The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
Weight Loss In The First Trimester — What You Need To Know
Weight loss during the first trimester of pregnancy is not recommended and should be avoided. If you're experiencing unintended weight loss during early pregnancy, this may indicate a medical concern that requires attention from your GP or midwife. The first trimester is a critical period of foetal development, and your body needs adequate nutrition to support this growth. Rather than focusing on weight loss, the NHS advises pregnant women to prioritise balanced nutrition and regular antenatal care. If you have concerns about your weight or are struggling with morning sickness affecting your diet, speak to your midwife immediately.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Why Weight Loss In Early Pregnancy Is Unsafe
Intentional weight loss during the first trimester can harm foetal development and increase miscarriage risk. Your body requires additional nutrients — including protein, iron, folate, and calcium — to support your baby's organ formation and your own physiological changes. Weight loss at this critical stage may deprive your baby of essential nutrients.
Normal weight changes in the first trimester:
- Many women lose weight due to morning sickness and nausea — this is not intentional weight loss and usually resolves by week 12
- Some women gain 1–2 kg in the first trimester; others maintain their weight
- Individual variation is normal; your midwife will monitor your weight trends
If you're losing weight unintentionally or experiencing severe nausea, inform your midwife immediately. She can offer practical support and ensure you're receiving adequate nutrition for your baby's development.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
When To Seek Medical Support
Contact your GP or midwife if you're experiencing persistent unintended weight loss, severe morning sickness lasting beyond week 12, inability to keep food down, or dizziness and fatigue. These symptoms may indicate hyperemesis gravidarum (severe pregnancy sickness) or other pregnancy complications requiring treatment.
Weight management discussions during pregnancy should always involve your healthcare team, not external weight loss programmes. Your GP and midwife understand the unique nutritional demands of pregnancy and can offer safe, personalised guidance. The NHS Weight Loss Plan and similar general programmes are not appropriate during pregnancy. Focus instead on eating regular, balanced meals with plenty of fruits, vegetables, whole grains, lean protein, and dairy — and on attending all your antenatal appointments.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Is it safe to use weight loss injections during the first trimester?
No. Weight loss medications, including GLP-1 injections like Wegovy, are absolutely contraindicated in pregnancy. These medications have not been tested in pregnant women and may harm foetal development. You must inform your prescriber if you become pregnant or plan to become pregnant. If you're taking any weight loss medication and discover you're pregnant, stop immediately and contact your GP.
Will I gain weight during pregnancy if I don't diet?
Most women naturally gain weight during pregnancy — the NHS recommends a total gain of 10–12.5 kg over all nine months for those starting at a healthy weight. This weight supports your baby, placenta, increased blood volume, and breast tissue. Weight gain is healthy and necessary. Avoid calorie restriction; focus on nutritious foods instead.
What should I eat to stay healthy in the first trimester?
Eat regular, balanced meals including lean protein, wholegrains, fruits, vegetables, and dairy. Prenatal vitamins with folic acid are essential. If morning sickness affects your appetite, eat smaller, frequent meals and stay hydrated. Your midwife or a pregnancy dietitian can provide personalised guidance on nutrition during your first trimester.
Is it normal to lose weight in early pregnancy due to morning sickness?
Yes, many pregnant women lose 1–2 kg in the first trimester due to nausea and vomiting. This usually resolves by week 12. While this weight loss is unintentional and generally not harmful if temporary, persistent severe sickness (hyperemesis gravidarum) requires medical treatment. Always inform your midwife about morning sickness severity.
Can I use the NHS Weight Loss Plan during pregnancy?
No. The NHS Weight Loss Plan and all weight loss programmes are unsuitable during pregnancy. Your healthcare team will discuss appropriate nutrition based on your individual needs and pregnancy health. After pregnancy and when breastfeeding is complete (if applicable), weight management tools and support become appropriate again.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.