During pregnancy, your body will grow and change — as you probably well know, if you’re expecting. These changes will become even more fast and furious as you get closer to your delivery date.

For some, these changes can be a little disconcerting. But if you’re worried you’re gaining too much weight, it’s important to know that there’s a wide range of what’s considered healthy.

If you’re still concerned, you may wonder if intermittent fasting (IF) can help you manage your weight and other health concerns during pregnancy. Or maybe you’ve already been practicing intermittent fasting and want to know if you can continue for the next 9 months.

What should you do? Well, before you make any changes to your eating habits, it’s a good idea to call your doctor to go over the pros and cons. In the meantime, here’s the 411 when it comes to IF and pregnancy.

What you need to know

Intermittent fasting is not recommended during pregnancy.

Related: Weight before pregnancy is a bigger health factor than weight gain during pregnancy

People who engage in intermittent fasting eat the bulk of their calories within a certain period of time. There are several approaches to this way of eating.

For example:

  • Some people eat daily, choosing a specific window in which to eat. In the 16:8 method, you might choose to eat between the hours 12 p.m. and 8 p.m. each day — meaning you’re eating in an 8-hour window. The other 16 hours out of the day are considered fasting.
  • Alternatively, people may choose to eat normally some days of the week, say 5 days, and fast (or eat a couple low-calorie meals) on the other 2, like in the5:2 method.

There’s a good amount of research surrounding intermittent fasting and how it puts the body into a fat-burning state called ketosis. Beyond that, fasting regularly may help:

And other research suggests that fasting may lower risk factors for things like diabetes, cardiovascular disease, and some cancers.

Weight loss is a big focus of research on IF, and fasting is believed to help with shedding weight because it shifts the body to running on fat stores. It may also help reduce overall caloric intake.

In one small 2007 study, participants lost a whopping 8 percent of their body weight in just 8 weeks following alternate day fasting. This means they ate normally every other day and consumed just 20 percent of their normal calories on the “off” days.

Related: 10 health benefits of intermittent fasting

Always speak to your doctor before making any significant changes to your diet and exercise habits.

Intermittent fasting is generally not recommended to women during pregnancy.

There isn’t a whole lot of research to provide informed recommendations on whether there are positive or negative effects on the pregnancy. There are no studies that looked at intermittent fasting over the entire pregnancy.

Many of the studies you’ll find on pregnant women and fasting revolve around the Muslim holiday of Ramadan, which is about 30 days. During this lunar month, people fast from sun up to sun down. While pregnant and breastfeeding women are technically exempt from the practice, some still carry on with fasting.

  • An older 1996 report noted a study on Gambian women suggests that those who fasted during Ramadan did experience big changes in their glucose, insulin, and triglyceride levels, as well as in other health markers. The weight of their babies at birth, however, was comparable to the babies of women who didn’t fast. Still, the researchers explain that fasting during pregnancy may have health implications that appear later in life and should, therefore, be avoided.
  • A more recent study echoes these results and showed that fasting for Ramadan didn’t impact birth weights of babies. Beyond that, there was no association with fasting and preterm delivery. Just as in the previous study, though, the researchers conclude that more study is needed on fasting and its potential adverse health effects.

One thing we know is that pregnancy is a time when you need to focus on:

  • helping your baby gain weight
  • providing nutrition to help with brain and body development
  • developing maternal fat stores if you plan to breastfeed

Dramatically changing eating habits may lead to nutritional deficiencies and other health issues for both you and baby. Fasting may also alter hormone levels.

Notably, studies that look at IF and pregnancy deal primarily with birth weight. There are so many other possible outcomes that haven’t been studied — such as risk of pregnancy loss and later effects on children whose mothers did IF, for example.

Above all, the way fasting affects your body and pregnancy is unpredictable and likely different from how it may affect somebody else. For this reason, the American College of Obstetricians and Gynecologists recommends that you work with your healthcare provider to develop an individual plan for weight gain based on your body mass index (BMI) and overall health.

For women with BMIs in the 18.5 to 24.9 range, this typically means gaining between 25 and 35 pounds eating a balanced diet of whole foods and drinking plenty of water. Those with more weight may need to control gain under the guidance of a doctor with careful monitoring of their baby’s growth.

What if I practiced IF before pregnancy?

We may sound like a bit of a broken record, but speak with your doctor — even if you’re already in a fasting groove that works for you. It may be OK for you to continue fasting, just not quite as intensely as you might be used to.

Be sure to tell your doctor your entire history with intermittent fasting, as well as your goals with continuing it during pregnancy.

Related: The third trimester: Weight gain and other changes

While the long-term implications aren’t totally clear, researchers did examine women fasting for Ramadan and how it affected things like fetal breathing. When women had low glucose levels from fasting, it took them a “significantly” longer amount of time to detect fetal movements.

Low frequency of fetal movements is generally considered a warning sign you need to take seriously, especially as you get closer to your delivery date. Your baby should make around 10 movements within 1 to 2 hours — and you should usually be able to feel 10 movements within just half an hour.

With restricting eating to certain windows or days, it may also be difficult to get the right amount of nutrition in when you are eating. This is made even more difficult because your baby is pulling from your nutrition stores as well.

Issues like iron deficiency anemia are already more common in pregnant women. And when a baby doesn’t get enough iron — particularly in the third trimester — they may be at higher risk of developing anemia before their first birthday. This is scary stuff, but fortunately, getting good nutrition makes these risks go way down.

Related: Health risks associated with pregnancy

To keep weight gain steady but healthy, most women should aim to consume 300 extra calories each day. That’s a little extra — like a glass of skim milk and half a sandwich — but certainly not the “eating for two” you may have heard before you got pregnant.

Exercise is another part of the equation. You may feel cruddy — especially in the first trimester — but moving your body may even lower your risk of gestational diabetes, help shorten your labor, and reduce your cesarean delivery risk.

If you’ve exercised before pregnancy — great! Ask your doctor if you need to modify your routine and keep going. If you’re new to workouts, focus on getting around 30 minutes each day of moderate activity, like walking, swimming, or cycling on a stationary bike.

Related: Maintaining a healthy pregnancy

Now, for some pretty cool news. Studies show there’s a “mutually beneficial” link between diet and fertility.

Intermittent fasting may have some power when it comes to fertility in women with polycystic ovary syndrome (PCOS). In one recent study, women with obesity and PCOS who fasted regularly saw an increase in their levels of luteinizing hormone, which is responsible for aiding in ovulation.

Other information suggests that weight loss of 5 to 10 percent may help with reproduction. Since intermittent fasting may help in this area, as well as with insulin resistance and other health issues, it’s possible that fasting may “enhance” overall fertility and health of the reproductive system.

Related: A look at your fertility timeline

It’s probably not a good idea to delve into fasting during pregnancy — especially if you’ve never tried it before.

The good news is that pregnancy doesn’t last forever, and you can definitely try this method of eating to lose weight after you deliver. (But again, check with your doctor — who just might be your BFF by now — if you’re breastfeeding.)

And if you’re feeling overwhelmed, do ask for help. Your healthcare provider will track your weight at each of your prenatal appointments. Talk about your concerns about gaining too much to see if they have suggestions to help you scale back — if needed — in a way that keeps both you and baby healthy and on target.