Pregnancy and Weight Gain

If you are trying for a baby, experts agree that being a healthy weight makes it easier for most women to conceive and fall pregnant. Dietitian, Juliette Kellow reveals all...

Your Weight Before Pregnancy

By Dietitian, Juliette Kellow BSc RD

It’s well established that being underweight or overweight can reduce fertility, making it harder for some women to get pregnant. In particular, women who are overweight or obese are at greater risk of suffering from insulin resistance.

This condition is a precursor for type 2 diabetes and means the body is less sensitive to the affects of insulin so that more of this hormone needs to be pumped out to lower blood sugar levels. But insulin resistance can also make it harder to get pregnant because can affect ovulation and can cause irregular menstrual cycles.

Insulin resistance doesn’t just affect the chances of conceiving either. During pregnancy, it also increases the risk of gestational diabetes. All women become slightly more insulin resistant when they are pregnant because the placenta creates anti-insulin hormones that make it harder for insulin to do its normal job of lowering blood sugar levels.

For women who are already insulin resistant when they fall pregnant, blood sugar levels can rise even more during pregnancy, resulting in diabetes. Unfortunately, the excess sugar in the blood can directly affect the size of the developing baby. If the baby gets too much ‘nourishment’ via the placenta, it can grow really big, making it harder to deliver.

Babies are also more likely to suffer with jaundice and be at higher risk themselves for developing obesity and type 2 diabetes in later life. Mums-to-be with gestational diabetes can also have problems. For example, they are more likely to suffer with urinary tract infections and may need a caesarean section. They also have an increased chance of developing diabetes in later life or in a subsequent pregnancy.

Being obese also puts women at risk of high blood pressure. During pregnancy, this can lead to a condition called pre-eclampsia, which increases the risk of stroke, may impair kidney and liver function, can cause blood clotting problems, pulmonary oedema (fluid on the lungs) and seizures, and, in severe forms, death of the mother and/or baby. Plus, because pre-eclampsia affects the flow of blood to the placenta, babies can be smaller and are often born prematurely.

Sadly, research also shows that being obese is linked to a higher rate of miscarriage and can increase the risk of congenital malformations, particularly to the heart and spine of a developing baby.

In the largest study of its kind, scientists from the University of Texas recently found that seven different types of birth defect were more common in babies whose mothers were obese. The research, published in the Archives of Pediatrics and Adolescent Medicine, revealed these to be spina bifida, heart defects, genital and bowel abnormalities and small or missing toes, fingers, arms and legs.

According to Dr Daghni Rajasingam, Consultant Obstetrician and spokesperson for the Royal College of Obstetricians and Gynaecologists, being obese doubles your risk of having a baby with a birth defect. Amongst women of a healthy weight, three babies in 100 will have a serious birth defect – in obese women, this rises to six babies in 100.

When it comes to giving birth, being obese can even make delivering the baby much harder and caesarean sections are more commonly needed.

Then, once the baby has been born, women who were overweight before they became pregnant often find it even harder to shift those pounds after giving birth.

Top Tips - Your Weight Before Pregnancy

  • Before you even start trying for a baby, aim to get to a healthy body weight – or as near to it as possible. If you’re very overweight, aiming for a BMI of 25 or below might not be realistic. However, any weight you lose could help you to conceive and have a healthy pregnancy.
  • Even though you might need to lose weight, now’s not the time to start faddy or crash diets. Any diet that severely restricts your food intake or avoids groups of foods will leave you short on a range of important vitamins and minerals. Instead, aim to eat a healthy, balanced diet with a moderate calorie restriction to shift those pounds. This will help to ensure your body’s nutrient stores remain topped up so that when you do conceive, your body will be able to cope with the demands of pregnancy.
  • Start being more active – as well as helping you to lose weight, exercising regularly will improve your fitness levels, strength and stamina. This will benefit you throughout your pregnancy and may help to make the birth easier.
  • Before you start trying for a baby, make an appointment to see your GP or practice nurse. Being overweight or obese increases the risk of health problems such as insulin resistance, type 2 diabetes and high blood pressure. Often these conditions have no symptoms so you may not know you have them unless you are tested. All these conditions can cause problems during pregnancy so it’s important to get checked for them before you conceive. The good news is, even if you are diagnosed with a health problem, there’s good treatment available and it shouldn’t hinder your chances of having a healthy pregnancy.
  • Take folic acid supplements each day. The Department of Health recommends all women who are planning a pregnancy take a 400 microgram supplement of folic acid each day. This B vitamin is essential for the healthy development of a baby’s brain and spinal cord and so helps to reduce the chances of having a baby with spina bifida. However, if you are obese or suffer with diabetes, you should take a 5 miligram supplement of folic acid. This is because both of these conditions increase the risk of congenital abnormalities. Supplements of 5mg folic acid are only available on prescription so you’ll need to see your GP.
  • Consider taking a supplement that’s specifically designed for pregnancy such as Vitabiotics Pregnacare or Sanatogen Pronatal (both of which include folic acid). Taking a supplement will help to build up your nutrient stores. But don’t think supplements are a substitute for a healthy diet – they aren’t!
  • Avoid taking supplements that contain vitamin A, including cod liver oil capsules, as this vitamin is stored in the body and experts believe that too much may harm a developing baby. It’s also important to avoid liver and liver products such as pâté as they are rich sources of vitamin A.
  • If you’re a fan of fish, you might need to eat less or avoid certain varieties. The Food Standards Agency (FSA) recommends avoiding shark, swordfish or marlin and having no more than four cans of tuna or two fresh tuna steaks a week as these can contain high levels of mercury, a heavy metal that can harm the nervous system of a developing baby.
  • New advice from the Department of Health recommends avoiding all alcohol when you’re trying to conceive and throughout pregnancy. If you can’t give it up altogether, have no more than one to two units of alcohol once or twice a week to reduce the risk of having a baby with Foetal Alcohol Syndrome. Also, remember booze contains calories but little else so drinking lots won’t help you to shift those pounds.

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More Information

Visit the Food Standards Agency website at for advice on healthy eating and information about diet before and during pregnancy.

Visit the British Nutrition Foundation at

Your midwife should be able to give you advice on healthy eating during pregnancy, suitable weight gain and breastfeeding.

The Pregnancy Book 2007 by the Department of Health is available on line at

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