Pregnancy Weight Gain: How Much by BMI, by Trimester and With Twins

How much weight should you gain during pregnancy?

The recommended gain depends on your body mass index (BMI) before pregnancy. The Institute of Medicine's 2009 guidelines, which the CDC publishes, recommend 25 to 35 pounds (11.5 to 16 kg) for one baby if your BMI was 18.5 to 24.9, more if it was lower and less if it was higher.

Each BMI group gets a range. The Institute of Medicine says the ranges reflect how imprecise the underlying estimates are, that good outcomes are achieved within a range of weight gains, and that many other factors may need to be considered for an individual woman.

The CDC's list labels the highest group as a BMI of 30.0 to 39.9. ACOG (the American College of Obstetricians and Gynecologists) notes that BMI is one tool for describing weight categories and does not account for body composition or other factors.

How much weight should you gain each trimester?

The US guidance allows for a small gain in the first trimester and gives weekly rates for the second and third. ACOG says that in the first 12 weeks you may gain only 1 to 5 pounds (0.5 to 2.3 kg) or no weight at all, and the Institute of Medicine's weekly figures assume a first-trimester gain of 1.1 to 4.4 pounds (0.5 to 2 kg).

From the second trimester on, the weekly rates in the table apply. ACOG's own summary puts it as half a pound to 1 pound (0.23 to 0.45 kg) a week if you were a healthy weight before pregnancy, and a little under half a pound a week for women with obesity. If nausea and vomiting mean you are losing weight early on, morning sickness covers what helps and when to call.

The CDC and ACOG say the first trimester usually needs no extra calories, the second about 340 extra calories a day, and the third about 450; ACOG gives these figures for women who started pregnancy at a healthy weight. The NHS gives a lower figure: it says you can add another 200 calories a day when you enter the third trimester in week 28.

How much weight should you gain with twins?

With twins, the CDC recommends 37 to 54 pounds (17 to 25 kg) if your BMI was 18.5 to 24.9 before pregnancy. Its full list:

• BMI under 18.5: 50 to 62 lb (23 to 28 kg)
• BMI 18.5 to 24.9: 37 to 54 lb (17 to 25 kg)
• BMI 25.0 to 29.9: 31 to 50 lb (14 to 23 kg)
• BMI 30.0 to 39.9: 25 to 42 lb (11 to 19 kg)

The Institute of Medicine called its twin figures provisional, and it found too little information to set even a provisional range for underweight women carrying more than one baby. The CDC's underweight figure for twins comes from a separate source. For triplets or more, the CDC says to talk with your health care provider about your weight gain goals.

What does the NHS say about weight gain in pregnancy?

The NHS does not give target ranges. It says weight gain in pregnancy varies greatly, and that most pregnant women gain between 10 and 12.5 kg (22 to 28 lb), putting on most of it after week 20. Much of that is the baby growing, and your body also stores fat ready to make breast milk.

NICE (the National Institute for Health and Care Excellence) says there is a lack of evidence about what the optimal total weight change in pregnancy, or the change in each trimester, should be. It advises against routinely weighing people throughout pregnancy unless there is a clinical reason, such as gestational diabetes. If you want to track your weight, NICE points to a table of estimated healthy total weight change for one baby, by pre-pregnancy BMI, from the US National Academy of Medicine.

The NHS adds that your midwife or GP may have special advice for you if your BMI is over 30 or below 18.5.

What if your weight gain is above or below the range?

Talk it through with your doctor or midwife; being outside the range is common. The CDC reports that in one study only about 1 in 3 women gained the recommended amount, about 1 in 5 gained less and about 1 in 2 gained more.

ACOG says that if your weight gain is higher or lower than these averages, you and your ob-gyn can make a plan that fits your needs, and that everyone has a right to respectful care delivered without judgment, whatever their weight. The Institute of Medicine asks clinicians to consider what might be causing the difference, whether extra weight is fat or fluid, and whether the baby is growing adequately and steadily before suggesting any change.

The NHS says that gaining a lot or very little can both lead to health problems. Its list for a large gain includes gestational diabetes and pre-eclampsia; for a small gain, premature birth and a baby with a low birth weight (under 2.5 kg, or 5.5 lb). It also notes that some naturally slim women stay slim while they are pregnant and have healthy babies.

The NHS says pregnancy isn't the time to go on a diet, as it may harm the health of the unborn child, and NICE says intentional weight loss during pregnancy is not recommended because of potential adverse effects on the baby.

When should you call your doctor or midwife?

• Any of the preeclampsia symptoms ACOG lists: sudden weight gain, swelling of the face or hands, a headache that will not go away, seeing spots or changes in eyesight, pain in the upper abdomen or shoulder, nausea and vomiting in the second half of pregnancy, or difficulty breathing. ACOG says to call right away, especially if they start in the second half of pregnancy.
• Any worry about your weight. The NHS says to ask your midwife or GP for advice if you are concerned about your weight or any other aspect of your health while pregnant.