How much weight gain is “normal”?

Pregnancy can lead to changes in many of your daily routines and habits, including what you eat and how much exercise you get. But most of all: Women’s bodies change during pregnancy to ensure that their unborn children get enough food and other things that they need. These changes already start happening in early pregnancy, and become more and more noticeable as time goes on. Women gain more weight in the final months of pregnancy than they do in the first few months. This isn't only due to the weight of the growing baby. Much of the weight gained is extra fluid (water) in the body. This is needed for things like the baby’s circulation, the placenta and the amniotic fluid.

Medical guidelines used to be quite strict, with recommendations limiting weight gain to a few kilograms. But there is no standard recommended amount of weight gain that applies to every pregnant woman. The recommendations are now based on women’s pre-pregnancy weight. Petite, underweight women should put on more weight than women who were overweight before they became pregnant.

The body mass index (BMI)

The body mass index (BMI) is the most common way to determine whether people are underweight, overweight or have a normal weight. It measures the relationship between weight and height. A BMI under 18.5 is considered to be underweight, a BMI between 18.5 and 25 is “normal weight,” and a BMI between 25 and 30 is “overweight.” If someone has a BMI over 30 they are considered to be very overweight (obese).

BMI alone is not enough to say whether someone’s weight is likely to cause health problems, though. So being overweight is absolutely fine for many people – unless they develop certain health conditions, such as type 2 diabetes. However, having a BMI above 30 (being obese) increases the risk of related health problems.

Body weight before and during pregnancy

The U.S. Institute of Medicine (IOM) issues guidelines that are followed by doctors around the world. Their recommendations about BMI and weight gain in pregnancy are as follows:

• For women who are underweight before pregnancy (BMI of less than 18.5): between 12.5 and 18 kilograms of weight gain during pregnancy.
• For women who are of normal weight before pregnancy (BMI of between 18.5 and 24.9): between 11.5 and 16 kilograms of weight gain during pregnancy.
• For women who are overweight before pregnancy (BMI of between 25 and 29.9): between 7 and 11.5 kilograms of weight gain during pregnancy.
• For women who are obese before pregnancy (BMI greater than 30): between 5 and 9 kilograms of weight gain during pregnancy.

A pregnant woman’s weight alone is not a good indicator of how well her baby is doing – and not even of how fast her baby is growing. That depends on a lot of factors. It is not possible to say for sure how much the baby will weigh at the end of pregnancy. Ultrasound scans and other tests can only give us a rough idea of how the baby is developing and how much he or she might weigh at birth.

Can putting on too much or too little weight be harmful?

Women who gain a lot of weight in pregnancy have a higher risk of certain health problems and complications during childbirth. For instance, they are more likely to have a very big child with a birth weight of over 4,000 g or 4,500 g (macrosomia), and are more likely to need a Cesarean section.

They are also more likely to have difficulties losing the extra weight after giving birth.

On the other hand, if a woman doesn't gain enough weight and doesn’t get enough different foods in pregnancy, it can harm her growing baby: babies are then often born too early (preterm birth) or often weigh too little at birth.

Very fast weight gain as a sign of health problems

If a woman puts on weight very suddenly, or if she generally gains more than half a kilogram per week, her weight will be monitored by a doctor or midwife. Additional tests and examinations might be needed too.

Very fast and extreme weight gain (such as 1 kilogram within a week) can be a sign of health problems such as pre-eclampsia. The main symptom of this pregnancy-related condition is high blood pressure, sometimes accompanied by nausea, headaches and dizziness too. Pre-eclampsia can be life-threatening for both the mother and her child, and it needs to be treated by a doctor as soon as possible.

Putting on a lot of weight in pregnancy can increase the risk of women developing diabetes in pregnancy (“gestational diabetes”) – or it can be a sign that they have developed it. Gestational diabetes is where blood sugar levels increase in women who didn't have diabetes before becoming pregnant. Gestational diabetes increases the risk of pre-eclampsia, and can result in the unborn baby putting on a lot of weight. Having a very big and heavy baby can delay the birth and make it more difficult for the woman to give birth to her child naturally (“spontaneously”).

Does avoiding too much weight gain have any advantages?

Paying special attention to diet and getting more exercise during pregnancy may lower certain health risks. This will depend on several factors, including whether the woman is overweight or has gestational diabetes. Research hasn't shown any advantages for women who have a normal weight.

