Blood Sugar Before, During, and After Pregnancy

Blood sugar doesn't suddenly become relevant when someone is diagnosed with gestational diabetes. Changes in insulin sensitivity can matter before conception, throughout pregnancy, and after delivery, and understanding those changes can make some of the confusing advice around women's metabolic health easier to put into context.

We recently brought Lily Nichols, RDN, together with Celeste Hughes for a live conversation about exactly that. Lily is the author of Real Food for Pregnancy and Real Food for Fertility, and Celeste joined the conversation while 38 weeks pregnant with her third child. They talked about insulin resistance and fertility, the metabolic changes that happen during pregnancy, what contributes to gestational diabetes, and what a gestational diabetes diagnosis can mean after pregnancy.

They also got into the practical questions people actually ask: Does eating sugar cause gestational diabetes? Does breakfast matter? What about caffeine during pregnancy? And where does intermittent fasting fit when someone is trying to conceive? Here are some of the key takeaways from their conversation.

Why blood sugar matters—even if you don't have diabetes

When we think about blood sugar, diabetes is usually the first thing that comes to mind. But blood sugar regulation is something the body is working on all day, every day. Lily explained that insulin resistance can develop before blood glucose reaches the range associated with prediabetes or diabetes. The pancreas can compensate by producing more insulin, which means a glucose test may still look normal even while insulin levels are elevated.

For women, that connection can extend to reproductive health. Insulin and glucose signaling interact with ovarian function, and Lily discussed research connecting higher glucose levels—even below the diagnostic threshold for prediabetes—with longer time to conception. She also explained that elevated insulin before pregnancy can affect ovarian testosterone and other hormones involved in ovulation.

At the same time, lower isn't always better. Significant undereating and low energy availability can also interfere with ovulation. Lily described a “sweet spot” between being undernourished and eating in a way that contributes to consistently high insulin levels and insulin resistance. Supporting fertility isn't about eating as little as possible or chasing the lowest possible blood sugar reading; adequate nutrition and metabolic health both matter.

What happens to insulin resistance during pregnancy?

Pregnancy creates a unique metabolic environment. Lily explained that insulin sensitivity can improve during the earliest stages of pregnancy, when women may be more prone to lower blood sugar. As pregnancy progresses, placental hormones, changes in the pancreas, normal weight gain, and other physiological changes gradually make the body more insulin resistant.

Some degree of insulin resistance during pregnancy is normal and helps keep energy and glucose available for the growing baby. The pancreas responds by producing additional insulin to keep blood glucose within an appropriate range. Gestational diabetes can develop when the body can't produce enough insulin to compensate for that increased insulin resistance.

Later in the conversation, Lily described pregnancy as a kind of metabolic “stress test.” The increased metabolic demands of pregnancy can bring glucose-regulation problems to the surface that may not have been obvious beforehand.

Does eating sugar cause gestational diabetes?

This was one of the questions submitted for the conversation, and Lily's answer was more nuanced than a simple yes or no. What someone eats can influence risk, but gestational diabetes isn't simply the result of eating too much sugar.

During pregnancy, placental hormones naturally increase insulin resistance. If the pancreas can produce enough additional insulin, blood glucose can remain appropriately regulated. If it can't compensate, glucose can begin to rise.

Lily also emphasized that gestational diabetes doesn't look metabolically identical in every woman. She discussed different presentations involving insulin resistance, insufficient insulin production, or some combination of the two. In the research she described, insulin resistance accounted for the majority of cases, but not all of them.

Other factors can influence risk as well. Lily discussed PCOS, family history of diabetes, body composition, pregnancy weight gain, and previous pregnancy history. Some of those factors can be influenced, while others can't. A gestational diabetes diagnosis, then, isn't a simple judgment about whether someone ate the “right” foods during pregnancy.

What can women do to support healthy blood sugar?

When Celeste asked what women could realistically do to support insulin sensitivity—especially while managing children, work, and busy schedules—Lily started with something practical: breakfast.

She discussed research in which people eating a protein-rich breakfast tended to have better blood sugar and insulin patterns throughout the day, along with better energy and lower self-reported hunger. Her suggestions weren't complicated: eggs, Greek yogurt, nuts, egg bites, or another convenient source of protein that works with your morning routine.

Movement after meals was another recommendation. That doesn't necessarily mean scheduling a workout every time you eat. Lily suggested that even a 10-minute walk, a handful of squats, or calf raises can get muscles working after a meal and help reduce glucose.

Meal timing came up, too. Lily explained that eating a large amount of food immediately before a long period of rest isn't ideal from an insulin-sensitivity perspective, but she added an important qualification: avoiding a large late meal is much more realistic when you've eaten enough earlier in the day. If you're barely eating during the day and arrive at night extremely hungry, the problem isn't simply that dinner was too late.

Taken together, her advice was practical rather than extreme: get enough protein earlier in the day, move after meals when you can, and pay attention to when you're eating.

