Twin pregnancy weight gain calculator

BMI that is missing, zero, negative, or not a finite number is rejected with invalid_input so a nonsense index never invents a schedule.

How to call the API and what comes back

Fractional weeks are accepted for mid-week checks. Failed validation is never charged. Send a JSON body with two required finite numbers: bmi (aliases pre_pregnancy_bmi, prepregnancy_bmi, bmi_pre, pre_bmi) and weeks (aliases gestation_weeks, gestational_weeks, week, ga_weeks). Pre-pregnancy BMI must be a positive number; zero, negative, missing, or non-finite values return invalid_input naming that field. Gestational weeks must be at least zero and at most forty-two; any value strictly greater than forty-two also returns invalid_input. On success the response echoes rounded bmi and weeks, sets bmi_category to underweight, normal, overweight, or obese, category_label to a human English band name, guideline to IOM/NRC 2009 twin, pregnancy_type to twin, gain_min_kg and gain_max_kg to the cumulative recommended range at that week, gain_min_lb and gain_max_lb as pound equivalents, total_recommended_min_kg and total_recommended_max_kg for twin-term totals with matching pound fields, weekly_rate_min_kg and weekly_rate_max_kg for the second- and third-trimester rates, first_trimester_min_kg and first_trimester_max_kg for the derived week-thirteen endpoints, unit_primary as kg, message as a short English summary, and steps as an ordered array of classification and interpolation lines. Pricing is a flat $0.002 per successful request with unit item and zero marginal unit price. Prefer this endpoint when you already have pre-pregnancy BMI and gestational age and only need the published twin kilogram range; if your source is height and weight, compute BMI first, then call this calculator.

Practical tips, limits, and related searches

Use true pre-pregnancy BMI, not a mid-pregnancy BMI, when selecting the band; mixing current weight into the BMI field will misclassify the guideline row and shift both the weekly rate and the twin-term total. Prefer numbers rather than pre-formatted strings when you control the client; string numbers are accepted only when they match a strict finite numeric pattern. Prefer this capability when the pregnancy is a twin gestation and you already have pre-pregnancy BMI and gestational age; singleton schedules use a different published table and a forty-week horizon. When teaching, pair examples: BMI twenty-two at twenty weeks (normal band, mid-pregnancy cumulative range), BMI thirty-two at thirty-seven weeks (obese band at twin term, where cumulative gain matches the published eleven point three to nineteen point one kilogram totals), BMI seventeen at twelve weeks (underweight first-trimester ramp), and deliberate BMI zero or a negative BMI to demonstrate the hard invalid_input path for a non-positive index. This landing targets people searching for a twin pregnancy weight gain calculator, IOM twin gestational weight gain by BMI, or recommended weight gain for twins by week; it is not a singleton pregnancy weight-gain table, not a BMI calculator from height and weight, not a calorie planner, and not medical advice. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when learners deliberately send a non-positive BMI. Round-trip checks are easy: confirm the BMI category matches WHO cut-points, confirm twin-term totals match the IOM (or provisional underweight) table for that band, and at week thirty-seven confirm cumulative gain_min_kg and gain_max_kg equal the published totals within the same twelve-decimal rounding.