A baby’s growth percentile during pregnancy reflects how their estimated size compares to other babies at the same gestational age. If your provider has flagged a lower percentile, there are real, evidence-backed steps you can take to support fetal growth. Most involve optimizing your nutrition, blood flow to the placenta, and overall health. That said, it’s also worth knowing that ultrasound weight estimates carry a margin of error, so a single reading doesn’t always tell the full story.
What Growth Percentiles Actually Mean
When your provider says your baby is in the 30th percentile, it means your baby’s estimated weight is higher than 30% of babies at the same gestational age. This is not a grade. Babies in the 20th or 30th percentile are often perfectly healthy and simply smaller. The clinical concern starts when estimated weight drops below the 10th percentile, which is the threshold for fetal growth restriction (also called intrauterine growth restriction or IUGR).
Growth restriction below the 10th percentile can sometimes signal that the placenta isn’t delivering enough nutrients or oxygen. But even this diagnosis requires context. Genetics play a large role in baby size. If both parents are smaller, a baby in a lower percentile may be growing exactly as expected. What matters most is whether the baby’s growth is following a consistent curve over time or suddenly dropping off.
Ultrasound Estimates Have a Margin of Error
Before making changes based on a single growth scan, it helps to know how accurate these measurements really are. Ultrasound weight estimates are generally considered acceptable if they fall within 10% of the baby’s actual weight, and in recent years, accuracy has improved to consistently produce errors below 10%. However, the margin of error tends to increase in late pregnancy, when getting precise measurements becomes more difficult. A baby estimated at the 25th percentile could realistically be at the 15th or 35th. If one scan shows a lower-than-expected percentile, your provider will typically schedule follow-up scans to track the trend rather than relying on a single number.
Nutrition That Supports Fetal Growth
What you eat is the most direct lever you have over your baby’s growth. The goal is balanced energy and protein intake, not simply eating more of everything. The World Health Organization has found that balanced protein and energy supplementation during pregnancy promotes healthy gestational weight gain and reduces the risk of having a small-for-gestational-age baby. The key word is “balanced.” Protein should make up less than 25% of your total calorie intake. High-protein supplementation on its own does not appear beneficial and may actually be harmful to the fetus.
In practical terms, this means focusing on nutrient-dense meals that include a mix of protein sources (eggs, lean meat, fish, beans, dairy), complex carbohydrates, healthy fats, and plenty of fruits and vegetables. If you’re underweight or not gaining enough during pregnancy, increasing your overall calorie intake is important. Your provider can help you identify a target weight gain range based on your pre-pregnancy weight. For most people, the second and third trimesters require roughly 300 to 450 extra calories per day, which is less dramatic than it sounds: a yogurt with granola and fruit, or a handful of nuts with cheese.
Iron and folate deficiencies can also affect fetal growth, so continuing your prenatal vitamin and addressing any diagnosed deficiencies matters. If blood work shows you’re anemic, treating that anemia can improve oxygen delivery through the placenta.
Improve Blood Flow to the Placenta
Your baby’s growth depends entirely on how well the placenta delivers nutrients and oxygen. Anything that improves blood flow through the uterine and umbilical arteries can, in theory, support better growth. Several strategies have measurable effects.
Stay Physically Active
Gentle, regular movement improves circulation throughout your body, including to the uterus. A randomized controlled trial on yoga during high-risk pregnancy found that women who practiced guided yoga and visualization had significantly better blood flow through the umbilical artery, uterine artery, and fetal middle cerebral artery compared to women who didn’t. These improvements showed up as early as 20 weeks of gestation and persisted at 28 weeks. You don’t need to do yoga specifically. Walking, swimming, and prenatal exercise classes all promote healthy circulation. The goal is consistent, moderate activity rather than intense workouts.
