# Grobman 2007 first-visit VBAC

Grobman VBAC

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/grobman_vbac`
HTML: https://magentlab.com/docs/grobman-vbac
Markdown: https://magentlab.com/docs/grobman-vbac.md

Not a medical device. Not a diagnosis, dose, or listing recommendation.

## What it computes

Compute the Grobman 2007 first-prenatal-visit logistic probability of vaginal birth after cesarean from maternal age, prepregnancy BMI, caller-assigned ethnicity, any prior vaginal delivery, prior VBAC after cesarean, and recurrent cesarean indication.

## When to use

When an agent already has Grobman 2007 first-visit predictors and needs that paper's probability. Not a trial-of-labor order, not the Flamm admission score, not the 2009/2010 admission model, and not Grobman 2021.

## When not to use

- Not a medical device and not a trial-of-labor or cesarean order.
- ethnicity is caller-assigned as african_american, hispanic, or other using Grobman 2007 terms. magent does not assign race or ethnicity.
- Grobman 2007 first prenatal visit logistic model only. Not the 2009/2010 admission or intrapartum model. A later MFMU model without race/ethnicity exists (Grobman 2021) and is not this tool.
- Age 12-55 and BMI 15-70 are clinical ranges for TOLAC. Grobman 2007 does not print those clamps.
- prior_vaginal, prior_vbac, and recurrent_indication are caller-assigned independently. magent does not infer obstetric history.

## Formula

```
w = 3.766 - 0.039*age_years - 0.060*prepregnancy_bmi - 0.671*[african_american] - 0.680*[hispanic] + 0.888*[any prior vaginal delivery] + 1.003*[VBAC after prior cesarean] - 0.632*[recurring indication for cesarean]; vbac_probability = exp(w)/(1+exp(w)); ethnicity african_american|hispanic|other (caller-assigned Grobman 2007 terms, mutually exclusive; other is the reference; magent does not assign race or ethnicity); flags 1 if true else 0; first prenatal visit model; round linear_predictor and vbac_probability 3 decimals; not Grobman 2009/2010 admission; not Grobman 2021 race-free; not a TOLAC order
```

## Citation

[Development of a nomogram for prediction of vaginal birth after cesarean delivery](https://doi.org/10.1097/01.AOG.0000259312.36053.02)
Grobman WA, Lai Y, Landon MB, Spong CY, Leveno KJ, Rouse DJ, Varner MW, Moawad AH, Caritis SN, Harper M, Wapner RJ, Sorokin Y, Miodovnik M, Carpenter M, Peaceman AM, O'Sullivan MJ, Sibai BM, Langer O, Thorp JM, Ramin SM, Mercer BM; National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units Network (MFMU)
Obstet Gynecol. 2007;109(4):806-812
DOI: [10.1097/01.AOG.0000259312.36053.02](https://doi.org/10.1097/01.AOG.0000259312.36053.02)

## Worked example

### Age 30, BMI 25, ethnicity other, all flags false

Given: `age=30, bmi_kg_m2=25, ethnicity=other, prior_vaginal=false, prior_vbac=false, recurrent_indication=false`

1. ethnicity other → African American 0, Hispanic 0; prior_vaginal false → 0; prior_vbac false → 0; recurrent_indication false → 0
2. w = 3.766 - 0.039×30 - 0.060×25 = 1.096
3. vbac_probability = exp(1.096)/(1+exp(1.096))


### Same inputs, african_american (published coefficient)

Given: `age=30, bmi_kg_m2=25, ethnicity=african_american, prior_vaginal=false, prior_vbac=false, recurrent_indication=false`

1. african_american subtracts 0.671 from the other-ethnicity logit
2. w = 1.096 - 0.671 = 0.425; caller assigns ethnicity; magent does not assign race


### Same inputs, hispanic (published coefficient)

Given: `age=30, bmi_kg_m2=25, ethnicity=hispanic, prior_vaginal=false, prior_vbac=false, recurrent_indication=false`

1. hispanic subtracts 0.680 from the other-ethnicity logit
2. w = 1.096 - 0.680 = 0.416; caller assigns ethnicity; magent does not assign race


### Same other-ethnicity row, any prior vaginal delivery

Given: `age=30, bmi_kg_m2=25, ethnicity=other, prior_vaginal=true, prior_vbac=false, recurrent_indication=false`

1. prior_vaginal true adds 0.888 to the logit
2. w = 1.096 + 0.888 = 1.984


## Also searched as

- Grobman VBAC
- Grobman 2007 nomogram
- first prenatal visit VBAC
- MFMU VBAC prediction
- vaginal birth after cesarean probability
- TOLAC success probability
- Grobman first visit model
- NICHD MFMU VBAC

## Parameters

- `age` (integer, required): 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` (number, required): 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` (string, required): 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_vaginal` (boolean, required): 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.
- `prior_vbac` (boolean, required): 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.
- `recurrent_indication` (boolean, required): 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.

