What developmental milestone should be monitored at the 9-month check-up?

At the 9-month check-up, one key developmental milestone to monitor is the ability to sit without support. By this age, most infants develop the necessary muscles and coordination to sit independently for extended periods. This milestone is an important indicator of an infant's overall physical development and is closely linked to other developmental skills, such as balance and core strength.

While the ability to crawl, first words spoken, and weight gain progression are also important factors, they are either more characteristic of other age ranges or not as definitive in assessing the baby’s developmental status for this specific age. Crawling often begins around 9 months, but not all infants crawl at the same time. Speech development is typically observed around the 12-month mark when first words are commonly said. Weight gain, while essential to monitor for health and growth, does not reflect motor or cognitive development in the same way that the ability to sit without support does.