We've all heard the phrase 'eating for two' - but it's important to understand exactly how much weight gain in pregnancy is healthy, as eating too much or too little can be bad for your baby.
Many women find advice on weight gain during pregnancy confusing.
Although it's tempting to eat more when you're carrying your little one, being overweight and pregnant can put your baby at increased risk of complications like pre-eclampsia and gestational diabetes Obese women are also more likely to need a Caesarean.
How much weight should I gain in pregnancy?
Weight gain in pregnancy can vary hugely from woman to woman, but most pregnant women will gain between 22lbs to 26lbs whilst carrying their baby.
The majority of this weight gain will happen towards the end of the second trimester and into the third. 'Most of the weight will be the baby, placenta and amniotic fluid, but some will be fat to help with breastfeeding,' says Dr Matthew Prior, fertility consultant and medical director of Dr Fertility
As an expectant mum it's important to eat a healthy, balanced diet. Some mums-to-be suffer from pregnancy symptoms such as morning sickness and have no appetite in the first three months of pregnancy, but others say they're always hungry. You may feel better eating little and often, but make sure your diet is rich in vitamins and minerals.
How much weight should you gain each trimester?
How much weight you should gain each trimester very much depends on what you weigh at the beginning of your pregnancy. So to ensure you're gaining the right amount of weight, the best thing to do is speak to your GP or health care provider.
However, on average underweight women should gain 28 to 40 pounds and overweight women should gain 15 to 25 pounds, and 'most weight is added in the second half of pregnancy (after 20 weeks),' says Dr Prior.
How much weight should I have gained at 20 weeks?
20 weeks is approximately five months into your pregnancy. During the first three months, most women will gain between two to four pounds and one pound every month until the end of the pregnancy.
Naturally, if you are expecting twins, the about of weight you gain throughout your pregnancy will differ.
What should I do if I think I'm overweight during pregnancy?
'Losing weight is not a good idea during pregnancy as you need to get enough nutrition for yourself and the baby,' says Dr Prior. 'However, women who are overweight are advised to try and maintain their pre-pregnancy weight. Gaining too much weight during pregnancy puts you at risk of gestational (pregnancy) diabetes and high blood pressure.' According to Diabetes UK, approximately 16 out of every 100 women will develop gestational diabetes.
The old saying that you need to 'eat for two' just isn't true - you don't need to eat any extra calories until the last three months of your pregnancy - and even then, you only need around an extra 200 calories per day.
Keeping healthy during pregnancy will benefit you and your baby - and will help you to get back to healthy weight after birth. It is advised to eat healthily and do regular, gentle pregnancy exercises like swimming and brisk walking.
Talk to your doctor or midwife if you're concerned you're overweight and pregnant, as they'll be able to give you advice.
Can you gain too little weight during pregnancy?
If you don't gain enough weight during pregnancy this could result in some issues for your baby such as being born prematurely or having a low birth weight.
If your baby weighs less that 5.5lbs at birth this is classed as being underweight, so it's important get as many nutrients into your body as possible to try and avoid this happening.
Some women are naturally slim and will stay a similar size whilst they are pregnant which is fine, but if you are eight stone or under your doctor may have some special advice for you.
What causes rapid weight gain in early pregnancy?
Rapid weight gain (such as 1kg a week) in early pregnancy is definitely something to be aware of, as it can be indicative of other serious health problems. According to the National Center for Biotechnology Information (NCBI) in the US, one of the reasons for rapid weight gain in pregnancy early on could be due to pre-ecalampsia. The charity, Tommy's, highlights that pre-eclampsia affects up to 6% of pregnancies in the UK. Severe pre-eclampsia develops in around 1-2% of UK pregnancies and 1 in 6 women who have had pre-eclampsia will have it again in a future pregnancy. This is characterised by high blood pressure, dizziness, nausea and headaches, it can be life-threatening to both baby and mother in some cases, so it's important that it's treated as soon as possible.
Overeating is another common cause. 'Your body is pretty amazing, in that it absorbs nutrition more efficiently during pregnancy and gets more out of what you eat compared with a non-pregnant woman,' says Dr Prior. 'So, if you eat an extra 450 calories a day in early pregnancy, the amount required in the third trimester, you will put on an extra pound a week from overeating.'
However, there are also plenty of other reasons why you might be experiencing rapid weight gain. The best way to make sure that you and your baby are in perfect health is to visit your health care provider or GP.