But women who are very overweight (BMI of over 30) can lower their risk of gestational diabetes by changing their diet and getting more exercise. Previous studies haven't shown that this will lower the risk of complications during childbirth or prevent the need for a Cesarean section, though.

Women with gestational diabetes are advised to change their diet in order to lower their blood sugar levels. That can lower the risk of complications during childbirth.

Dietary changes and exercise during pregnancy

Because carbohydrates increase blood sugar levels, women who are very overweight or have gestational diabetes are usually advised to cut down on carbohydrates (“carbs”) while making sure that they still get enough fiber, and to generally eat a balanced diet otherwise. Other common advice includes eating three not-too-big main meals and two to three smaller meals per day.

The exact dietary changes to be made will depend on things like how much the woman weighs and how much exercise she gets. Getting special advice from a nutritional therapist can help to avoid adverse effects. Pregnant women need to make sure that they get enough calories and important nutrients, which is why they shouldn’t go on a low-calorie diet, for instance.

Doing at least 30 minutes of a strenuous physical activity on about three to four days per week is often enough. Suitable types of exercise include swimming, cycling and brisk walking. Women with a greater risk of preterm birth are usually advised to avoid sports altogether. When in doubt, don't hesitate to ask a gynecologist.

How can underweight pregnant women gain enough weight?

If a woman who is underweight becomes pregnant and finds it difficult to put on weight, she can seek advice from her doctor or midwife. Studies suggest that professional dietary advice can help women gain weight and lower the risk of giving birth too early (preterm birth).

Protein supplements have been found to help some underweight women increase their weight. This lowers the risk of their child being born underweight, as well as reducing the risk of having a miscarriage. However, very protein-rich dietary supplements with a protein content of more than 25% don't appear to help. Research also suggests that these very high-protein products might limit the growth of the baby. So it's important to make sure you get a balanced mix of nutrients. “More” is not “better” in this case.

Does watching your weight prevent stretch marks?

There is no clear answer to this question yet. Although there are many claims about what causes stretch marks and what might help, none of them have been confirmed in good-quality research.

Whether or not women get stretch marks not only depends on how much weight they gain in total. Factors like how fast they gain weight can make a difference too. For instance, gaining a lot of weight very suddenly can cause more stretch marks than gaining weight gradually. But it's not clear whether stretch marks can be prevented by keeping your weight down.

Losing weight after having a baby

Many mothers find that it takes a while before they reach their pre-pregnancy weight again. For some women, breastfeeding and taking care of a baby are enough to melt away the weight gained during pregnancy: It's as though they really need this stored up energy to help get through the first few weeks and months of motherhood.

But most women won't really get close to their pre-pregnancy weight until perhaps six months after giving birth. Women who don't lose weight, or even gain weight instead, might have a higher risk of health problems. These problems could get worse in other pregnancies.

The best way to lose weight is by combining a change in diet with extra physical exercise. Exercise alone probably won't do much. Programs to help people change their eating and lifestyle habits are often used to try to lose weight. In the research on these programs, women started weight control efforts a month or two after giving birth, and sometimes later. Immediately after birth, mothers need enough nutrients to breastfeed their child, so it is not a good time for them to try to lose weight.

Too much, or too sudden, weight loss can have disadvantages too. For instance, if you go on a diet that is too strict or too one-sided after having a baby, it could reduce the quantity of your breast milk or the nutrients it contains.

How do women feel about their weight in pregnancy and afterwards?

Women are constantly surrounded by (nearly always digitally edited) photos of models with supposedly “ideal” bodies. Pregnant women are confronted with these photos too. This makes it difficult for many of them to be happy with their figure, and it can damage their self-image and enjoyment of their body. The media add to the pressure on pregnant women and mothers by focusing a lot of attention on how quickly celebrities return to their pre-pregnancy figures. But women need to gain weight during pregnancy – and they can't expect to lose it all again within a few weeks after giving birth.

A lot of women see pregnancy as a time to simply enjoy their belly, curves and the baby growing inside their body – and allow themselves some “time off” from worrying about their size. That can be one of the really pleasant parts of being pregnant.

It could only become a problem if you get too far out of your normal weight range and change your eating habits too much. Then it might be harder to get back to your healthier “pre-baby” weight and lifestyle. Women who don't become very overweight when they are pregnant will probably find it easier to get back to normal afterwards. But you don't have to be thin to be happy and healthy, and have a healthy baby.

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