How quickly can better habits make a difference?

Changes in hunger and energy can sometimes be noticeable quickly. Lily said someone might feel a difference as early as the next meal after changing what they eat. Hormonal and menstrual-cycle changes generally take longer and depend heavily on the individual and how disrupted things were to begin with. In some cases, she has seen changes during the next menstrual cycle or over the following few cycles.

Rather than trying to overhaul everything at once, Lily recommended experimenting with a manageable change for a few days and seeing how you feel. If it helps and fits your life, keep doing it until it becomes normal. Her point was less about finding a new health “hack” and more about building something you can do consistently.

What does gestational diabetes mean after pregnancy?

A gestational diabetes diagnosis is tied to pregnancy, but the information it provides can remain relevant afterward. Lily explained that having gestational diabetes is associated with a higher risk of developing type 2 diabetes later in life, although that risk varies considerably from person to person.

During the conversation, she cited research estimating a 30–70% progression to type 2 diabetes among women who have had gestational diabetes. She also emphasized that increased risk isn't a guarantee. The underlying metabolic characteristics and severity of gestational diabetes can differ, and diet and lifestyle after pregnancy can influence long-term metabolic health.

The postpartum period brings its own nutritional and metabolic demands. Lily discussed breastfeeding, when possible and desired, and the substantial amount of energy required to produce breast milk. She also placed particular emphasis on getting enough protein after pregnancy, especially during breastfeeding.

Exercise can gradually become part of the picture as recovery progresses. Lily emphasized giving the body time to heal before jumping back into an exercise routine. Once recovered, she recommended incorporating resistance training and rebuilding muscle, which plays an important role in glucose use.

What about caffeine during pregnancy?

Caffeine was another audience question, and Lily's answer focused on total intake rather than any one beverage. She referenced the general recommendation of keeping caffeine intake below about 200 milligrams per day during pregnancy, counting caffeine from all sources. She noted that an 8-ounce cup of coffee contains roughly 100 mg, although the actual amount varies with preparation and serving size.

Coffee isn't the only source of caffeine. Black tea, green tea, white tea, and yerba mate all contain it, and consuming several different caffeinated drinks during the day can add up. Lily also noted that individual responses vary: some people metabolize caffeine quickly, while others are much more sensitive to its effects.

For pregnancy, the useful number to pay attention to is your total caffeine intake from all sources, rather than simply how many cups of coffee or tea you drink.

Intermittent fasting and fertility: Is it a good idea?

Before asking about intermittent fasting, Celeste made an important distinction: the question was about women trying to conceive, not fasting during pregnancy.

Lily explained that research specifically examining intermittent fasting in women remains limited. She discussed studies involving women with PCOS who were overweight and insulin resistant in which a shorter eating window produced favorable outcomes, but the way those studies were designed matters.

In the research Lily described, the women weren't simply skipping breakfast and dramatically reducing calories. They ate enough food within a shorter eating window that occurred earlier in the day. One protocol used an eating window from approximately 8 a.m. to 4 p.m. while maintaining caloric intake.

That situation is very different from someone who is already undereating, highly active, or experiencing irregular or missing menstrual cycles. Lily said she doesn't recommend intermittent fasting in those circumstances because further restriction may add physiological stress.

She also discussed another study in women with PCOS that didn't use intermittent fasting. One group ate a larger breakfast, moderate lunch, and smaller dinner, while another followed the opposite pattern. According to Lily, the larger-breakfast group experienced many of the same benefits seen in the time-restricted eating research.

The more useful question, then, isn't simply whether intermittent fasting is good or bad. It's whether a particular eating pattern makes sense for the individual, including whether she's eating enough, her metabolic health, activity level, menstrual-cycle regularity, and fertility goals.

Start with something you can keep doing

One idea resurfaced throughout Lily and Celeste's conversation: supporting metabolic health doesn't have to begin with an overhaul. A protein-rich breakfast can be a starting point. So can walking after a meal, eating enough earlier in the day, or gradually building and maintaining muscle when it's appropriate.

Blood sugar, fertility, pregnancy, and gestational diabetes are complex subjects, and individual circumstances matter. What stood out from the conversation was how often Lily returned to matching the approach to the person rather than applying one rule to everyone.

For someone trying to conceive, that might mean looking at whether she's eating enough before experimenting with a fasting window. During pregnancy, it means recognizing that changes in insulin sensitivity are part of normal physiology while still paying attention to metabolic health. After gestational diabetes, it means recognizing increased future risk without treating that future as predetermined.

You don't have to change everything at once. Find one change that feels doable, give yourself time to see how it works for you, and build from there.

This blog post is for educational purposes only and is not intended to diagnose, treat, cure, or prevent any disease or replace individualized medical advice. If you are pregnant, trying to conceive, have gestational diabetes, or have questions about your blood sugar, talk with a qualified healthcare professional.