Weight Gain During Pregnancy: What's Normal and What to Expect

Weight gain during pregnancy is normal, necessary, and healthy. The growing baby, placenta, amniotic fluid, increased blood volume, and breast tissue changes all contribute to weight gain that has nothing to do with “extra” body fat. Trying to avoid weight gain during pregnancy is not only unnecessary but can be harmful. At the same time, significant excess weight gain is associated with complications. The goal is a middle path: eating well to support the pregnancy without either restricting or significantly overeating.

Why Weight Gain Matters

Weight gain during pregnancy supports:

• Fetal growth and development
• The placenta (which weighs around 600–700g at term)
• Amniotic fluid
• Increased blood volume (around 1.5 litres extra by late pregnancy)
• Uterine growth
• Breast tissue preparation for feeding
• Fat stores that support breastfeeding after birth

These components together account for 8–12kg of weight gain in a typical pregnancy, even with relatively modest fat accumulation.

What Are the Recommended Ranges?

In the UK, the NHS does not publish strict weight gain targets for individual pregnancies in the way some other countries do. This is because healthy weight gain varies considerably depending on your starting weight (BMI), whether you are carrying twins, your height, and other factors. However, general guidance from international bodies including the Institute of Medicine is widely used as a reference:

Pre-pregnancy BMI	Recommended total gain
Underweight (BMI under 18.5)	12.5–18 kg
Healthy weight (BMI 18.5–24.9)	11.5–16 kg
Overweight (BMI 25–29.9)	7–11.5 kg
Obese (BMI 30+)	5–9 kg

For twin pregnancies, the ranges are higher.

These are reference ranges, not targets to hit precisely. Individual variation is large and normal. What matters more than a specific number is eating a nutrient-dense diet, attending your midwife appointments, and flagging concerns about either very slow or very rapid weight gain to your healthcare team.

When Does Weight Gain Happen?

The pattern of weight gain is not linear:

• First trimester: Very little weight gain is typical — often 1–2kg total, and some women lose weight due to nausea and vomiting. The baby is very small at this stage and weight gain is mostly maternal tissue changes.

• Second trimester: Weight gain typically accelerates to around 0.3–0.5kg per week as the baby grows faster and blood volume expands.

• Third trimester: Similar rate to the second trimester, or slightly less toward the end as the baby drops lower and appetite can decrease as the stomach is compressed.

Eating for Two: The Reality

“Eating for two” is one of the most misleading pieces of pregnancy advice. The energy increase required in pregnancy is:

• First trimester: No increase needed
• Second trimester: Approximately 300 extra calories per day
• Third trimester: Approximately 300–500 extra calories per day

That is roughly the equivalent of an extra bowl of porridge with fruit, or a peanut butter sandwich and a piece of fruit. The “extra” is modest. What changes more than quantity is the importance of quality — making the extra food nutrient-dense rather than adding empty calories.

Hunger increases during pregnancy, and following your appetite is appropriate. But if appetite is significantly outpacing these rough estimates — eating several extra large meals per day — it is worth discussing with your midwife, as it can lead to excess gain that creates complications.

What Does Excess Weight Gain Risk?

Gaining significantly more than the recommended range increases risk of:

• Gestational diabetes
• Pre-eclampsia (high blood pressure in pregnancy)
• Larger-than-average baby (macrosomia), which can complicate delivery
• Emergency caesarean
• Difficulty losing weight after birth

It does not mean these things will happen — it means the statistical risk is modestly elevated.

What Does Inadequate Weight Gain Risk?

Gaining less than recommended (particularly if you start in a healthy BMI range) is associated with:

• Low birth weight and growth restriction
• Preterm birth
• Increased risk of the baby having developmental difficulties

Practical Eating Guidance

Don’t diet during pregnancy. This is not the time to restrict calories, skip meals, or eliminate food groups in the name of weight management. Nutrient shortfalls during pregnancy affect fetal development. If your pre-pregnancy weight means your team wants to discuss weight management, this should be a guided conversation with your midwife and ideally a registered dietitian — not something to approach alone.

Focus on food quality over quantity. Building meals around vegetables, protein, whole grains, dairy (or fortified alternatives), and healthy fats means you are likely to feel full, eat well, and not excessively overconsume.

Follow your hunger. Pregnancy hunger is real and legitimate. Trying to ignore significant hunger during pregnancy can lead to over-compensatory eating and stress. Eating when hungry, stopping when full, and choosing mostly nutritious foods is a more sustainable approach than tracking calories.

Watch added sugars and processed foods. Soft drinks, confectionery, crisps, and highly processed foods add calories and very little nutritional value. Reducing these (rather than reducing fruit, vegetables, or whole foods) is the most sensible way to moderate caloric intake if it is a concern.

Move as much as you comfortably can. Regular moderate exercise — walking, swimming, pregnancy yoga — supports healthy weight management, mood, sleep, and preparation for labour without risk to the pregnancy. See the Exercise section of this site for guidance.

The Scales and Your Mental Wellbeing

Some women find it helpful to weigh themselves periodically during pregnancy; others find it a source of anxiety. The NHS does not routinely weigh pregnant women at every midwife appointment, partly because weight alone is not a reliable indicator of pregnancy health and partly because it can fuel unhealthy preoccupations. Your midwife will measure fundal height (the height of the uterus) as a proxy for fetal growth, which is more directly relevant.

If weight gain — too fast, too slow, or the concept of weight gain in general — is causing significant anxiety, speak to your midwife. This is common, particularly for women with a history of disordered eating, and there is support available. A referral to a perinatal dietitian or a specialist midwife can make a real difference.

The goal of pregnancy nutrition is to grow a healthy baby and take good care of yourself — not to hit a number on a scale. Keeping that the focus makes it easier to approach eating during pregnancy with the calm and balance it deserves.