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The association between pre-pregnancy use of obesity medications and gestational weight gain: a retrospective cohort study

This retrospective cohort study reveals that pre-pregnancy use of obesity medications, particularly within six months of conception, is associated with a significantly increased risk of excessive gestational weight gain and adverse maternal and neonatal outcomes, underscoring the need for targeted preconception counseling and prenatal weight management strategies.

Original authors: Helena Piccinini-Vallis, Janet Green, Kristyn Reeves, Megan Campbell

Published 2026-07-01

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Helena Piccinini-Vallis, Janet Green, Kristyn Reeves, Megan Campbell

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine your body as a car preparing for a long, important journey: pregnancy. Before the trip starts, many drivers with heavy loads (higher body weight) try to lighten the car by taking special fuel additives (obesity medications) to lose weight. The goal is to start the journey with a lighter, more efficient vehicle.

However, a new study from Nova Scotia suggests that taking these additives before the trip might have a surprising side effect: once you stop taking them to start the journey, the car might actually gain more weight during the trip than expected, and the ride might become bumpier.

Here is a simple breakdown of what the researchers found:

The Big Question

Doctors usually tell people with higher body weight to lose weight before getting pregnant. The logic is simple: "Start lighter, stay on track." But there was a nagging suspicion that losing weight too quickly or using strong medications to do it might backfire. This study looked at women who used medications like Ozempic, Wegovy, Saxenda, or Contrave before getting pregnant to see what happened.

The Study Setup

The researchers acted like detectives looking at old records. They compared two groups of women who had babies between 2018 and 2024:

The "Medication Group": 222 women who had taken obesity medications before getting pregnant.
The "Control Group": 222 women who were similar in age, had similar numbers of previous babies, and started with similar weights, but didn't take those specific medications.

They matched them up like twins in a race to see who gained what kind of weight during pregnancy.

The Main Findings: The "Rebound" Effect

The study found that women who had taken these medications before pregnancy gained more weight during their pregnancy than the women who didn't.

The Numbers: The medication group gained an average of 12.4 kg (about 27 lbs), while the other group gained 9.5 kg (about 21 lbs).
The "Too Much" Problem: A much larger chunk of the medication group (61%) gained too much weight compared to the other group (43%).
The Timing Matters: The researchers found a "freshness" factor. If a woman stopped taking the medication within 6 months of getting pregnant, she was much more likely to gain excess weight. It's as if the car's engine was still revving from the fuel additive, and when the additive was cut, the car surged forward with extra momentum.

The Side Effects on the Journey

Because the weight gain was higher, the "ride" had more bumps. The study found that the medication group had higher chances of:

Gestational Diabetes: High blood sugar during pregnancy.
Preeclampsia: A dangerous condition involving high blood pressure.
C-Sections: Needing surgery to deliver the baby.
Larger Babies: The babies were more likely to be "large for their age."

Interestingly, the medication group had fewer babies that were "small for their age," suggesting the extra weight gain helped the babies grow bigger, but perhaps too big.

Why Does This Happen? (The Analogy)

The researchers offer a few guesses, but they didn't prove exactly why.

The Rebound: Think of a rubber band. When you stretch it (lose weight quickly with meds) and then let go (stop the meds), it snaps back. In pregnancy, the body is already in "growth mode," so that snap-back might combine with normal pregnancy weight gain to create a "double whammy."
The Appetite Switch: Maybe the medications changed how the body regulates hunger. When the meds stop, the body might feel extra hungry or less satisfied, leading to eating more during pregnancy.

What This Means (According to the Paper)

The paper concludes that while losing weight before pregnancy is generally good, using these specific strong medications right before getting pregnant might make it harder to control weight gain during the pregnancy.

The authors suggest that if a woman plans to get pregnant, she shouldn't just stop the meds and hope for the best. Instead, she might need a "safety net" plan—like extra support with eating habits and weight monitoring—to stop that "rebound" weight from getting out of control.

Important Note: This study looked at past records. It shows a link, but it doesn't prove that the medication caused the extra weight. It just says the two things happened together often. Also, the study was done in Nova Scotia, so these results might look slightly different in other places.

Technical Summary: Pre-pregnancy Use of Obesity Medications and Gestational Weight Gain

Problem Statement
Excess gestational weight gain (GWG) is a well-established independent risk factor for adverse maternal and neonatal outcomes, including preeclampsia, gestational diabetes (GDM), cesarean section, and offspring macrosomia. Current clinical guidelines recommend that individuals with elevated pre-pregnancy body mass index (BMI) lose weight prior to conception to enter pregnancy at a lower BMI, theoretically reducing the risk of excess GWG. However, emerging evidence suggests a paradoxical association where pre-pregnancy weight loss may actually increase the risk of excess GWG.

