ForHosting KIT · Developer Utilities

VBAC success calculator

Vaginal birth after cesarean (VBAC) is a trial of labor after a previous cesarean delivery, and families, midwives, educators, and product teams often need a transparent percentage that combines maternal age, body-mass index, ethnicity, whether there has been a prior vaginal birth, and whether the prior cesarean was for a recurring indication such as arrest of dilation. This VBAC success calculator estimates the probability of a successful vaginal birth after cesarean from those five required inputs using the Grobman 2007 Maternal-Fetal Medicine Units Network logistic model, returning a success probability percentage plus a counseling band. Any missing required field fails with invalid_input and is not billed. The same deterministic module powers the free browser widget and the API path, so teaching keys, research coding, and prototypes never disagree on a given vignette. Treat the JSON percentage as an educational arithmetic aid, not a diagnosis or a substitute for licensed obstetric judgment about trial of labor, uterine rupture counseling, or whether to schedule a repeat cesarean.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

How to use it

Enter your values in the form above. The tool checks them before calculating and shows the result on the same page.

Check your inputs

Use the labels and units shown next to each field. If something is missing or outside the allowed range, the page points to the field to fix.

Use it again or automate it

Use the browser tool for individual checks and the API when you need the same capability in an automated workflow.

What you can do with it

Get an answer now

Enter one set of values and see the result without building a spreadsheet or script.

Compare scenarios

Change one value at a time and rerun the calculation to understand what affects the result.

Automate repeated work

Use the API when the same calculation needs to run inside your product or workflow.

FAQ

What does this VBAC success calculator estimate?

It returns a predicted probability of successful vaginal birth after cesarean as success_pct (and the equivalent success_probability on 0–1) from maternal age, BMI, ethnicity, prior vaginal birth, and whether the prior cesarean indication was recurring.

Which formula does the calculator use?

The Grobman 2007 MFMU antepartum logistic model: logit = 3.766 − 0.039×age − 0.060×BMI − 0.671×African American − 0.680×Hispanic + 0.888×any prior vaginal delivery − 0.109×recurring indication, then P = 1/(1+e^(−logit)).

What counts as a recurring indication for the prior cesarean?

recurring covers arrest of dilation or descent, cephalopelvic disproportion, and failure to progress. non_recurring covers breech, fetal distress, previa, elective, and other non-dystocia indications. Unknown tokens fail with invalid_input.

How should I interpret high, moderate, and low predicted VBAC success?

Bands are educational cuts on success_pct: high is 70% or more, moderate is 50% up to 70%, and low is under 50%. They are counseling strata, not a personal prognosis or a delivery-route order.

Can I use this percentage to decide on a trial of labor?

No. This is an educational arithmetic aid, not medical advice. Trial of labor, uterine-rupture counseling, and whether to schedule a repeat cesarean need a licensed clinician and the rest of the clinical picture this calculator does not collect.

What does the VBAC success calculator cost?

The browser widget runs free and locally. The same computation via the API is billed at $0.002 per successful request from prepaid KIT balance; invalid_input failures are not charged.

For developers — API access

Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.

API endpoint

POSThttps://api.kit.forhosting.com/health/vbac-risk-score

Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.

Call it from your stack

curl -X POST https://api.kit.forhosting.com/health/vbac-risk-score \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"maternal_age":28,"bmi":24,"ethnicity":"white","prior_vaginal_birth":true,"prior_cesarean_indication":"non_recurring"}'

const res = await fetch("https://api.kit.forhosting.com/health/vbac-risk-score", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "maternal_age": 28,
    "bmi": 24,
    "ethnicity": "white",
    "prior_vaginal_birth": true,
    "prior_cesarean_indication": "non_recurring"
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/health/vbac-risk-score",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "maternal_age": 28,
    "bmi": 24,
    "ethnicity": "white",
    "prior_vaginal_birth": true,
    "prior_cesarean_indication": "non_recurring"
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/vbac-risk-score", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"maternal_age":28,"bmi":24,"ethnicity":"white","prior_vaginal_birth":true,"prior_cesarean_indication":"non_recurring"}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"maternal_age":28,"bmi":24,"ethnicity":"white","prior_vaginal_birth":true,"prior_cesarean_indication":"non_recurring"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/vbac-risk-score", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "maternal_age": 28,
  "bmi": 24,
  "ethnicity": "white",
  "prior_vaginal_birth": true,
  "prior_cesarean_indication": "non_recurring"
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "health.vbac_risk_score",
  "status": "queued",
  "_links": {
    "result": "/tasks/tsk_…/result"
  }
}

The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.

Pricing

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Limits

`min_age`	14
`max_age`	55
`min_bmi`	15
`max_bmi`	70

Errors

HTTP	Code	Meaning
`401`	`unauthorized`	Missing or invalid API key.
`402`	`insufficient_balance`	Your balance doesn't cover the task price.
`404`	`unknown_type`	That task type doesn't exist.
`429`	`rate_limited`	Too many requests. Use the webhook instead of polling.

Read the full KIT documentation →