Pregnancy Weight Gain: What's Recommended and Why It's a Range

Recommended weight gain in pregnancy depends on where you started. The guidelines from the Institute of Medicine — now the National Academy of Medicine — set different ranges according to pre-pregnancy BMI, because the outcomes they are designed to protect vary with starting weight.

Those outcomes are concrete: birth weight, the likelihood of complications during delivery, the risk of gestational diabetes and hypertensive disorders, and how much weight is retained afterwards. Both too little and too much gain are associated with worse results.

This article is general information rather than medical advice. Your maternity team's guidance, which accounts for your individual history, takes precedence over any published range.

For a singleton pregnancy, the IOM ranges by pre-pregnancy BMI are as follows. The Pregnancy Weight Gain Calculator works these out from your height and pre-pregnancy weight.

Carrying twins raises the recommended gain substantially, and the guidance is expressed with less precision because the evidence base is smaller.

For twins the IOM provisional ranges are roughly 17 to 25 kg (37 to 54 lb) for a normal pre-pregnancy BMI, 14 to 23 kg (31 to 50 lb) for overweight, and 11 to 19 kg (25 to 42 lb) for obese. No firm range was set for underweight women carrying twins, given limited data.

Multiple pregnancies carry higher risks generally and are monitored more closely. Weight gain targets in that context should come from your maternity team rather than from a general calculator.

It helps to know that most of the gain is not maternal fat. For a typical singleton pregnancy with around 12.5 kg of total gain, the approximate distribution is instructive.

Gain is not distributed evenly across the pregnancy, and expecting it to be causes unnecessary worry in the early months.

The first trimester typically brings very little — commonly 0.5 to 2 kg (1 to 4.5 lb) in total. Many people gain nothing at all, and some lose weight to nausea, which is usually not a concern.

The second and third trimesters carry most of it, at roughly 0.4 to 0.5 kg (about 1 lb) per week for someone with a normal pre-pregnancy BMI, scaled proportionally for other categories. The calculator compares your gain to date against the expected trajectory for your current week, which is more informative than comparing against the final total.

Mild weight loss in the first trimester is common and usually driven by nausea and vomiting. For most people it resolves as symptoms ease and requires no intervention beyond managing the symptoms.

It becomes worth raising with your maternity team if the loss is substantial, if it continues into the second trimester, or if you are unable to keep fluids down. Severe persistent vomiting — hyperemesis gravidarum — is a recognised condition that can require treatment.

The general principle: early loss is common, persistent loss should be discussed. Do not attempt to manage it by adjusting your diet without advice.

Gaining above the recommended range is associated with higher birth weight, a greater likelihood of caesarean delivery, and more weight retained after birth. Gaining below it is associated with low birth weight and preterm birth.

If your gain is running high, the response is not to diet. Deliberate weight loss is not advised during pregnancy, and restricting intake risks the nutrients the pregnancy depends on. The usual approach, under supervision, is to moderate the rate of gain through food quality and gentle activity rather than to reverse it.

If gain is running low, the emphasis is on nutrient-dense food and identifying anything interfering with intake. Either way this is a conversation to have with your maternity team rather than a problem to solve alone.

Weight loss after birth is immediate but partial. Delivery accounts for the baby, placenta and amniotic fluid — commonly 5 to 6 kg in total — and the following weeks bring a further reduction as excess fluid clears and the uterus contracts back toward its usual size.

What remains is largely the maternal fat laid down deliberately during pregnancy, much of it to support breastfeeding. Breastfeeding does draw on it, requiring roughly 450 to 500 extra calories a day, though its effect on weight loss varies considerably between individuals and is smaller than often claimed.

Most guidance suggests waiting until the postnatal check, usually around six weeks, before actively pursuing weight loss, and longer after a caesarean. Timelines vary enormously and there is no schedule anyone is obliged to meet.

'Eating for two' overstates the requirement considerably. Additional energy needs are commonly cited as roughly 340 extra calories a day in the second trimester and 450 in the third, with little or no increase in the first — well under a second full diet.

Nutrient quality matters more than quantity. Folate, iron, calcium, iodine, choline and omega-3 fats all carry increased requirements, and most maternity services recommend specific supplements. Follow the advice you are given locally, since recommendations vary by country.

Physical activity is generally encouraged in uncomplicated pregnancies, with guidance commonly suggesting around 150 minutes of moderate activity per week. Some activities are contraindicated, and some conditions require rest, so clear it with your maternity team first.