Our 9-month-old baby girl was born full-

Answer

Not the act-now lane — no seizure, no breathing trouble, no lost skills, no blue/gray colour. She is full-term and 9 months, so we use the **CDC 9-month card** straight, no corrected age.

**What the 9-month card says vs. what she does**

| 9-month CDC item | She |
| --- | --- |
| Makes sounds like "mamamama" / "bababababa" | ✓ babbles ba-ba, da-da |
| eaches / moves things between hands | ✓ reaches for toys |
| olls both ways | ✓ both ways |
| Gets to a sitting position by herself | ? (you only described being placed) |
| **Sits without support** | ✗ slumps forward or flops after a second or two |

Source: https://www.cdc.gov/act-early/milestones/9-months.html (accessed 2026-09-02)

"Sits without support" is on the 9-month card, and she is not there yet. One missed item on the matching card is not a diagnosis — but it is the kind of thing CDC and AAP say you raise with her doctor, not something to wait out.

**What the WHO window actually means**

For sitting without support, the WHO window is **3.8–9.2 months** (1st–99th percentile of healthy children). Source: https://www.who.int/tools/child-growth-standards/standards/motor-development-milestones (accessed 2026-09-02).

That band is **population variation**, not your daughter's percentile and not a pass/fail line. She sits at the very upper end of that band, not past it. The band also overlaps the other motor windows — children do not hit the six gross-motor skills in lockstep. None of that turns "doesn't sit yet" into "nothing to ask about".

**About the in-laws' "must sit by 6 months"**

That is not what CDC or WHO say. The CDC 6-month card lists *"leans on hands to support herself when sitting"* — that is propped sitting, not independent sitting. "Sits without support" first appears on the **9-month** card, and the WHO band reaches 9.2 months. So 6 months is a folk line, not a clinical one.

**Today's two rows**

| When | What |
| --- | --- |
| Today, 2026-09-17 | Write down: "9 months, full-term. Does not sit without support — slumps or flops after ~2 s when placed. olls both ways, reaches, babbles ba-ba/da-da." Note which items she can and cannot do on the 9-month card. |
| At her upcoming 9-month visit | Ask the doctor for a **formal developmental screening**, not just a look in the room. A screening is a standardised tool, separate from the CDC checklist. Source: https://www.cdc.gov/act-early/about/developmental-monitoring-and-screening.html (accessed 2026-09-02) |

A visit already on the calendar is where that request gets made — not a reason to wait for a later one.

**Visit checklist to bring**

Dated, from the CDC "share with the doctor" prompts:

1. **Your concern, in one line.** "She does not sit without support at 9 months."
2. **What she used to do / what she does now.** olls both ways, reaches, babbles ba-ba/da-da; placed in sitting → slumps or flops after ~2 s.
3. **Lost any skills?** No. (If yes at any point, tell them the same day.)
4. **Born prematurely?** No, full-term.
5. **Hearing:** does she turn when you call her name in a quiet room? date.
6. **Language:** sounds/word-attempts in every language used at home; date.
7. **Gestures:** pointing, showing, waving — yes/no, date.
8. **Eye contact / showing:** does she bring a toy to show you or look to check you are close? date.
9. **Motor:** sitting — yes/no, new stiffness or floppiness — yes/no, uses both sides — yes/no, date.
10. **equest:** formal developmental screening at this visit, and a referral if anything is still unclear afterwards.

Source: https://www.cdc.gov/act-early/milestones/9-months.html (accessed 2026-09-02) · https://www.cdc.gov/act-early/about/developmental-monitoring-and-screening.html (accessed 2026-09-02)

If you want, I can also write this as a one-page PDF to hand to the doctor — say the word.

Does she ever get into a sitting position by herself (rolling or pushing up from tummy), or only ever end up there when you place her?