## Bulk (POST)

POST the same path with a JSON items array. The first item is the GET unit; each additional item is $0.002. Invalid items return HTTP 400 before settlement.

Method: `POST /api/calc/grobman_vbac`
Max items: 25
Price: unit_amount + extra_item_amount * (n - 1) (unit 5000 atomic, extra 2000 atomic)
Status: PREVIEW

- 1 to 25 items. Each item uses the same keys as the GET query parameters.
- POST of 1 item costs the same as GET. Lists longer than 25: chunk into multiple POSTs. Extra items still execute; do not pad dummy rows.
- The first invalid item fails the whole request (index in the 400 JSON). You are not charged.
- HTTP 200 is {count, path, items}. Each items[i] is the GET 200 body for that row.
- Catalog misses (empty matches, found=false) stay paid 200s inside that slot.
- x402 resource URL is this path plus n and body_sha256. Browsers that prefer text/html get the same paywall as GET; Pay retries POST with the same items.

Example request:

```json
{
  "items": [
    {
      "age": "30",
      "bmi_kg_m2": "25",
      "ethnicity": "other",
      "prior_vaginal": "false",
      "prior_vbac": "false",
      "recurrent_indication": "false"
    },
    {
      "age": "30",
      "bmi_kg_m2": "25",
      "ethnicity": "other",
      "prior_vaginal": "false",
      "prior_vbac": "false",
      "recurrent_indication": "false"
    }
  ]
}
```

Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/grobman-vbac

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/grobman_vbac",
  "items": [
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Grobman WA, Lai Y, Landon MB, Spong CY, Leveno KJ, Rouse DJ, Varner MW, Moawad AH, Caritis SN, Harper M, Wapner RJ, Sorokin Y, Miodovnik M, Carpenter M, Peaceman AM, O'Sullivan MJ, Sibai BM, Langer O, Thorp JM, Ramin SM, Mercer BM; National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units Network (MFMU)",
        "doi": "10.1097/01.AOG.0000259312.36053.02",
        "id": "grobman-2007-vbac",
        "pmid": "17400840",
        "source": "Obstet Gynecol. 2007;109(4):806-812",
        "title": "Development of a nomogram for prediction of vaginal birth after cesarean delivery"
      },
      "formula": "grobman_vbac",
      "formula_expression": "w = 3.766 - 0.039*age_years - 0.060*prepregnancy_bmi - 0.671*[african_american] - 0.680*[hispanic] + 0.888*[any prior vaginal delivery] + 1.003*[VBAC after prior cesarean] - 0.632*[recurring indication for cesarean]; vbac_probability = exp(w)/(1+exp(w)); ethnicity african_american|hispanic|other (caller-assigned Grobman 2007 terms, mutually exclusive; other is the reference; magent does not assign race or ethnicity); flags 1 if true else 0; first prenatal visit model; round linear_predictor and vbac_probability 3 decimals; not Grobman 2009/2010 admission; not Grobman 2021 race-free; not a TOLAC order",
      "age_years": 30,
      "bmi_kg_m2": 25.0,
      "linear_predictor": 1.096,
      "ethnicity": "other",
      "prior_vaginal": false,
      "prior_vbac": false,
      "recurrent_indication": false,
      "vbac_probability": 0.75
    },
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Grobman WA, Lai Y, Landon MB, Spong CY, Leveno KJ, Rouse DJ, Varner MW, Moawad AH, Caritis SN, Harper M, Wapner RJ, Sorokin Y, Miodovnik M, Carpenter M, Peaceman AM, O'Sullivan MJ, Sibai BM, Langer O, Thorp JM, Ramin SM, Mercer BM; National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units Network (MFMU)",
        "doi": "10.1097/01.AOG.0000259312.36053.02",
        "id": "grobman-2007-vbac",
        "pmid": "17400840",
        "source": "Obstet Gynecol. 2007;109(4):806-812",
        "title": "Development of a nomogram for prediction of vaginal birth after cesarean delivery"
      },
      "formula": "grobman_vbac",
      "formula_expression": "w = 3.766 - 0.039*age_years - 0.060*prepregnancy_bmi - 0.671*[african_american] - 0.680*[hispanic] + 0.888*[any prior vaginal delivery] + 1.003*[VBAC after prior cesarean] - 0.632*[recurring indication for cesarean]; vbac_probability = exp(w)/(1+exp(w)); ethnicity african_american|hispanic|other (caller-assigned Grobman 2007 terms, mutually exclusive; other is the reference; magent does not assign race or ethnicity); flags 1 if true else 0; first prenatal visit model; round linear_predictor and vbac_probability 3 decimals; not Grobman 2009/2010 admission; not Grobman 2021 race-free; not a TOLAC order",
      "age_years": 30,
      "bmi_kg_m2": 25.0,
      "linear_predictor": 1.096,
      "ethnicity": "other",
      "prior_vaginal": false,
      "prior_vbac": false,
      "recurrent_indication": false,
      "vbac_probability": 0.75
    }
  ]
}
```

## Response fields

- `formula` (string): grobman_vbac
- `formula_expression` (string): Grobman 2007 first prenatal visit logistic expression
- `age_years` (integer): Maternal age in years used (12-55)
- `bmi_kg_m2` (number): Prepregnancy BMI in kg/m^2 used (15-70)
- `ethnicity` (string): Caller-assigned african_american, hispanic, or other used
- `prior_vaginal` (boolean): Caller-assigned any prior vaginal delivery used
- `prior_vbac` (boolean): Caller-assigned VBAC after prior cesarean used
- `recurrent_indication` (boolean): Caller-assigned recurring cesarean indication used
- `linear_predictor` (number): Grobman 2007 logit w, 3 decimals
- `vbac_probability` (number): exp(w)/(1+exp(w)) on 0-1, 3 decimals. A published probability, not a counseling band or trial-of-labor order.
- `citation` (object): Grobman et al. Obstet Gynecol 2007 citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
  "citation": {
    "authors": "Grobman WA, Lai Y, Landon MB, Spong CY, Leveno KJ, Rouse DJ, Varner MW, Moawad AH, Caritis SN, Harper M, Wapner RJ, Sorokin Y, Miodovnik M, Carpenter M, Peaceman AM, O'Sullivan MJ, Sibai BM, Langer O, Thorp JM, Ramin SM, Mercer BM; National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units Network (MFMU)",
    "doi": "10.1097/01.AOG.0000259312.36053.02",
    "id": "grobman-2007-vbac",
    "pmid": "17400840",
    "source": "Obstet Gynecol. 2007;109(4):806-812",
    "title": "Development of a nomogram for prediction of vaginal birth after cesarean delivery"
  },
  "formula": "grobman_vbac",
  "formula_expression": "w = 3.766 - 0.039*age_years - 0.060*prepregnancy_bmi - 0.671*[african_american] - 0.680*[hispanic] + 0.888*[any prior vaginal delivery] + 1.003*[VBAC after prior cesarean] - 0.632*[recurring indication for cesarean]; vbac_probability = exp(w)/(1+exp(w)); ethnicity african_american|hispanic|other (caller-assigned Grobman 2007 terms, mutually exclusive; other is the reference; magent does not assign race or ethnicity); flags 1 if true else 0; first prenatal visit model; round linear_predictor and vbac_probability 3 decimals; not Grobman 2009/2010 admission; not Grobman 2021 race-free; not a TOLAC order",
  "age_years": 30,
  "bmi_kg_m2": 25.0,
  "linear_predictor": 1.096,
  "ethnicity": "other",
  "prior_vaginal": false,
  "prior_vbac": false,
  "recurrent_indication": false,
  "vbac_probability": 0.75
}
```

## Errors

- HTTP 400 `invalid_grobman_vbac`: Grobman 2007 first-visit VBAC inputs must match age, BMI, caller-assigned ethnicity, prior vaginal birth, prior VBAC, and recurrent cesarean indication. Returned before settlement; you are not charged.
- HTTP 400 `invalid_flag`: boolean clinical flags must be true or false Returned before settlement; you are not charged.
- HTTP 400 `invalid_items`: POST body must be a JSON object with only an items array Returned before settlement; you are not charged.
- HTTP 400 `invalid_item_count`: items must be an array of 1 to 25 objects Returned before settlement; you are not charged.
- HTTP 400 `invalid_item`: each items entry must be a JSON object Returned before settlement; you are not charged.

