Recommended gain by week for twin pregnancies (IOM guideline ranges)
| Pre-pregnancy BMI | Total Gain (lb) | Total Gain (kg) |
|---|---|---|
| Underweight (< 18.5) | No IOM guideline — follow your OB | |
| Normal (18.5–24.9) | 37 – 54 | 17 – 25 |
| Overweight (25–29.9) | 31 – 50 | 14 – 23 |
| Obese (≥ 30) | 25 – 42 | 11 – 19 |
| Week | Recommended Cumulative Gain (lb) | Overweight BMI (lb) | Obese BMI (lb) |
|---|---|---|---|
| 12 | 1 – 4 | 1 – 4 | 1 – 4 |
| 16 | 11 – 16 | 9 – 15 | 8 – 12 |
| 20 | 18.5 – 27 | 15.5 – 25 | 12.5 – 21 |
| 24 | 22 – 32 | 18.5 – 30 | 15 – 25 |
| 28 | 26 – 38 | 22 – 35 | 17.5 – 29.5 |
| 32 | 29.5 – 43 | 25 – 40 | 20 – 33.5 |
| 36 | 33 – 48.5 | 28 – 45 | 22.5 – 38 |
| 38–40 (delivery) | 37 – 54 | 31 – 50 | 25 – 42 |
Week-by-week figures scale the IOM totals across a 40-week frame, weighted toward earlier weeks because twins deliver early. Treat them as pace markers, not grades; twin care leans on ultrasound growth, not the scale.
Twins change the math everywhere: more total gain, a faster weekly pace, and a shorter runway, since most twin deliveries land around 36 to 37 weeks. The IOM ranges above are the ones most US obstetricians reference, and the week-by-week table translates them into cumulative targets you can check at appointments.
A worked example: at 5'4" and 130 lb before pregnancy, BMI is 22.3 (703 × 130 ÷ 64²), squarely normal, so the twin target is 37–54 lb. At week 28 the table calls for roughly 26–38 lb, and the pace from here is about 1.5 lb a week, more than double a singleton's. If the number at the appointment is well under the low end, that's a nutrition conversation to have early, not late.
For the singleton version of this math, or to check an on-track status against your exact BMI, use the main pregnancy weight gain calculator. For timeline questions, our due date calculator and BMI calculator cover the neighbors of this question.
37 to 54 pounds if you started at a normal BMI, 31 to 50 if overweight, and 25 to 42 with obesity, per the 2009 IOM guidelines. The IOM publishes no twin range for underweight pregnancies because the data were insufficient; those are managed individually by the obstetrician.
Two babies, two placentas (or one large one), roughly double the amniotic fluid, and a much larger uterus and blood-volume increase. At term the twin-specific hardware alone can account for 25-plus pounds before any maternal stores.
Faster than a singleton: commonly cited at around 1.5 pounds a week after the first trimester at normal BMI, with the biggest needs in the second trimester, since twins deliver early on average (around 36 to 37 weeks) and much of the gain has to be banked before then.
Around 36 to 37 weeks on average, and planned deliveries are often scheduled for 38 weeks or earlier. That's why the week-by-week targets above steepen earlier than singleton charts: the runway is shorter.