Pregnancy weight gain timeline and breakdown
Judging how well a baby is doing, and how fast it's growing, by a pregnant woman's weight is generally not a good idea according to the NCBI. As it depends on many factors, it's not always possible to say how much the baby will develop and how much weight a pregnant woman will gain by the end of the pregnancy.
It's only through ultrasound scans and other tests that an idea of baby development is given.
The US Institute of Medicine (IOM) has guidelines surrounding weight gain in pregnancy that's followed around the world. They break down pregnancy weight gain using Body Mass Index (BMI) and the following timeline...
- Underweight women (BMI of less than 18.5): between 12.5 and 18 kg of weight gain during pregnancy.
- Women of an average weight (BMI of between 18.5 and 24.9): between 11.5 and 16kg of weight gain during pregnancy.
- Overweight women (BMI of between 25 and 29.9): between 7 and 11.5kg of weight gain throughout pregnancy.
- Obese women (BMI of more than 30): between 5 and 9kg of weight gain throughout pregnancy.
This is by no means an exhaustive and entirely inclusive breakdown of a pregnancy weight timeline. For a breakdown of how much weight you should gain through your own pregnancy, it's best to visit your GP.
Pregnancy weight gain: Is my bump too big?
Women often compare their bumps with each other and then worry that theirs is 'too big' or 'too small'. The size is dictated by many things, not just how big or small your baby is.
Some people think your bump size can depend on whether you're having a boy or girl, which for curious mums can be guessed at just 12 weeks with the nub theory. It may be the position in which your baby is lying, how tall you are, how many babies you've had before and, obviously, how many you're carrying!
But how will I know if my bump is the right size?
At each ante-natal appointment, your midwife will feel your abdomen and measure the distance from the top of the uterus to your pubic bone. Each week of pregnancy will measure about 1cm (1/2 in) on your bump.
If she feels that your baby isn't growing as well as he should be, she may send you for a scan to measure the growth or for a consultant opinion. If your baby feels significantly larger than expected, she'll do a blood test to rule out diabetes (glucose load test). But remember, not all babies are average size, and there will always be some that are bigger and some that are smaller.
What if my baby is too large?
Few babies are too big to push out. Babies tend to grow to 'fit' their mum's pelvis, but if they're genuinely too big to come out vaginally, your midwife will pick up on signs during labour. Sometimes babies have a 'deflexed head' during labour. This is when their chin isn't tucked onto their chest but is looking slightly up, which increases the dimension that has to go through the pelvis.
With good, strong contractions, however, the position can change. If your baby is 'too big' - a condition called cephalopelvic disproportion (CPD) - you'll need a C-section. According to the NHS, around 1 in 4 pregnant women in the UK has a caesarean birth.
'Professionals are more interested in identifying babies that are too small,' says Dr Prior. 'Small babies may be a sign that they are not growing properly and more likely to run into problems. Measuring babies is difficult, so your midwife may arrange a scan if your bump is too small.'
What can affect the growth of my baby?
The source of nutrition and oxygen for your baby is the placenta, so if this isn't working as efficiently as it should be, it can slow down the growth. High blood pressure or pre-eclampsia can affect the placenta, as can smoking and malnutrition.
Diabetes in the mum-to-be can also affect a baby's growth, either slowing it down or, more commonly, causing it to become large before term. But diabetic mums will have close antenatal care and regular scans monitoring their baby's growth, development and wellbeing.
'Big babies are linked with having a big baby in previous pregnancies, or with diabetes in the mother,' says Dr Prior. 'Small babies can be due to placental problems, smoking in pregnancy, or unexplained causes.' If you're not sure, always speak to your midwife or doctor.
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Rose Goodman joined Future Publishing in 2020 and writes across Goodto.com, Woman & Home, Woman, Chat and Woman’s Own magazines. Prior to pursuing her career as a writer, Rose obtained a degree in psychology and went on to work in adult mental health for five years at Addenbrooke’s Hospital, Cambridge, specialising in eating disorders. She is fully trained in first aid, medical emergency response and motivational interviewing – a directive, patient-style counselling approach to address ambivalence in recovery. She graduated with a MA in creative writing from the University of Brighton in 2017. In her spare time she enjoys writing poetry and attending literary events, and offers weekly support to those living with homelessness. Rose has a passion for raising awareness around mental illness and the importance of prioritising our wellbeing.
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