With the rising demand for pharmacologic weight loss interventions (specifically GLP-1 receptor agonists and combination therapies) among women of reproductive age, a critical knowledge gap exists regarding the impact of pre-pregnancy exposure to these medications on pregnancy trajectories. While these agents are contraindicated during pregnancy, pregnancies often occur during treatment or shortly after discontinuation. The specific relationship between pre-pregnancy obesity medication use, the timing of discontinuation, and subsequent GWG and pregnancy outcomes remains poorly understood.

Methodology
This study employed a population-based, retrospective cohort design utilizing linked administrative and perinatal data from Nova Scotia, Canada, covering the period from October 1, 2018, to May 31, 2024.

Data Sources: Data were linked between Health Data Nova Scotia (HDNS) for pharmacy dispensing records and the Nova Scotia Atlee Perinatal Database (NSAPDB) for pregnancy outcomes.
Study Population: The cohort included women aged 18–45 years with liveborn singleton pregnancies and no pre-existing diabetes.
Exposure Definition: "Exposed" pregnancies were defined by a pre-pregnancy prescription for obesity medications: liraglutide (Saxenda/Victoza), semaglutide (Ozempic/Wegovy), tirzepatide (Mounjaro), or naltrexone/bupropion (Contrave).
Study Design: A 1:1 matched cohort design was used. Exposed pregnancies ( $n=222$ ) were matched to unexposed controls based on maternal age (≤30 vs. >30), parity (nulliparous vs. multiparous), and pre-pregnancy BMI (<30 vs. ≥30 kg/m²).
Outcomes:
- Primary: Total GWG (kg) and concordance with Institute of Medicine (IOM) guidelines (insufficient, within, or excess).
- Secondary: Gestational diabetes (GDM), preeclampsia, mode of delivery (cesarean section), birthweight, large-for-gestational-age (LGA), small-for-gestational-age (SGA), and macrosomia.
Statistical Analysis: Missing data were handled via multiple imputation. Matched analyses utilized conditional logistic regression (implemented as stratified Cox regressions) to calculate odds ratios (OR) with 95% confidence intervals (CI). Secondary analyses within the exposed group examined the timing of the most recent prescription (≤6 months vs. >6 months prior to conception).

Key Results
The study included 444 pregnancies (222 exposed, 222 matched controls). The mean maternal age was 32.8 years, and the mean pre-pregnancy BMI was 36.9 kg/m².

Gestational Weight Gain: Exposed pregnancies demonstrated significantly higher mean GWG compared to controls (12.4 kg vs. 9.5 kg; $p=0.003$ ).
GWG Concordance: A significantly higher proportion of exposed pregnancies experienced excess GWG (60.8% vs. 43.5%; $p=0.002$ ).
Matched Analysis (Odds Ratios): After adjusting for the matched design:
- Excess GWG: Exposure was associated with increased odds (OR 1.38; 95% CI 1.30–1.47).
- Insufficient GWG: Exposure was associated with decreased odds (OR 0.86; 95% CI 0.79–0.93).
- Adverse Maternal Outcomes: Exposure was associated with higher odds of GDM (OR 1.10), preeclampsia (OR 1.50), and cesarean section (OR 1.32).
- Neonatal Outcomes: Exposure was associated with higher odds of LGA (OR 1.50) and lower odds of SGA (OR 0.56). No significant difference was found for macrosomia or birthweight means.
Timing of Exposure: Among exposed pregnancies, a prescription filled within 6 months of conception was strongly associated with excess GWG compared to prescriptions filled >6 months prior (Adjusted OR 3.29; 95% CI 1.76–6.15).

Significance and Claims
The authors claim that pre-pregnancy use of obesity medications, particularly when discontinued recently (within 6 months of conception), is associated with an increased risk of excess gestational weight gain and a constellation of adverse maternal and neonatal outcomes.

The study posits that these findings challenge the assumption that pre-pregnancy weight loss via pharmacotherapy uniformly improves pregnancy outcomes. Instead, the results suggest that the physiological and behavioral aftermath of discontinuing these medications—potentially involving rapid weight regain, altered appetite regulation, or metabolic adaptation—may predispose individuals to excessive weight accumulation during pregnancy.

Clinical Implications
The paper concludes that these findings underscore the necessity for targeted preconception counseling. Specifically, clinicians should address the potential for post-discontinuation weight regain and implement proactive weight management strategies (e.g., behavioral interventions, nutritional counseling, and early pregnancy monitoring) for women who have recently ceased obesity pharmacotherapy. The authors advocate for a more cautious and structured approach to discontinuation and follow-up in this population until further research clarifies causal mechanisms.

Limitations Noted by Authors
The authors acknowledge that the retrospective observational design precludes causal inference and that residual confounding (e.g., unmeasured weight cycling history or psychosocial factors) may exist. Additionally, pharmacy dispensing records do not confirm medication adherence or exact duration of use, limiting the precision of the timing analysis. The study population may also represent a higher socioeconomic status group due to the cost of these medications, potentially limiting generalizability.