breast milk at all.

The results revealed a clear pattern in the timing of this transition. By the time the babies reached six months of age, nearly two-thirds of the mothers in the study had reached a point where formula was the only milk their baby received. The researchers found that this change did not happen all at once; instead, it was heavily concentrated in the first four months after birth. The highest risk of making this switch occurred between the first and second month of the baby's life. While the largest number of total switches happened between the second and fourth months, this was partly because that time period covers a longer stretch of time. When adjusted to a monthly rate, the period between one and two months stood out as the most critical window.

The study also uncovered strong clues about which mothers were most likely to face this transition. The most significant predictor was found in the feeding category recorded just one week after birth. Mothers who were already mixing breast milk with formula at that first week were much more likely to switch to formula-only feeding later on compared to those who were feeding exclusively with breast milk. Among those feeding with breast milk, the method mattered too. Mothers who were feeding directly at the breast had the lowest chance of switching to formula-only, while those who were feeding only expressed breast milk from a bottle had a higher chance, though still lower than the mixed-feeding group. This suggests that the way a mother feeds her baby in the first week carries important information about the future of her feeding journey.

Other factors were also examined. The researchers found that mothers who had delivered their babies via Cesarean section were more likely to switch to formula-only feeding compared to those who had vaginal births. Older mothers tended to have a lower risk of making the switch, while the number of children a woman had previously given birth to did not show a clear independent link once the feeding method was taken into account. Interestingly, the study did not find strong evidence that maternal depression scores, a history of breast inflammation known as mastitis, or living in a postpartum care center during the first week significantly changed the odds of switching to formula-only feeding, although the data did not rule out the possibility of a smaller effect.

The authors emphasize that their findings describe a pattern of association rather than a cause-and-effect relationship. Because the study looked back at records of what happened, it cannot prove that feeding directly at the breast causes a mother to continue breastfeeding for longer. Instead, the feeding category recorded in the first week acts as a powerful early marker. A mother who is already mixing formula at one week is likely already facing challenges or has made a choice that places her on a different path. The study suggests that healthcare providers can use this early information to identify families who might benefit from extra support and discussion about their feeding goals before the baby turns one month old, and certainly before the four-month mark when the risk of switching remains high.

This research highlights that the period of vulnerability for breastfeeding extends well beyond the immediate days after birth. While the first month is often the focus of medical attention, the data shows that the transition to formula-only feeding is a process that unfolds over the first four months, with a particularly steep climb between the first and second month. By paying close attention to how a mother is feeding her baby in that first week, and by recognizing the specific risks associated with Cesarean delivery, medical teams can better tailor their support. The goal is not to force a specific method, but to offer preference-sensitive help that aligns with what each family needs, ensuring that the decision to switch to formula is a supported one rather than a result of unaddressed difficulties.