Pregnancy Weight Gain by Trimester: Reference Rates

Pregnancy weight-gain guidance uses prepregnancy BMI, the number of babies and clinical assessment. A chart describes reference ranges; it cannot establish from your weight alone whether your pregnancy is progressing well. CDC recommends discussing goals with your pregnancy-care professional.

This guide explains the original U.S. Institute of Medicine/National Research Council recommendations, published in 2009, which CDC still references. It does not prescribe a diet or promise a predictable week-by-week pattern.

Trimester-by-Trimester Breakdown

The original guideline's Table 7-3 provides the following singleton pregnancy references. Its second- and third-trimester rate calculations assume 0.5–2 kg (1.1–4.4 lb) gain in the first trimester. That assumption is not proof that every gain outside it is abnormal or that weight loss is harmless.

Prepregnancy BMI category	Total gain, kg (published lb range)	Second and third trimester, kg/week: mean (range)
Underweight, BMI below 18.5	12.5–18 (28–40 lb)	0.51 (0.44–0.58)
Normal weight, BMI 18.5–24.9	11.5–16 (25–35 lb)	0.42 (0.35–0.50)
Overweight, BMI 25.0–29.9	7–11.5 (15–25 lb)	0.28 (0.23–0.33)
Obesity, BMI at least 30	5–9 (11–20 lb)	0.22 (0.17–0.27)

Source: National Academies, Table 7-3, page 254, including its first-trimester footnote. These are the table's original BMI categories and rounded units. They do not establish individual targets for every level of obesity or multiple pregnancy.

The guidance uses the same rate range for the second and third trimesters. It does not supply a universal total for each separate trimester. Do not add invented trimester subtotals to make a schedule look more precise than its source.

First Trimester Weight Gain

The table's first-trimester assumption should be kept separate from the question of why someone's weight changed. Record the change and discuss it with your maternity team rather than concluding that a small fetus makes weight loss irrelevant.

NHS morning-sickness guidance distinguishes common nausea and vomiting from severe sickness that may involve dehydration or inadequate nutrition. It advises contacting a midwife, GP or NHS 111 if you are vomiting and have lost weight. Other reasons to call include inability to keep food or fluids down for 24 hours, dark urine or no urination for more than eight hours, weakness or dizziness, abdominal pain, fever or vomiting blood. Outside the U.K., contact the corresponding local service.

Do not wait until weight loss crosses an invented percentage before seeking advice. This page does not recommend compensatory overeating, deliberate weight loss or an automatic “catch-up” plan.

Second Trimester Weight Gain

Use the table as a reference when discussing your records. To prepare for an appointment, note your prepregnancy weight, dates of measurements, units, current gestational age and any symptoms or difficulty eating. These are recordkeeping suggestions, not a clinical scoring system.

Illustrative arithmetic: A recorded change from 65.0 kg to 66.2 kg across three weeks is 1.2 kg total, or 0.4 kg/week on average. That calculation describes the recorded interval. It does not measure fetal growth, determine the cause of the change or certify an appropriate intake. The guideline's categories depend on prepregnancy BMI; a current pregnancy weight should not silently replace that starting information.

You can use the pregnancy weight-gain calculator to explore its stated assumptions. Bring an unexpected result to your care team instead of treating the display as an instruction to restrict food or force additional meals.

Third Trimester Weight Gain

The source table continues its second-trimester rate range into the third. This guide does not add an unsupported rule that weight gain must slow in the final two weeks or that a particular scale increase is “usually just fluid.”

Keep the weight record and symptoms together. NHS pre-eclampsia guidance calls for immediate assessment of symptoms including severe persistent headache, vision changes, pain below the ribs and sudden swelling of the face, hands or feet. Contact your maternity unit promptly if these occur; use the appropriate urgent local service if you cannot reach it. A weight chart cannot diagnose or exclude pre-eclampsia.

For tracking, follow the schedule agreed with your care team. Write down the scale and measurement conditions so comparisons are understandable. This article does not claim a universal daily fluctuation allowance or require an unsupported four-week waiting period before reporting a concern.

Frequently Asked Questions

How much weight should I gain by 20 weeks?

There is no single number for everyone. The guideline table gives prepregnancy-BMI-specific total and later-trimester rate ranges. A number calculated for an assumed start week is a model result, not a required milestone. Discuss your actual record and circumstances with your care team.

Is it normal to not gain weight in the first trimester?

A chart alone cannot answer that for an individual. The first-trimester assumption is not a guarantee about weight loss. If vomiting accompanies weight loss, NHS guidance advises seeking help; do not dismiss it or wait for an arbitrary percentage threshold.

Why did my weight jump suddenly in the third trimester?

Your scale reading cannot establish the cause. Record the change and contact your maternity team about a concern. If it accompanies sudden swelling, severe headache, vision problems or pain below the ribs, follow the NHS advice to seek immediate assessment, rather than assuming it is harmless fluid retention.