Sleep on Your Left Side
Sleep position matters more than most people realize, especially in the second half of pregnancy. When you sleep on your back, the weight of your uterus compresses a major blood vessel (the inferior vena cava), which reduces blood flow to the placenta. Studies have shown that supine sleeping reduces cardiac output compared to left-side sleeping, and prolonged back sleeping is independently associated with lower birth weight and even stillbirth. Research suggests that about 80% of pregnant women spend some time sleeping on their back, with the average being about a quarter of the night.
Switching to your left side maximizes blood flow to the uterus. A body pillow behind your back can help you stay in position. If you wake up on your back, don’t panic. Simply roll to your side and go back to sleep.
Manage Blood Pressure and Preeclampsia Risk
High blood pressure narrows blood vessels, including those feeding the placenta. Conditions like preeclampsia and chronic hypertension are among the most common causes of fetal growth restriction. If you have risk factors for preeclampsia (previous preeclampsia, chronic hypertension, diabetes, kidney disease, or carrying multiples), your provider may recommend low-dose aspirin starting between 12 and 16 weeks of pregnancy. Studies have shown that when started before 16 weeks, low-dose aspirin reduces the risk of fetal growth restriction by roughly 44%. This is specifically for women at high risk of preeclampsia, not a blanket recommendation for all pregnancies.
Reduce Stress Where You Can
Chronic stress during pregnancy raises cortisol levels, and sustained high cortisol can cross the placental barrier and affect fetal development. The placenta has a built-in protective enzyme that converts cortisol to an inactive form before it reaches the baby. But when stress is chronic and cortisol stays elevated, this barrier gets overwhelmed. Research consistently shows that pregnant women with higher stress levels generally have smaller babies, with cortisol exposure linked to both lower birth weight and preterm labor.
You can’t eliminate all stress from your life, but targeted relaxation practices appear to help. The same yoga study that showed improved placental blood flow specifically used visualization and guided relaxation techniques. Even 15 to 20 minutes of intentional rest, deep breathing, or meditation each day can lower circulating stress hormones. Prioritizing sleep, asking for help with responsibilities, and reducing your workload where possible all contribute.
What to Avoid
Some factors that restrict fetal growth are within your control. Smoking is one of the strongest preventable causes of growth restriction, as it constricts blood vessels feeding the placenta. Quitting at any point during pregnancy improves outcomes. Alcohol and recreational drugs also impair fetal growth directly. Even high caffeine intake (above 200 mg per day, roughly two small cups of coffee) has been associated with lower birth weight in some studies.
Interestingly, bed rest is not helpful. The Society for Maternal-Fetal Medicine specifically recommends against activity restriction as a treatment for fetal growth restriction. Staying immobile actually reduces circulation, which is the opposite of what a growing baby needs.
When Growth Restriction Is Diagnosed
If your baby’s estimated weight falls below the 10th percentile, your provider will increase monitoring to track the baby’s well-being. This typically involves more frequent ultrasounds to measure growth trends, along with tests that check blood flow through the umbilical cord and assess the baby’s movement, breathing, and amniotic fluid levels. Up to 20% of early-onset growth restriction (before 32 weeks) is associated with genetic or chromosomal factors rather than placental issues, so additional testing may be offered depending on when the restriction is detected and whether other findings are present.
In cases where growth restriction is caused by poor placental function, no medication has been proven to reverse it once it’s established. The focus shifts to monitoring the baby closely and timing delivery to balance the risks of prematurity against the risks of staying in an environment where the placenta isn’t keeping up. For mild growth restriction near term, this often means delivery around 37 to 39 weeks. For more severe cases earlier in pregnancy, the timing depends on how the baby is tolerating the situation based on blood flow studies and other surveillance.
The most effective strategies are preventive: optimizing nutrition, staying active, managing blood pressure, reducing stress, and avoiding harmful substances. These won’t guarantee a jump from the 20th to the 60th percentile, because genetics set a range for your baby’s size. But they give your baby the best chance of reaching their full growth potential with the healthiest possible placental support.