# Grobman 2007 VBAC Probability Calculator (First Prenatal Visit)

> Grobman 2007 VBAC Probability Calculator (First Prenatal Visit) is a paid API for AI agents from api.magentlab.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-14).

Computes the Grobman 2007 logistic regression probability of vaginal birth after cesarean (VBAC) at the first prenatal visit using maternal age, prepregnancy BMI, ethnicity, and obstetric history flags

## Facts

- Endpoint: GET https://api.magentlab.com/api/calc/grobman_vbac
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/grobman-2007-vbac-probability-calculator-first-prenatal-visit-47b3f3e2
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_iqT-sDTijId4AzF24Ap1p

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability grobman-2007-vbac-probability-calculator-first-prenatal-visit-47b3f3e2
```

Example prompt: What's the Grobman 2007 first-prenatal-visit VBAC probability for a 34-year-old patient with a prepregnancy BMI of 28.5, ethnicity 'other', who has had a prior vaginal delivery, a prior VBAC, and whose prior cesarean was not for a recurrent indication?

## When to prefer this

Use this endpoint when you need the Grobman 2007 first-prenatal-visit VBAC probability specifically — not the 2009/2010 admission-time model and not the 2021 update. It is appropriate for prenatal counseling contexts where age, prepregnancy BMI, and obstetric history are known at the first visit. Prefer this over generic calculators when the clinical protocol explicitly references Grobman 2007 or when comparing against published first-prenatal-visit nomograms.

## Known failure modes

- Missing required query parameter (age, bmi_kg_m2, ethnicity, prior_vaginal, prior_vbac, or recurrent_indication) returns a 400/422 validation error
- Age outside clinical range 12–55 or BMI outside 15–70 may be rejected or flagged
- Invalid ethnicity value not in [african_american, hispanic, other] returns a validation error
- Payment not included or insufficient (x402 protocol) returns 402 Payment Required
- Non-integer age value returns a schema validation error

## How this service works

Grobman 2007 first prenatal visit logistic probability of vaginal birth after cesarean from maternal age, prepregnancy BMI, caller-assigned ethnicity (african_american, hispanic, or other), any prior vaginal delivery, prior VBAC after cesarean, and recurrent cesarean indication. Ethnicity uses the paper terms; magent does not assign race or ethnicity. Not the 2009/2010 admission model and not Grobman 2021. Not a trial-of-labor order.

## Output

Returns a numeric probability (0–1 logistic score) representing the predicted likelihood of achieving a vaginal birth after cesarean at the time of the first prenatal visit, derived from the Grobman 2007 regression coefficients applied to the supplied maternal age, prepregnancy BMI, ethnicity category, and three obstetric history boolean flags.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "headers": {
     "type": "object",
     "additionalProperties": {
      "type": "string"
     }
    },
    "queryParams": {
     "type": "object",
     "required": [
      "age",
      "bmi_kg_m2",
      "ethnicity",
      "prior_vaginal",
      "prior_vbac",
      "recurrent_indication"
     ],
     "properties": {
      "age": {
       "type": "integer",
       "description": "Maternal age in years (integer 12-55). Grobman 2007 coefficient -0.039 per year. 12-55 is a clinical range for TOLAC; the paper does not print that clamp. magent does not take a date of birth."
      },
      "bmi_kg_m2": {
       "type": "number",
       "description": "Prepregnancy BMI in kg/m^2 (15-70). Grobman 2007 coefficient -0.060. 15-70 is a clinical range; the paper does not print that clamp. Caller-supplied; magent does not compute BMI from height and weight."
      },
      "ethnicity": {
       "enum": [
        "african_american",
        "hispanic",
        "other"
       ],
       "type": "string",
       "description": "Caller-assigned ethnicity as used in Grobman 2007: african_american, hispanic, or other (mutually exclusive paper terms; other is the reference). magent does not assign race or ethnicity."
      },
      "prior_vbac": {
       "type": "boolean",
       "description": "VBAC after prior cesarean as assigned by the caller (Grobman 2007). true scores +1.003. true or false. magent does not infer this from prior_vaginal."
      },
      "prior_vaginal": {
       "type": "boolean",
       "description": "Any prior vaginal delivery as assigned by the caller (Grobman 2007). true scores +0.888. true or false. magent does not read the obstetric history."
      },
      "recurrent_indication": {
       "type": "boolean",
       "description": "Recurring indication for cesarean as assigned by the caller (Grobman 2007). true scores -0.632. true or false. magent does not read the operative indication."
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": 
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/grobman-2007-vbac-probability-calculator-first-prenatal-visit-47b3f3e2/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.magentlab.com](https://www.zero.xyz/host/api.magentlab.com/llms.txt)