Shared HTTP 402 and 503: https://magentlab.com/docs/payments

## Related tools

- [Flamm VBAC score](https://magentlab.com/docs/flamm-vbac) — Sum the Flamm 1997 admission VBAC points (max 10) from caller-assigned age, vaginal-birth history, first-cesarean indication, and admission cervical factors, and return the published 49% or 95% success rates only for scores 0–2 and 8–10.
- [simplified Bishop score](https://magentlab.com/docs/simplified-bishop) — Return the Laughon 2011 simplified Bishop score as the sum of three caller-assigned Bishop 1964 integers (dilation, station, effacement; each 0-3; max 9) and whether the score is >5.
- [Bishop score](https://magentlab.com/docs/bishop) — Return the Bishop 1964 pelvic score as the sum of five caller-assigned integer components (dilation, effacement, station, consistency, position).

## Payment

Unpaid requests return HTTP 402 even if query parameters or POST items are missing or invalid, so CDP and agents can index the path. After a PAYMENT-SIGNATURE, invalid params return HTTP 400 JSON before settlement. magent does not charge. Fix the params, then request a new 402 quote for that complete URL. Catalog misses (empty matches, found=false) are valid paid 200s.

- GET the tool with Accept: application/json (do not send Accept: text/html unless you want the human paywall).
- HTTP 402 means you have not paid. Decode the base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote.
- Sign accepts[0] (exact, EIP-3009) with validBefore = now + maxTimeoutSeconds (600 seconds), or accepts[1] (batch-settlement deposit/voucher) on product GET. Ping and POST {items} stay exact. Magent retries transient facilitator 429/5xx before answering.
- Retry the same URL with PAYMENT-SIGNATURE (base64 JSON of accepted and payload). Magent attaches canonical extensions.bazaar on CDP verify/settle; echoing 402 bazaar is optional.
- Success is HTTP 200 JSON plus PAYMENT-RESPONSE. exact settles before the tool. batch-settlement verifies (and deposit-settles) before the tool and commits the charge after HTTP 2xx. HTTP 503: retry the same PAYMENT-SIGNATURE. Mint a new exact nonce only after a new HTTP 402.

- offered `exact` on eip155:8453: Fixed-price USDC on Base. The buyer authorizes the advertised amount (EIP-3009). magent settles before the tool runs (paymentFlow upfront). extra.assetTransferMethod=eip3009 extra.paymentFlow=upfront.
- offered `batch-settlement` on eip155:8453: Payment-channel vouchers claimed later in batches. Exact stays accepts[0]. Same-path POST {items} is still exact. extra.assetTransferMethod=eip3009 extra.paymentFlow=authorization.

- not offered `upto`: Not offered. Usage-based: buyer authorizes a ceiling, seller settles the actual amount after work. Reserved for a future metered tool. Not for current calculators or code search.

Same-path POST {items} is still scheme exact: one EIP-3009 authorization for GET unit plus $0.002 per extra item. That is not x402 batch-settlement (payment channels / vouchers).

Shared HTTP 402 and 503 table: https://magentlab.com/docs/payments

Stdio MCP (one process per host): https://magentlab.com/docs/mcp

## Guarantees

- HTTP 402 is unpaid, including a missing query. After PAYMENT-SIGNATURE, invalid parameters return HTTP 400 before settlement. You are not charged. HTTP 402 never includes the tool JSON.
- exact: settlement finishes before the tool (paymentFlow upfront). batch-settlement: verify/deposit before the tool; chargedCumulativeAmount commits after HTTP 2xx. Uncertain or failed settlement fails closed (HTTP 503). Retry the same PAYMENT-SIGNATURE.
- HTTP 402 is unpaid only. Do not sign a second authorization because of a 503.
- Execution is timeout-bounded and concurrency-capped.
- Calculator inputs are stored encrypted for allowlisted operators (Magent Console). They are not in public logs, SSH lookups, catalog, or rollups. Request logs store path without query.