Body system 100.00 in the SSA Blue Book covers low birth weight and failure to thrive for children (Part B). SSA uses these listings at step 3 of its five-step disability evaluation. If your medical evidence meets one of the listings on this page, your claim is approved without the disability examiner moving on to past-work and labor-market analysis at steps 4 and 5.
Most claimants who do not meet a listing in this body system can still be approved at later steps based on their residual functional capacity, age, education, and past work. The medical evidence you build for a listing-match argument is the same evidence those later steps rely on, so the listing criteria are useful to read even when a claim looks like a step-5 approval candidate.
Body system code
100.00
Part B (children)
Active listings
2
Specific impairments
Audience
Children under 18
SSA disability evaluation
Step in evaluation
3 of 5
Listing match approves the claim
Active listings under 100.00
Every listing below has current SSA-published criteria. Codes that SSA reserved for future use or has withdrawn since 1985 are not included. Click a listing where a plain-English breakdown is available, or follow the regulation link for SSA's exact text.
| Code | Listing | Reference |
|---|---|---|
| 100.04 | Low birth weight in infants from birth to attainment of age 1 | ssa.gov |
| 100.05 | Failure to thrive in children from birth to attainment of age 3 | ssa.gov |
Source: SSA Blue Book, body system 100.00. Last synced 2026-05-04.
How SSA describes this body system
Excerpted from SSA's regulatory introduction at the top of the body-system page. Full text and all subsection cross-references live on ssa.gov.
A. What conditions do we evaluate under these listings? We evaluate low birth weight (LBW) in infants from birth to attainment of age 1 and failure to thrive (FTT) in infants and toddlers from birth to attainment of age 3. B. How do we evaluate disability based on LBW under 100.04? In 100.04A and 100.04B , we use an infant's birth weight as documented by an original or certified copy of the infant's birth certificate or by a medical record signed by a physician. Birth weight means the first weight recorded after birth. In 100.04B , gestational age is the infant's age based on the date of conception as recorded in the medical record. If the infant's impairment meets the requirements for listing 100.04A or 100.04B , we will follow the rules in § 416.990(b)(11) of this chapter. C. How do we evaluate disability under 100.05 ? 1. General. We establish FTT with or without a known cause when we have documentation of an infant's or toddler's growth failure and developmental delay from an acceptable medical source(s) as defined in § 416.913(a) of this chapter. We require documentation of growth measurements in 100.05A and developmental delay in 100.05B or 100.05C within the same consecutive 12-month period. The dates of developmental testing and reports may be different from the dates of the growth measurements. After the attainment of age 3, we evaluate growth failure under t...
Read the full text on the SSA Blue Book 100.00 page.
What happens during a claim under 100.00
The disability examiner assigned to your claim looks for medical records that match the lettered criteria of one of the listings above. The examiner does not diagnose you and does not weigh symptoms in isolation. They line up the listing's required findings against your records and decide whether the records contain enough to satisfy the listing as written.
If your records meet a listing, the claim is approved at step 3. If not, the examiner moves on to evaluating your residual functional capacity (RFC) at steps 4 and 5. RFC is a description of what work activity you can still do despite your impairments. The listings inform the RFC because the same medical evidence the listings ask for is the evidence the examiner uses to write the RFC. The disability overview walks through the full five-step evaluation in plain English.
Work activity, SGA, and the SSDI gate
A claim under any Blue Book listing is denied at step 1 if you are working at or above the substantial gainful activity threshold. SGA is the monthly earnings test SSA applies before any medical evaluation. Earning above SGA in countable work activity means SSA never reaches the listings on this page. Earning below SGA, or being out of work entirely, lets the medical evaluation proceed.
Once you are approved and receiving SSDI, the trial work period and extended period of eligibility apply differently than at the initial-application stage. Both are explained on the SGA amount page with year-by-year thresholds since 1975.